Steven W. Lenhart, CIH
Millie P. Schafer, PhD
Mitchell Singal, MD, MPH
Rana A. Hajjeh, MD
DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention
National Institute for Occupational Safety and Health
National Center for Infectious Diseases
December 2004
This document is in the public domain and may be freely copied or reprinted.
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To receive documents or more information about occupational safety and health topics, contact the
National Institute for Occupational Safety and Health (NIOSH) at
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4676 Columbia Parkway
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or visit the NIOSH Web site at www.cdc.gov/niosh
DHHS (NIOSH) Publication No. 2005–109 (supersedes 97–146)
This booklet is a revised edition of the NIOSH document Histoplasmosis: Protecting Workers at Risk, which
was originally published in September 1997. The updated information in this booklet will help readers understand
what histoplasmosis is and recognize activities that may expose workers to the disease-causing fungus
Histoplasma capsulatum. The booklet also informs readers about methods they can use to protect themselves
and others from exposure.
Outbreaks of histoplasmosis have shared similar circumstances: People who did not know the health risks of
breathing in the spores of H. capsulatum became ill and sometimes caused others nearby to become ill when
they disturbed contaminated soil or accumulations of bird or bat manure. Because they were unaware of the
hazard, they did not take protective measures that could have prevented illness.
This booklet will help prevent such exposures by serving as a guide for safety and health professionals,
environmental consultants, supervisors, and others responsible for the safety and health of those working near
material contaminated with H. capsulatum. Activities that pose a health risk to workers at these sites include
disturbance of soil at an active or inactive bird roost or poultry house, excavation in regions where this
fungus is endemic, and removal of bat or bird manure from buildings.
Local, State, and national public health professionals may also find this booklet useful for understanding the
health risks of exposure to H. capsulatum so that they can provide guidance about work practices and
personal protective equipment. The appendix consists of a fact sheet about histoplasmosis printed in English
and Spanish. This fact sheet is intended to help educate workers and the general public about this disease. We
urge employers, health agencies, unions, and cooperatives to distribute the fact sheet to all potentially
exposed workers.
John Howard, M.D.
Director, National Institute for
Occupational Safety and Health
Centers for Disease Control and Prevention
This booklet was written by Mr. Steven W. Lenhart, Dr. Millie P. Schafer, and Dr. Mitchell Singal,
National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and
Prevention (CDC), and Dr. Rana A. Hajjeh, National Center for Infectious Diseases (NCID), also
of CDC. Secretarial support was provided by Ms. Ellen Blythe. Ms. Priscilla Wopat, Spokane
Research Laboratory, NIOSH, was the document's editor. Ms. Pauline Elliott of NIOSH, formatted the document. The cover design and respirator drawings were created by Mr. Richard A. Carlson. The histoplasmosis fact sheet was translated to Spanish by Dr. Veronica Herrera-Moreno and Dr. Tania Carreon-Valencia. The authors also extend gratitude to Dr. Donald L. Campbell, Ms. Teresa A. Seitz, Mr. Kenneth F. Martinez, and Ms. Dawn G. Tharr of NIOSH; Dr. Ted Pass II of Morehead State University; and Dr. Myat Htoo Razak for their encouragement and invaluable contributions to this work.
Page
Disclaimer
Foreword
Authors and Acknowledgments
What is histoplasmosis?
How is histoplasmosis diagnosed?
Culturing of H. capsulatum
Serologic tests
Detection of H. capsulatum antigen
Histoplasmin skin test
Where are H. capsulatum spores found?
Who can get histoplasmosis and what jobs and activities put people at risk
for exposure to H. capsulatum spores?
Should workers who might be exposed to H. capsulatum have
pre-exposure skin or blood tests?
What can be done to reduce exposures to H. capsulatum?
Excluding a colony of bats or a flock of birds from a building
Posting health risk warnings
Communicating health risks to workers
Controlling aerosolized dust when removing bat or bird manure from a building
Disinfecting contaminated material
Disposing of waste
Controlling aerosolized dust during construction, excavation, and demolition
Wearing personal protective equipment
What are the advantages and disadvantages of various kinds of respirators
for protecting workers against exposure to H. capsulatum?
Assigned protection factors
Respirator selection
Disposable and elastomeric, half-facepiece, air-purifying respirators
Powered air-purifying respirators with hood, helmet, or loose-fitting
facepiece and continuous-flow, supplied-air respirators with hood or helmet
Air-purifying, full-facepiece respirators; powered air-purifying
respirators with half-facepiece or full facepiece; and continuous-flow,
supplied-air respirators with half-facepiece or full facepiece
Pressure-demand, supplied-air respirators with full facepiece
Pressure-demand, self-contained breathing apparatuses (SCBA)
and combination pressure-demand, supplied-air respirators
with auxiliary SCBA
Summary
What personal protective equipment other than respirators should workers wear?
What other infectious agents are health risks for workers who disturb
accumulations of bat droppings or bird manure?
Cryptococcus neoformans
Chlamydia psittaci
Rabies
Where can I get more information about infectious diseases and answers
to questions about worker health and safety?
References
Appendix
Histoplasmosis Fact Sheet (in English)
Histoplasmosis Fact Sheet (in Spanish)
Protecting Workers at Risk
What is histoplasmosis?
Histoplasmosis is an infectious disease caused by
inhaling the spores of a fungus called Histoplasma
capsulatum. Histoplasmosis is not contagious; it
cannot be transmitted from an infected person or
animal to someone else.(1)
H. capsulatum is a dimorphic fungus, which means
it has two forms.(2,3) It is a mold (mycelial phase) in
soil at ambient temperatures, and after being
inhaled by humans or animals, it produces a yeast
phase when spores undergo genetic, biochemical,
and physical alterations.(3) Spores of H. capsulatum
are oval and have two sizes. Macroconidia (large
spores) have diameters ranging from 8 to 15
micrometers (µm), and microconidia (small spores) range from 2 to 5 µm in diameter.(3) Yeast cells of H. capsulatum have oval to round shapes and diameters ranging from 1 to 5 µm.(3-5)
Histoplasmosis primarily affects a person's lungs, and its symptoms vary greatly. The vast majority of infected people are asymptomatic (have no apparent ill effects), or they experience symptoms so mild they do not seek medical attention and may not even realize that their illness was histoplasmosis.(6) If symptoms do occur, they will usually start within 3 to 17 days after exposure, with an average of 10 days.(1) Histoplasmosis can appear as a mild, flu-like respiratory illness and has a combination of symptoms, including malaise (a general ill feeling), fever, chest pain, dry or nonproductive cough, headache, loss of appetite, shortness of breath, joint and muscle pains, chills, and hoarseness.(1,3,6-8)
A chest X-ray of a person with acute pulmonary
histoplamosis will commonly show a patchy pneumonitis,
which eventually calcifies.(3)
Several years ago, pulmonary calcifications were
thought to be associated with healed tuberculosis,
when a person had actually had histoplasmosis
instead. During the same period, individuals with
histoplasmosis were admitted mistakenly to tuberculosis
sanatoriums.(9) Unfortunately, some histoplasmosis
patients acquired tuberculosis while
residing in open wards with tuberculosis patients.(3)
Chronic lung disease due to histoplasmosis resembles
tuberculosis and can worsen over months or
years. Special antifungal medications are needed to
arrest the disease.(1,5,6,10-12) The most severe and rarest form of this disease is disseminated histoplasmosis, which involves spreading of the fungus to other organs outside the lungs. Disseminated histoplasmosis is fatal if untreated,(1,13) but death can also occur in some patients even when medical treatment is received.(12) People with weakened immune systems are at the greatest risk for developing severe and disseminated histoplasmosis. Included in this high-risk group are persons with acquired immunodeficiency syndrome (AIDS) or cancer and persons receiving cancer chemotherapy; high-dose, long-term steroid therapy; or other immuno-suppressive drugs.(6,12,14-18)
A person who has had histoplasmosis can experience reinfection after reexposure to H. capsulatum. Persons with immunity to H. capsulatum who become reinfected will usually experience a heightened inflammatory response, but they will
have a less severe illness of shorter duration than
what resulted from the primary infection.(3,5)
Not to be confused with reinfection, reactivation of
latent (inactive) histoplasmosis can occur in elderly
and immunocompromised individuals years after
infection by H. capsulatum.(2,5) The metabolic
activity of dormant yeasts and the methods that
enable a microorganism to escape elimination by a
host's immune system are unknown.(19)
Impaired vision can develop in some people because of a rare condition called "presumed ocular histoplasmosis syndrome."(3,5,20-22) The factors causing this condition are poorly understood, and there is no scientific basis establishing H. capsulatum as its cause.(5) Results of laboratory tests suggest that presumed ocular histoplasmosis is associated with hypersensitivity to H. capsulatum and not from direct exposure of the eyes to the microorganism. What delayed events convert the condition from asymptomatic to symptomatic are also unknown.(23) This syndrome should not be confused with the involvement of the eye associated on rare occasions with disseminated histoplasmosis.(3,5) Because the lesions of presumed ocular histoplasmosis syndrome do not progress, treatment is not necessary; however, treatment is essential with active cases of histoplasmosis of the eye.(24)
Histoplasmosis can be diagnosed by identifying
H. capsulatum in clinical samples of a symptomatic
person's tissues or secretions, testing the patient's blood serum for antibodies to the microorganism, and testing urine, serum, or other body fluids for H. capsulatum antigen.(3) On occasion, diagnosis may require a transbronchial biopsy.(14)
Culturing of H. capsulatum
Culturing clinical specimens is a standard method of microbial identification, but the culturing process for isolating H. capsulatum is costly and
time-consuming.(25) To complicate matters, positive
results are seldom obtained during the acute stage
of the illness, except from clinical specimens from
patients with disseminated histoplasmosis.(6,12,14,25-27) However, research advances in polymerase chain reaction technology have resulted in methods that provide rapid, first-line detection and prospective identification of H capsulatum in clinical samples.(24-30)
Serologic tests
Serologic evidence is often the prime factor in the
diagnosis of histoplasmosis.(31) Rapid and accurate
determination of serologic test results depends on
the proper collection, storage, and shipment of
serum specimens. Thus, following guidelines established
for these activities is essential.(31-33)
Because of their convenience, availability, and utility, the most widely accepted serologic tests are the immunodiffusion test and the complement-fixation test.(8,25-27) Serologic test results are useful when positive. However, sometimes test results are negative even when a person is sick with histoplasmosis, a situation that arises especially in patients with weakened immune systems.(6,14,26)
The immunodiffusion test qualitatively measures precipitating antibodies (H and M precipitin lines or bands) to concentrated histoplasmin.(8,14,34) While this test is more specific for histoplasmosis (i.e., a person who is not infected with H. capsulatum is unlikely to have a positive test result) than the complement- fixation test, it is less sensitive (i.e., someone who is acutely infected can have a negative test result).(8,14,25) Because the H band of the immunodiffusion test is usually present for only 4 to 6 weeks after exposure, it indicates active infection.(6,8,25) The M band is observed more frequently, appears soon after infection, and may persist up to 3 years after a patient recovers.(8,14)
The complement-fixation test, which measures antibodies to the intact yeast form and mycelial (histoplasmin) antigen, is more sensitive but less specific than the immunodiffusion test.(14) Complement-fixing
antibodies may appear in 3 to 6 weeks (sometimes
as early as 2 weeks(34)) following infection by
H. capsulatum, and repeated tests will give positive
results for months.(6,34) The results of complementfixation
tests are of greatest diagnostic usefulness
when both acute and convalescent serum specimens
can be obtained. A high titer (1:32 or higher) or a
fourfold increase is indicative of active histoplasmosis.(
8,26,27,34) Lower titers (1:8 or 1:16), although less
specific, may also provide presumptive evidence of
infection,(7,25) but they can also be measured in the
serum of healthy persons from regions where histoplasmosis
is endemic.(27) Antibody titers will gradually
decline and eventually disappear months to
years after a patient recovers.(6,8,25,34)
Detection of H. capsulatum antigen
A radioimmunoassay method can be used to measure
H. capsulatum polysaccharide antigen (HPA)
levels in samples of a patient's urine, serum, and other body fluids.(12,25,35,36) The test appears to meet the important need for a rapid and accurate method for early diagnosis of disseminated histoplasmosis, especially in patients with AIDS.(12,25,36) HPA is detected in body fluid samples of most patients with disseminated infection and in the urine and serum of 25% to 50% of those with less severe infections.(25)
Histoplasmin skin test
The manufacturing of diluted histoplasmin for skin
testing was stopped in January, 2000. The skin testing
reagents were still unavailable when these
guidelines were updated in 2004. A person could
learn from a histoplasmin skin test whether he or
she had been previously infected by H. capsulatum.
This test, similar to a tuberculin skin test, had been
available at many physicians' offices and medical clinics. A histoplasmin skin test became positive 2 to 4 weeks after a person was infected by H. capsulatum, and repeated tests usually gave positive results for the rest of the person's life.(26) While histoplasmin skin test information was useful to epidemiologists, a positive skin test did not help diagnose acute histoplasmosis, unless a previous
skin test was known to have been negative.(6,8,14) A
previous infection by H. capsulatum can provide
partial protection against ill effects if a person is
reinfected.(34) Since a positive skin test does not
mean that a person is completely protected against
ill effects,(34) appropriate exposure precautions
should be taken regardless of a worker's skin-test status in the past.
H. capsulatum grows in soils throughout the
world.(2,14) In the United States, the fungus is
endemic and the proportion of people infected by
H. capsulatum is higher in central and eastern
states, especially along the Ohio and Mississippi
River valleys.(3,8,37) The fungus seems to grow best
in soils having a high nitrogen content, especially
those enriched with bird manure or bat droppings.
The organism can be carried on the wings, feet, and
beaks of birds and infect soil under roosting sites or
manure accumulations inside or outside buildings.
Active and inactive roosts of blackbirds (e.g., starlings,
grackles, red-winged blackbirds, and cowbirds)
have been found heavily contaminated by
H. capsulatum.(34,38,50) Therefore, the soil in a stand
of trees where blackbirds have roosted
for 3 or more years should be suspected of being
contaminated by the fungus.(42,51) Habitats of
pigeons(38-40,52-54) and bats,(38,55-72) and poultry houses with dirt floors(38,73-78) have also been found contaminated by H. capsulatum.
On the other hand, fresh bird droppings on surfaces such as sidewalks and windowsills have not been shown to present a health risk for histoplasmosis because birds themselves do not appear to be infected by H. capsulatum.(34,79) Rather, bird manure is primarily a nutrient source for the growth of H. capsulatum already present in soil.(27) Unlike birds, bats can become infected with H. capsulatum and consequently can excrete the organism in their droppings.( 27,62,65,80)
Increasing numbers of resident Canada geese in
urban and suburban areas have caused concern
about whether droppings and water contaminated
by their droppings are possible sources of disease
transmission to humans. As with exposures to the
fresh droppings of other birds, exposures to goose
droppings have not been shown to be a health risk
for histoplasmosis. However, the human pathogens
Cryptosporidium, Giardia, and Campylobacter
have been found in Canada goose droppings.(81-83) The fecal-oral route is the primary route of ingesting pathogens that could cause infection and disease, notably diarrhea and gastroenteritis.(82) Thus, people working in areas frequented by Canada geese, such as ground maintenance workers at golf courses and parks, should take precautions to prevent hand-to-mouth contact with droppings.(81)
To learn whether soil or droppings are contaminated
with H. capsulatum spores, samples must be collected
and cultured. The culturing process involves inoculating
mice with small portions of a sample, sacrificing
the mice after 4 weeks, and streaking agar plates
with portions of each mouse's liver and spleen.(38) Then for four more weeks, the plates are watched for the growth of H. capsulatum. Enough samples must be collected so that small but highly contaminated areas are not overlooked. On several occasions, H. capsulatum has not been recovered from any of the samples collected from material believed responsible for causing illness in people diagnosed from the results of clinical tests as having histoplasmosis.( 39,40,61,74,84-86) Molecular techniques, such as polymerase chain reaction methods that produce results in days instead of weeks, may provide less costly and quicker methods of analyzing soil samples for H. capsulatum.(87)
Until a less expensive and more rapid method is
available, testing field samples for H. capsulatum
will be impractical in most situations. Consequently,
when thorough testing is not done, the safest
approach is to assume that the soil in regions where
H. capsulatum is endemic and any accumulations of
bat droppings or bird manure are contaminated with H. capsulatum and to take appropriate exposure
precautions.
Anyone working at a job or present near activities
where material contaminated with H. capsulatum
becomes airborne can develop histoplasmosis if
enough spores are inhaled. After an exposure, how
ill a person becomes varies greatly and most likely
depends on the number of spores inhaled and a person's age and susceptibility to the disease. The number of inhaled spores needed to cause disease is unknown. Generally, very few people will develop symptomatic disease after a low-level exposure to material contaminated with H. capsulatum spores. However, longer durations of exposure and exposure to higher concentrations of airborne contaminated material increase a person's risk of developing histoplasmosis.(5) Children younger than 2 years of age, persons with compromised immune systems, and older persons, in particular those with underlying illnesses such as diabetes and chronic lung disease, are at increased risk for developing symptomatic histoplasmosis.(3,4,14,88)
The U.S. Public Health Service (USPHS) and the
Infectious Diseases Society of America (IDSA)
have jointly published guidelines for the prevention
of opportunistic infections in persons infected with
the human immunodeficiency virus (HIV).(89) The
USPHS/IDSA Prevention of Opportunistic
Infections Working Group recommended that HIVinfected
persons "should avoid activities known to be associated with increased risk (e.g., creating dust when working with surface soil; cleaning chicken coops that are heavily contaminated with droppings; disturbing soil beneath bird-roosting sites; cleaning, remodeling, or demolishing old buildings; and exploring caves)."(89) HIV-infected persons should consult their health care provider about appropriate exposure precautions that should be taken for any activity with a risk of exposure to
H. capsulatum.
Below is a partial list of occupations and hobbies
with risks for exposure to H. capsulatum spores.
Appropriate exposure precautions should be taken
by these people and others whenever contaminated
soil, bat droppings, or bird manure is disturbed.
- Bridge inspector or painter(55,63,72,86)
- Chimney cleaner(66)
- Construction worker(12,57,58,67,85,90)
- Demolition worker(7,57,73)
- Farmer(7,12,74–77,86)
- Gardener(7,78,91)
- Heating and air-conditioning system installer or
service person(8,61)
- Microbiology laboratory worker(23,53,64,86)
- Pest control worker
- Restorer of historic or abandoned buildings(61,64)
- Roofer(52)
- Spelunker (cave explorer)(56,59,60,68–71)
If someone who engages in these activities develops flu-like symptoms days or even weeks after disturbing material that might be contaminated with H. capsulatum, and the illness worsens rather than subsides after a few days, medical care should be sought and the health care provider informed about the exposure.
Outbreaks of histoplasmosis have occurred
among people who were infected by H. capsulatum
even though they had no part in the activities
that caused contaminated material to become
aerosolized.(39,52,92,93)
After a small group of students raked and swept a
20-year accumulation of dirt, leaves, and debris in a
middle school's courtyard on Earth Day-1970, nearly 400 people (mostly students) developed
histoplasmosis.(92) The school's forced-air ventilation system, which had fresh air intakes in the courtyard, was implicated as being primarily responsible for spreading contaminated air throughout the school. Results of the outbreak investigation showed that a few students developed histoplasmosis despite being absent from school on the day when the courtyard was cleaned. This finding suggests that exposures to spore-contaminated dust continued for a day or more after cleaning of the courtyard was stopped.
During a histoplasmosis outbreak in 2001, 523 people
(439 of them were students) met a laboratoryconfirmed
case definition of histoplasmosis following
the rototilling of a 10-foot by 45-foot area of soil
within a high school's courtyard.(93) Spore-contaminated air entered a wing of the school most likely through open windows that faced the courtyard and heating, ventilating, and air-conditioning systems that had fresh air intakes in the courtyard. As with the 1970 Earth Day outbreak, this study's findings also showed that a few persons were infected despite being absent from school on the day of the rototilling activity and the following day.
If a histoplasmin test was available again, workers
at risk of exposure to H. capsulatum might learn
useful information from skin testing. The results of
skin testing would inform each worker of his or her
status regarding either susceptibility to infection by
H. capsulatum (a negative skin test) or partial protection
against ill effects if reinfected (a positive
skin test). However, a false-negative skin test result
can be reported early in an infection or with persons
with weakened immune systems.(6,8,14,26,34) A
false-positive skin test can result from cross-reactions
with antigens of certain other pathogenic
fungi.(8,37) One drawback to routine pre-exposure
skin testing is that a person with a positive skin test might incorrectly assume a false sense of security
that he or she is completely protected against ill
effects if reinfected. The work practices and personal
protective equipment described in this booklet
are expected to protect both skin-test positive
and skin-test negative persons from excessive
inhalation exposures to materials that might be contaminated
with H. capsulatum.
Although a pre-exposure serum sample could be
useful in determining whether a worker's post-exposure illness is histoplasmosis, routine collection and storage of serum specimens from workers is unnecessary and impractical in most work settings. Some employers, such as public health agencies and microbiology laboratories, have facilities for long-term storage of serum and do collect pre-exposure serum specimens from those employees who might be exposed to high-risk infectious agents. If a worker is to have blood drawn for this purpose and is to receive a histoplasmin skin test, the blood sample should be drawn first because the skin test may cause a positive complement-fixation test for up to 3 months and the appearance of the M band on an immunodiffusion test for H. capsulatum.(1,7,8,26)
Excluding a colony of bats or
a flock of birds from a building
Although a primary focus of this booklet is how
to protect the health of workers cleaning up accumulated
bat or bird manure, the best work practice is to
prevent the accumulation of manure in the first place.
Therefore, when a colony of bats or a flock of birds is
discovered roosting in a building, immediate action
should be taken to exclude the intruders by sealing all
entry points. Any measure that might unnecessarily
harm or kill a bat or bird should be avoided.
Before excluding a colony of bats or a flock of birds
from a building, attention should be given to the
possibility that flightless young may be present. In the United States, this is an especially important
consideration for bats from May through August.(94)
Ultrasonic devices and chemical repellents are ineffective for eliminating bats from a roosting area.(95) The most effective way of excluding bats from an occupied roost involves following five basic steps to identify and seal entry and exit points.(94) Because some bat species are so small that they can squeeze through an opening as small as the diameter of a dime,(94) even the smallest hole should be sealed. When openings are inaccessible, installing and maintaining lights in a roosting area will force bats to seek another daytime roosting site. Because of concerns for the welfare of evicted bats, constructing bat houses near former roosts has become a common practice.(94,96)
In some buildings, extensive bat exclusion measures
may be more successful in the late fall or
winter months after a colony has migrated to a
warmer habitat or to another location for hibernation.
In some regions of the United States, bats may
not migrate, but rather will hibernate in the same
building. Consequently, any work on a building that
might disturb such a colony should be delayed until
spring. Disturbing bats during hibernation is likely
to result in their death.In some buildings, extensive bat exclusion measures
may be more successful in the late fall or
winter months after a colony has migrated to a
warmer habitat or to another location for hibernation.
In some regions of the United States, bats may
not migrate, but rather will hibernate in the same
building. Consequently, any work on a building that
might disturb such a colony should be delayed until
spring. Disturbing bats during hibernation is likely
to result in their death.
Excluding birds from a building also involves blocking access to indoor roosts and nesting areas.(97) Because their food source is usually nearby, birds prevented from reentering a building will often complicate an exclusion by beginning to roost on window sills and ledges of the building or others nearby. Visual deterrents (e.g., balloons, flags, lights, and replicas of hawks and owls) and noises (e.g., gun shots, alarms, gas cannons, and fireworks) may scare birds away, but generally only temporarily.(97)
Nontoxic, chemical bird repellents are available as liquids, aerosols, and nondrying films and pastes. Disadvantages of these antiroosting materials are that some are messy and none are permanent. Even the most effective ones require periodic reapplication.
More permanent repellents include mechanical
antiroosting systems consisting of angled and porcupine
wires made of stainless steel. These systems
may require some occasional maintenance to clear
nesting material or other debris from the wires.(97)
Pigeons can be controlled by capturing them in
traps placed near their roosting, loafing, or feeding
sites.(97) Shooting birds, using contact poisons, and
baiting with poisoned food should be used as last
resorts and should only be done by qualified pest
control specialists. Using such methods to kill nuisance
birds may also require a special permit.
Posting health risk warnings
If a colony of bats or a flock of birds is allowed to
live in a building or a stand of trees, their manure
will accumulate and create a health risk for anyone
who enters the roosting area and disturbs the material.
Once a roosting site has been discovered in a
building, exclusion plans should be made, and the
extent of contamination should be determined.
When an accumulation of bat or bird manure is discovered
in a building, removing the material is not
always the next step. Simply leaving the material
alone if it is in a location where no human activity
is likely may be the best course of "action."
Areas known or suspected of being contaminated
by H. capsulatum, such as bird roosts, attics, or
even entire buildings that contain accumulations of
bat or bird manure, should be posted with signs
warning of the health risk. Each sign should provide
the name and telephone number of a person to be
contacted if there are questions about the area. In
some situations, a fence may need to be built around
a property or locks put on attic doors to prevent
unsuspecting or unprotected individuals from
entering.
Communicating health risks to workers
Before an activity is started that may disturb any material that might be contaminated by H. capsulatum, workers should be informed in writing of the personal
risk factors that increase an individual's chances of developing histoplasmosis. Such a written communication should include a warning that individuals with weakened immune systems are at the greatest risk of developing severe and disseminated histoplasmosis if they become infected. These people should seek advice from their health care provider about whether they should avoid exposure to materials that might be contaminated with H. capsulatum. The fact sheet in the appendix is one way of conveying information about histoplasmosis; it can be distributed to workers during their hazard communication training.
Controlling aerosolized dust when removing
bat or bird manure from a building
The best way to prevent exposure to H. capsulatum
spores is to avoid situations where material that
might be contaminated can become aerosolized and
subsequently inhaled. A brief inhalation exposure to
highly contaminated dust may be all that is needed
to cause infection and subsequent development of
histoplasmosis. Therefore, work practices and dust
control measures that eliminate or reduce dust generation
during the removal of bat or bird manure
from a building will also reduce risks of infection
and subsequent development of disease. For example,
instead of shoveling or sweeping dry, dusty
material,(39) carefully wetting it with a water spray
can reduce the amount of dust aerosolized during an
activity. Adding a surfactant or wetting agent to the
water might reduce further the amount of
aerosolized dust. Once the material is wetted, it can
be collected in double, heavy-duty plastic bags, a
55-gallon drum, or some other secure container for
immediate disposal. An alternative method is use of
an industrial vacuum cleaner with a high-efficiency
filter to "bag" contaminated material. Truck-mounted or trailer-mounted vacuum systems are recommended for buildings with large accumulations of bat or bird manure. These high-volume systems can remove tons of contaminated material in a short period. Using long, large-diameter hoses, such a system can also remove contaminated material located several stories
above its waste hopper. This advantage eliminates the
risk of dust exposure that can happen when bags tear
accidentally or containers break during their transfer
to the ground.
The removal of all material that might be contaminated
by H. capsulatum from a building and immediate
waste disposal will eliminate any further risk
that someone might be exposed to aerosolized
spores. Air sampling, surface sampling, or the use
of any other method intended to confirm that no
infectious agents remain following removal of bat
or bird manure is unnecessary in most cases.
However, before a removal activity is considered
finished, the cleaned area should be inspected visually
to ensure that no residual dust or debris
remains.
Disinfecting contaminated material
Disinfectants have occasionally been used to treat
contaminated soil and accumulations of bat manure
when removal was impractical or as a precaution
before a removal process was started.(41,48-50,61,67) To date, formaldehyde solutions have been the only disinfectants proven to be effective for decontaminating soil containing H. capsulatum.(41,48-50) Exposures to formaldehyde through ingestion, inhalation, and skin and eye contact can cause a variety of adverse health effects.(98) Several years ago, applicators exposed to formaldehyde during soil disinfection activities reported burning eyes and mucous membrane irritation.(48) Workers at another site experienced nausea and vomiting.(41)
Today, although a number of EPA-registered fungicidal
products contain formaldehyde, none of them
is registered for use as a soil disinfectant. Thus,
using a formaldehyde containing product to disinfect
soil would be inappropriate. Furthermore, there
is no product or chemical that is registered by the
EPA that has the specific claim of being effective
against H. capsulatum. A manufacturer of a product
claiming to disinfect soil contaminated with
H. capsulatum will have to meet the EPA's regulatory requirements and complete the registration
process.
Should an EPA-registered product become available
to disinfect land contaminated by H. capsulatum,
measures should be taken to ensure that the disinfectant
penetrates deeply enough to contact all the
soil containing H. capsulatum. While H. capsulatum
was found in a blackbird roost at a depth of more
than 12 inches,(99) soil saturation to a depth of 6 to 8
inches will be sufficient for most disinfectant applications.(
38,48) To evaluate a disinfectant's effectiveness, soil samples should be collected before and after an application and analyzed for H. capsulatum. The appropriate number of samples to be collected will vary depending upon the size of the property.(38,100) Each sampling location should be flagged or marked in a way that will ensure that the same locations will be sampled after application of the disinfectant. A map of the treated area showing the approximate location of each sampling site will also be useful in the event flags or markings are lost. After a disinfectant's effectiveness has been documented— more than one application may be necessary— additional tests for H. capsulatum should be done periodically if the land remains idle.
Disposing of waste
Any material that might be contaminated with
H. capsulatum that is removed from a work site
should be disposed of or decontaminated properly
and safely and not merely moved to another area
where it could still be a health hazard. Before an
activity is started, the quantity of material to be
removed should be estimated. (If the approximate
volume of dry bat or bird manure in a building is
known, the approximate weight can be calculated
using a conversion factor of 40 pounds per cubic
foot.) Requirements established by local and state
authorities for the removal, transportation, and disposal
of contaminated material should be followed.
Arrangements should be made with a landfill operator
concerning the quantity of material to be disposed
of, the dates when the material will be delivered,
and the disposal location. If local or state land-fill regulations define material contaminated with
H. capsulatum to be infectious waste, incineration
or another decontamination method may also be
required.
Controlling aerosolized dust during
construction, excavation, and demolition
Dusts containing H. capsulatum spores can be
aerosolized during construction, excavation, or
demolition. Once airborne, spores can be carried
easily by wind currents over long distances. Such
contaminated airborne dusts can cause infections not
only in persons at a work site, but also in others
nearby. Such activities were suggested as the causes
of the three largest outbreaks of histoplasmosis ever
recorded. All three outbreaks took place in
Indianapolis, Indiana.(25,85,88,101) During the first
outbreak, in the fall of 1978 and spring of 1979, an
estimated 120,000 people were infected, and 15 people
died. The second outbreak, in 1980, was similar
to the first in the number of people affected. AIDS
patients accounted for nearly 50% of culture-proven
cases during the third outbreak, which began in 1988
and lasted until 1993.(101)
Water sprays or other dust suppression techniques
should be used to reduce the amount of dust
aerosolized during construction, excavation, or
demolition in regions where H. capsulatum is
endemic. During windy periods or other times when
typical dust suppression techniques are ineffective,
earthmoving activities should be interrupted. All
earthmoving equipment (e.g., bulldozers, trucks,
and front-end loaders) should have cabs with airconditioning
(if available) to protect their operators.
Air filters on air-conditioners should be inspected
on a regular schedule and cleaned or replaced as
needed. During filter cleaning or replacement of
exceptionally dusty air filters, respiratory protection
should be worn by the maintenance person if there
is a potential for the dust to be aerosolized. Beds of
all trucks carrying dirt or debris from a work site
should be covered, and all trucks should pass
through a wash station before leaving the site.
When at a dump site, a truck operator should ensure
that all individuals in the vicinity are in an area where they will not be exposed to dust aerosolized
while the truck is emptied.
Water sprays and other suppression techniques may
not be enough to control dust aerosolized during
demolition of a building or other structure.
Consequently, removal of accumulations of bird or
bat manure before demolition may be necessary in
some situations. Factors affecting decisions about
pre-demolition removal of such accumulations
include the quantity and locations of the material,
the structural integrity or soundness of the building,
weather conditions, proximity of the building to
other buildings and structures, and whether nearby
buildings are occupied by persons who may be at
increased risk for developing symptomatic histoplasmosis
(e.g., schools, day-care facilities, hospitals,
clinics, jails, and prisons).
City or county governments in regions where
H. capsulatum is endemic should establish and
enforce regulations concerning work practices that
will control dust aerosolization at construction,
excavation, and demolition sites. However, even in
regions where H. capsulatum is not considered
endemic, dust aerosolized during work activities in
bird roosts has also resulted in outbreaks of histoplasmosis.(
40,45) Consequently, regardless of
whether a work site is in an endemic region, precautions
should be taken at active and inactive bird
roosts to prevent dust aerosolization.
Wearing personal protective equipment
Because work practices and dust control measures
to reduce worker exposures to H. capsulatum have
not been fully evaluated, using personal protective
equipment is still necessary during some activities.
During removal of an accumulation of bat or bird
manure from an enclosed area such as an attic, dust
control measures should be used, but wearing a
NIOSH-approved respirator and other items of personal
protective equipment is also recommended to
reduce further the risk of H. capsulatum exposure.
For some jobs involving exposures to airborne dusts,
working conditions have changed little over the years despite improvements in other aspects of the
industry. For example, inhalation of dust aerosolized
from the dirt floors of chicken coops that contained
H. capsulatum spores was reported more than 40
years ago as the cause of clinical cases of histoplasmosis
in workers.(73-77) As the poultry industry has grown, the old-style chicken coop has been replaced by larger housing facilities. In the United States in 2002, approximately 82,400 farms produced eggs or poultry including layers, pullets, broilers, turkeys, ducks, and geese.(102) However, the floors of most poultry houses are still dirt covered and provide an excellent medium for the growth of H. capsulatum. Ventilation systems in poultry houses are not primarily intended to reduce poultry workers' exposures to aerosolized dust, and dust measurements made during growing and catching chickens show that inhalation exposures of poultry workers to dust can be excessive.(103) Since ventilation systems designed especially to reduce airborne dust to "safe" levels in poultry houses would likely be economically and mechanically impractical, wearing a respirator is probably the most feasible method for protecting poultry workers.
Recommendations for selecting respirators to protect
workers against inhalation exposures to airborne dust
and H. capsulatum are described next. Following
that, recommendations for personal protective equipment
other than respirators are provided.
Assigned protection factors
Respirators provide varying levels of protection,
and people have developed histoplasmosis after disturbing
material contaminated with H. capsulatum
despite wearing either a respirator or a mask that
they assumed would protect them.(60,71,104) Such
unfortunate events demonstrate that when a respirator
is needed, it must be carefully selected with an
understanding of the circumstances associated with exposure to an airborne contaminant and the
capabilities and limitations of the various kinds of
respirators.
Because respirators provide different levels of protection,
they are divided into classes, and each respirator
class has been assigned a protection factor to
help compare its protective capabilities with other
respirator classes. An assigned protection factor is a
unitless number determined statistically from a set
of experimental or workplace data. This factor is the
minimum level of protection expected for a substantial
proportion (usually 95%) of properly fitted
and trained respirator users.(105)
When the effectiveness of a respirator is evaluated
in a workplace, a protection factor is calculated for
each respirator wearer and respirator combination
by dividing the air concentration of a challenge
agent by the air concentration of that agent inside
the respirator wearer's facepiece, hood, or helmet. For example, if air sampling measurements show equal concentrations of a contaminant inside and outside a respirator wearer's facepiece, then the respirator provided no protection, and a protection factor of 1 would be calculated. Likewise, a protection factor of 5 means that a respirator wearer was exposed to one-fifth (20%) of the air concentration to which he or she would have been exposed if a respirator had not been used, a reduction of 80%. Similarly, a protection factor of 10 represents a onetenth (10%) exposure (a 90% reduction), 50 represents a one-fiftieth (2%) exposure (a 98% reduction), and so on.
The assigned protection factors of respirators available
for protecting workers against exposures to airborne
materials contaminated with H. capsulatum
range from 10 to 10,000.(106,107,108) Disposable respirators
and elastomeric half-facepiece respirators
represent the low end of the protection-factor scale.
Self-contained breathing apparatuses operated in
the pressure-demand mode, represent the high end.
Within this range is a variety of negative-pressure,
powered air-purifying, and supplied-air respirators that are available with half-facepiece, full facepiece,
loose-fitting facepiece, hood, or helmet.
Later in this section, the advantages and disadvantages
of these various respirators are described.
Respirator selection
Before the specific types of respirators are
described, it is important to understand the information
that is usually needed to select a respirator
for a particular activity.
The hazard ratio method, or the industrial hygiene
method, is a quantitative method used most commonly
to select respirators for noninfectious
aerosols, gases, and vapors. Using this method
requires estimates of the air concentrations of a contaminant
measured during a person's work activities and knowledge of the established (or recommended) occupational exposure limits of that contaminant. A minimum level of respiratory protection is calculated by dividing the highest air concentration measurement by the most protective occupational exposure limit of the contaminant. A respirator from the respirator class having an assigned protection factor equal to or exceeding this value would then be selected. For example, assume a set of air samples collected during a particular job resulted in exposure estimates ranging from 8 to 50 milligrams per cubic meter (mg/m3) of sampled air for a contaminant having occupational exposure limits of 5 mg/m3 and 10 mg/m3. Given this information, a respirator with an assigned protection factor of at least 10 (50 mg/m3 ÷ 5 mg/m3 = 10) should be selected. However, applying the hazard ratio method to respirator selection decisions for infectious aerosols is difficult and often impossible.(109)
Unfortunately, published air sampling data on H. capsulatum spores are either outdated or too limited,( 68-70,76,80,110,111) and no numerical exposure limit exists for H. capsulatum. In situations such as this, when the important data needed for the hazard ratio method are either uncertain or unavailable, the expert opinion method is usually used.(109) This method is a qualitative approach to making decisions about respirators based on the subjective professional
judgment of one or more experts. Respirator selection
is made after considering the characteristics of
job activities that are recognized or anticipated to
involve risks of exposure to airborne contaminants;
consideration of the properties of the specific agent
involved and health effects of overexposure; and
knowledge of the assigned protection factors, advantages,
and disadvantages of various respirators.(109)
In this application of the expert opinion method, categorical
risk estimates were developed with the
levels of recommended respiratory protection
increasing as the perceived levels of exposure
increased.(109)
The following respirator selection information
describes classes of respirators in order of increasing
assigned protection factors. The assigned protection
factors used here are from Table 1 of the
NIOSH Respirator Selection Logic.(106) Respirators
that should be worn during work activities involving
exposures to spore-contaminated airborne dusts
range from disposable, filtering facepiece respirators
for low-risk situations (e.g., site surveys of bird
roosts) to full-facepiece, powered air-purifying respirators
for extremely dusty work (e.g., removing
accumulated bird or bat manure from an enclosed
area such as an attic).
Regardless of which respirator is selected, the
device should be NIOSH-certified and used in the
context of a respiratory protection program.
Important components of such a program are facepiece
fit-testing, respirator maintenance, user training,
medical evaluation of users, respiratory protection
program evaluation, and recordkeeping.(112,113)
Disposable and elastomeric,
half-facepiece, air-purifying respirators
(assigned protection factor: 10)
A half-facepiece respirator covers the wearer's nose
and mouth. Because inhalation creates a slight negative
pressure inside the facepiece of non-powered,
air-purifying respirators with respect to outside,
these respirators are also called negative-pressure respirators. During inhalation, contaminated air can easily enter the facepiece of a negative-pressure respirator at gaps between the facepiece and the respirator wearer's face. Therefore, a complete face-tofacepiece seal is essential for good protection. The findings of a study to evaluate faceseal leaks of an elastomeric half-facepiece respirator showed that 89% of the leaks occurred at the nose or chin or were multiple leaks that included these locations.( 114) Facial hair (even the stubble of a few days' growth), absence of one or both dentures, and deep facial scars can also prevent a complete seal.
Whereas elastomeric half-facepiece respirators consist
of a reusable elastomeric or rubber facepiece
and replaceable filters, most disposable respirators
are filtering facepieces in which the facepiece is the
dust filter. Disposable respirators and replaceable
filters can be used until they are difficult to breathe
through, damaged, or malodorous.
A disadvantage of any negative-pressure, air-purifying
respirator is that resistance to inhalation
increases as the filters load with dust. For disposable
respirators without exhalation valves, filter
loading increases resistance during exhalation as
well as inhalation. This effect, combined with the
warm, moist air inside the facepiece, is so uncomfortable
for some people that they do not wear a respirator
as frequently as they should, or they stop
wearing one entirely.
As of July 10, 1995, NIOSH began certification of
negative-pressure, air-purifying particulate filters
under new regulations (42 CFR Part 84).(115) All particulate-
filtering respirators certified by NIOSH
under previous regulations (30 CFR Part 11) were no
longer sold after July 10, 1998, and only Part 84 particulate
respirators are now available. Part 84 particulate
respirators have the prefix TC-84A. Part 84 particulate
filters are divided into nine classes, and filters
from any class can be selected for protection against
inhalation of H. capsulatum spores. A filter's class (e.g., N-95) and "NIOSH" are marked on the facepiece, exhalation valve cover, or head straps of disposable respirators, and on filter cartridges and cartridge boxes.
Although Part 84 improved the requirements for particulate
filters, the facepiece fitting characteristics of
all particulate respirators became exempt from evaluation
as a condition of NIOSH certification.(116)
Thus, only respirators with good fitting characteristics
should be purchased, and it is essential that
workers are assigned respirators based on the results
of facepiece fit-testing. To aid in the selection of filtering
facepiece respirators for fit testing, studies
have been published on the fitting characteristics of
some of them.(116,117)
The type of head straps on the various disposable
and elastomeric half-facepiece respirators is an
important but frequently overlooked consideration.
Head strap tension is important for achieving a
complete face-to-facepiece seal without sacrificing
comfort. Elastomeric facepieces have adjustable
straps, which should allow a respirator wearer to
make a complete, yet comfortable, facepiece seal.
On the other hand, not all disposable respirators
have adjustable straps; some simply have fixedlength
elastic bands. Most disposable respirators
certified under Part 84, do not have adjustable straps,
only elastic bands. Research has not been done to
evaluate whether the facepiece fits of respirators
with adjustable straps differ significantly from those
of respirators with elastic bands. However, a respirator
user should be aware that the fit and comfort of a
disposable respirator with elastic bands might differ
from one with adjustable straps.
In dusty conditions, repeated exposure of the eyes
to dust increases the risk for injury and disease.
Most dust particles entering a person's eyes will be
washed out by tears, but some particles can be
retained, particularly within the margin of the
upper eyelid. Depending on their size, shape, and
composition, these particles can become embedded
in the surface of the cornea or sclera, where they
cause irritation and then reddening of the surface.
If not removed, such particles may produce eye
infections.(118) Therefore, a half-facepiece respirator
is a poor choice for use in dusty conditions.
While wearing eyecup goggles may provide some
eye protection, they are not airtight and do not
completely prevent dust exposure. Furthermore,
goggles may interfere with a respirator's fit. For these reasons, a full-facepiece respirator is a better alternative when a person's eyes are at risk of exposure to airborne dusts.
Because their assigned protection factors are lower
than those of other respirator types, the use of disposable
or elastomeric half-facepiece respirators
should be limited to situations where risks are low
for inhaling material that might be contaminated
with H. capsulatum spores. Situations that could be
considered low risk include site surveys of bird
roosts, collecting soil samples, or maintenance on
filters of earthmoving equipment. However, during earthmoving activities at bird roosts or other work
sites where the soil is known to be heavily contaminated
by H. capsulatum, air-purifying, half-facepiece
respirators should be worn by equipment operators to
supplement dust suppression methods and the use of
equipment with cabs.
Powered air-purifying respirators
with loose-fitting facepiece and
continuous-flow, supplied-air
respirators with hood or helmet
(assigned protection factor: 25)
A powered air-purifying respirator uses a small
battery-operated blower to draw dusty air through
attached filters and provides clean air at a constant
flow rate of 170 liters per minute (L/min). This flow
rate is usually greater than a wearer's breathing rate. Consequently, gaps in a face-to-facepiece seal will leak air outward rather than inward. Another advantage of these respirators is that they provide built-in eye protection. They are also the only respirators that adequately protect bearded workers.
Because powered air-purifying respirators cause
almost no breathing resistance, the discomfort that
some people experience while wearing a negativepressure
respirator is reduced. Interviews with 117
agricultural workers (53 swine farmers, 46 grain
handlers, and 18 poultry farmers), found that powered
air-purifying respirators with loose-fitting
facepieces were rated best over disposable and elastomeric
half-facepiece respirators for breathing ease,
communication ease, skin comfort, and in-facepiece
temperature and humidity.(119) Disposable respirators
were rated best for weight and convenience.
Powered air-purifying respirators with particulate
filters approved by NIOSH under the regulations of
42 CFR Part 84 have the prefix TC-84A. Only powered
air-purifying respirators with high-efficiency
filters are approved by NIOSH under Part 84.
Supplied-air respirators are not air-purifying types,
but deliver breathing air from an air compressor or
compressed air cylinder through a pressurized hose to the facepiece. Continuous-flow, supplied-air
respirators with loose-fitting facepieces also provide
a minimum air flow rate of 170 L/min. The
maximum air flow rate of a continuous-flow supplied-
air respirator may not exceed 425 L/min. Air
supply hoses are available in a variety of lengths up
to a maximum of 300 feet. All NIOSH-approved,
supplied-air respirators have the prefix TC-19C.
An advantage of a supplied-air respirator is that the source of the breathing air does not depend upon filters to purify ambient air. An advantage of continuous- flow, supplied-air respirators is that when an activity involves work in a hot environment, such as an attic or a chicken house in the summer, a vortex tube can be added to the device that will cool the air flowing to the respirator wearer. A disadvantage of a supplied-air respirator is that if its air supply hose is too short, then mobility of the respirator wearer will be restricted. Also, in some situations (in attics or on elevated structures for example), the trailing hose of a supplied-air respirator can be a tripping hazard.
While the respirators described in this section have
higher assigned protection factors than disposable
or elastomeric half-facepiece respirators, they may
not provide enough protection in extremely dusty
conditions where air concentrations of H. capsulatum
spores may be high, especially in enclosed
spaces. Examples of activities for which respirators
with higher assigned protection factors may be
more important include cleaning chimneys(66) and
working in attics(58,61,67) and poultry houses.(74-77)
Air-purifying, full-facepiece respirators;
powered air-purifying respirators with
half-facepiece or full facepiece; and
continuous-flow, supplied-air respirators
with half-facepiece or full facepiece
(assigned protection factor: 50)
A full-facepiece respirator extends from the forehead
to under the chin. It also has the built-in benefit
of providing eye protection as well as respiratory protection. As with other negative-pressure respirators,
a complete face-to-facepiece seal is essential
for good protection. However, partly because a good
fit is easier with a full-facepiece, negative-pressure
respirator, this type has a higher assigned protection
factor than half-facepiece types. Fogging of a fullfacepiece
lens can obstruct vision, but this problem
is preventable by adding a nosecup inside the facepiece.
Antifogging agents in sticks and sprays are
also available, but vary in their effectiveness. Most
respirator manufacturers sell, but seldom advertise,
packages of thin plastic covers for protecting the
lens of a full-facepiece respirator. Available at a minimum
charge, these replaceable covers prevent
scratching of the permanent lens and prolong its life.
NIOSH-approved, air-purifying, full-facepiece respirators
for protection against particulate exposures
have the prefix TC-84A.
The minimum air flow rate for both a powered airpurifying
respirator and a continuous-flow, supplied-
air respirator with a half-facepiece or full
facepiece is 115 L/min. As with other continuousflow,
supplied-air respirators, the maximum air
flow for these devices may not exceed 425 L/min.
An air flow of 115 L/min is probably sufficient for
most work activities involving possible exposures
to aerosolized H. capsulatum spores. However,
breathing rates during activities requiring heavy
exertion may produce peak inhalation air flows
exceeding 115 L/min. Consequently, someone doing heavy work could intermittently overbreathe
the respirator's air flow, resulting in brief periods when contaminated air could enter the facepiece at gaps in the face-to-facepiece seal.
The full-facepiece respirators described in this section
are recommended as the minimum respiratory
protection in extremely dusty conditions where high
concentrations of H. capsulatum spores could be
aerosolized, especially in enclosed areas. Air-purifying,
full-facepiece respirators have been recommended
for poultry workers based on the results of
air sampling during chicken-catching activities
inside poultry houses.(103) As mentioned earlier,
half-facepiece respirators provide no eye protection,
and even the concurrent use of eyecup goggles is
probably impractical in extremely dusty working
conditions. Unless the results of quantitative tests
suggest that a person wearing an air-purifying, fullfacepiece
respirator can achieve an outstanding facepiece
seal, a powered air-purifying respirator with a
full facepiece should be chosen for extremely
dusty work.
A powered air-purifying respirator with a full facepiece
should also be the minimum respiratory protection
worn by someone entering an enclosed area
in which the amount of bat and bird manure contamination
is unknown. A less protective respirator
should be worn only when a site has been evaluated
as having a low risk for inhalation exposure to material
that might be contaminated with H. capsulatum.
Pressure-demand, supplied-air
respirators with full facepiece
(assigned protection factor: 2,000)
The air regulator of a pressure-demand, supplied-air
respirator is designed to maintain positive facepiece
pressure even during heavy physical activity. This
type of respirator has the same advantages and disadvantages
as other supplied-air respirators, except
that a vortex tube cannot be used to cool the air
delivered to the respirator wearer.
Pressure-demand, self-contained
breathing apparatuses (SCBA) and
combination pressure-demand, suppliedair
respirators with auxiliary SCBA
(assigned protection factor: 10,000)
Because the wearer of a self-contained breathing
apparatus (SCBA) carries his or her own air supply,
a pressure-demand SCBA has an advantage of
allowing greater mobility than a supplied-air respirator.
However, not everyone may agree that this is
a significant advantage, since these devices can
weigh as much as 40 pounds. Open-circuit SCBAs,
like those worn by firefighters, are available with
rated service lives of 15, 30, 45, and 60 minutes.
Auxiliary SCBAs for combination units are available
that have service lives ranging from 3 to 60
minutes. Closed-circuit SCBAs, like those worn by
members of mine rescue teams, are available with
rated service lives from 1 to 4 hours.
SCBAs have been recommended for use by
workers in areas contaminated with H. capsulatum spores,(100) but they are too impractical for most situations
where respirators are needed to protect
against the inhalation of H. capsulatum spores.
Another disadvantage, particularly during removal
jobs that may take a long time, is that SCBA can be
used for only 30 to 60 minutes. Thus, frequent work
stoppages are needed to change air cylinders. Also,
an adequate supply of full cylinders is
needed at a work site.
Combination pressure-demand, supplied-air respirators
with auxiliary SCBA would be useful for very
dusty work environments. The auxiliary SCBA
could be used to escape to an area of fresh air whenever
delivery of breathing air is interrupted. All
NIOSH-approved SCBA and combination SCBA
and supplied-air respirators have the prefix TC-13F.
Summary
Because of the need for mobility, most decisions
concerning the appropriate respirator for protecting
against inhalation exposure to material that might
contain H. capsulatum spores will involve choosing
the most appropriate air-purifying respirator. To
help the reader with this decision, Table 1 summarizes
the advantages and disadvantages of air-purifying
respirators and their costs.
Disposable protective clothing and shoe coverings
should be worn whenever regular work clothing and shoes might be contaminated with dust containing
H. capsulatum spores.(44,57,58) Wearing such clothing
can reduce or eliminate the likelihood of transferring
spore-contaminated dust to places away from
a work site, such as a car or home. When spore-contaminated
material is likely to fall from overhead,
workers should wear disposable protective clothing
with hoods.(58) Workers should wear disposable
shoe coverings with ridged soles made of slip-resistant
material to reduce the likelihood of slipping on
wet or dusty surfaces. After working in a spore-contaminated
area and before removing respirators,
workers should remove all protective clothing and
shoe coverings and seal them in heavy-duty plastic
bags to be disposed of in a landfill.(120)
Since the personal protective equipment described
above can be more insulating than regular work
clothing, sweat evaporation may be impeded during
some work activities. Therefore, precautions may
need to be taken to control heat stress. For example,
when protective clothing is needed, wearing a lightweight,
cotton coverall would create less of a heatstress
risk for a worker than wearing a chemicalresistant
suit. Additionally, workers should know
the symptoms of heat-stress-related illnesses and be
able to take appropriate measures to ensure that
such illnesses do not occur. Some jobs may have
such a significant risk of heat stress that they should
be scheduled only when ambient temperatures are
relatively cool.
Wearing chemical-resistant gloves will seldom be
necessary when working in a spore-contaminated
area. If they are worn, care should be taken to avoid
the harmful effects on the skin that can result from
occlusion (physical process of trapping a material
against the skin), sweating, and maceration (softening
and breaking down of tissue).(121,122) A thin cotton
glove can be worn inside a chemical-resistant
glove to protect against dermatitis, which can occur
from prolonged skin exposure to moisture in gloves
caused by perspiration. Because wearing chemicalresistant
gloves can aggravate existing dermatitis,
their use by workers having dermatitis may not be
appropriate. The medical treatment of workers having dermatitis and decisions about their use of
gloves should be supervised by a physician experienced
with occupational skin diseases.(122)
Table 1. Air-Purifying Respirators
Respirator type |
NIOSH assigned protection factor(106) |
Advantages |
Disadvantages |
Cost (2004 dollars) |
Filtering facepiece (Disposable) |
10 |
- lightweight - no maintenance or cleaning needed - no effect on mobility |
- provides no eye protection - can add to heat burden - inward leakage at gaps in face seal - some do not have adjustable head straps - difficult for a user to do a seal check - level of protection varies greatly among models - communication may be difficult - fit testing required to select proper facepiece size - some eyewear may interfere with the fit |
$0.70 to $10 |
Elastomeric half-facepiece |
10 |
- low maintenance - reusable facepiece and replaceable filters and cartridges - no effect on mobility |
- provides no eye protection - can add to heat burden - inward leakage at gaps in face seal - communication may be difficult - fit testing required to select proper facepiece size - some eyewear may interfere with the fit |
facepiece: $12 to $35 filters: $4 to $8 each |
Powered with loose-fitting facepiece |
25 |
- provides eye protection - protection for people with beards, missing dentures or facial scars - low breathing resistance - flowing air creates cooling effect - face seal leakage is generally outward - fit testing is not required - prescription glasses can be worn - communication less difficult than with elastomeric half-facepiece or full-facepiece respirators - reusable components and replaceable filters |
- added weight of battery and blower - awkward for some tasks - battery requires charging - air flow must be tested with flow device before use |
unit: $400 to $1000 filters: $10 to $30 |
Elastomeric full-facepiece with N-100, R-100, or P-100 filters |
50 |
- provides eye protection - low maintenance - reusable facepiece and replaceable filters and cartridges - no effect on mobility - more effective face seal than that of filtering facepiece or elastomeric half-facepiece respirators |
- can add to heat burden - diminished field-of-vision compared to half-facepiece - inward leakage at gaps in face seal - fit testing required to select proper facepiece size - facepiece lens can fog without nose cup or lens treatment - spectacle kit needed for people who wear corrective glasses |
facepiece: $90 to $240 filters: $4 to $8 each nose cup: $30 |
Powered with tight-fitting half-facepiece or full-facepiece |
50 |
- provides eye protection with full-facepiece - low breathing resistance - face seal leakage is generally outward - flowing air creates cooling effect - reusable components and replaceable filters |
- added weight of battery and blower - awkward for some tasks - no eye protection with half-facepiece - fit testing required to select proper facepiece size - battery requires charging - communication may be difficult - spectacle kit needed for people who wear corrective glasses with full face-piece respirators - air flow must be tested with flow device before use |
unit: $500 to $1000 filters: $10 to $30 |
Note: The assigned protection factors in this table are from the NIOSH Respirator Selection Logic.(106) When the table was prepared, OSHA had proposed amending the respiratory protection standard to incorporate assigned protection factors.(107) The Internet sites of NIOSH (
www.cdc.gov/niosh) and OSHA (
www.osha.gov) should be checked for the current assigned protection factor values.
In addition to H. capsulatum, inhalation exposure to
Cryptococcus neoformans may also be a health risk
for workers in environments containing accumulations
of bat droppings or bird manure. Inhalation
exposures to Chlamydia psittaci have occurred
occasionally in environments containing the
manure of certain birds, and exposure to the rabies
virus is a health risk for workers who must handle
dead bats.
Cryptococcus neoformans
C. neoformans is the infectious agent of the fungal
disease cryptococcosis. Formerly a rare disease, the
incidence of cryptococcosis has increased in recent
years because of its frequent occurrence in AIDS
patients.(123-127) C. neoformans and H. capsulatum are only two of the more than 100 microorganisms that have been reported with increased frequency among HIV-infected persons, and cryptococcosis and histoplasmosis are both classified as AIDSindicator opportunistic infectious diseases.(127) In 1997, the USPHS/IDSA Prevention of Opportunistic Infections Working Group recommended that HIVinfected persons should avoid "sites that are likely to be heavily contaminated with C. neoformans (e.g., areas heavily contaminated with pigeon droppings)."( 128) However, evidence is lacking that contaminated bird manure is the primary environmental source of exposure to C. neoformans in most cases of cryptococcosis among HIV-infected persons.( 125) Thus, the 2001 USPHS/IDSA guidelines do not include the pigeon droppings example.(89) An HIV-infected person should consult his or her health care provider about the appropriate exposure precautions to be taken for any activity having a risk of exposure to C. neoformans.
C. neoformans uses the creatinine in avian feces as
a nitrogen source. It gains a competitive advantage
over other microorganisms and multiplies exceedingly
well in dry bird manure accumulated in places
that are not in direct sunlight.(38,123) This microorganism
is commonly associated with old pigeon
manure, but it has also been recovered from dried
excreta of chickens, sparrows, starlings, and other
birds.(123) As with H. capsulatum, C. neoformans
has not been found in fresh bird droppings, but it
has been cultured from the beaks and feet of
pigeons.(123) Bats have been shown to be infected
with C. neoformans,(129) and both C. neoformans
and H. capsulatum have been recovered from bat
dropping samples collected at the same site.(66,67)
However, it should not be assumed that a worker's illness is cryptococcosis when only C. neoformans is recovered from environmental samples collected from suspected sources of exposure. C. neoformans has been recovered from environments where H. capsulatum was not recovered, even though sick workers were diagnosed from the results of clinical tests as having histoplasmosis.(61,86)
Unlike outbreaks of other mycoses, outbreaks of cryptococcosis traced to environmental sources have not been described, and it is presumed that most people can overcome most inhalation exposures to C. neoformans.(124) More detailed information about C. neoformans and cryptococcosis is available in other reports.(123,124,130-133) Work practices described previously in this document for controlling exposures to H. capsulatum, including the use of personal protective equipment, will also protect against inhalation exposures to C. neoformans and other microorganisms.
Chlamydia psittaci
Psittacosis is caused by a bacterium (C. psittaci)
rather than a fungus, but it is another infectious disease
that people can develop after disturbing and
inhaling contaminated bird manure. While
C. psittaci has been isolated from approximately
130 avian species,(134) most human infections result
from inhalation exposures to aerosolized urine, respiratory secretions, or dried manure of infected
psittacine (parrot-type) birds, such as cockatiels,
parakeets, parrots, and macaws; avian chlamydiosis
is diagnosed less frequently in canaries and
finches.(135) Among caged, nonpsittacine birds,
infection with C. psittaci occurs most frequently in
pigeons, doves, mynah birds. Psittacosis in humans
has occasionally been associated with exposures to
infected pigeons, turkeys, chickens, ducks, pheasants,
and geese, or their manure.(83,134,136-138)
According to the CDC's annual summaries of notifiable diseases, 904 cases of psittacosis in humans were reported to CDC from 1988 through 2003 (range: 15 cases in 2003 to 116 cases in 1989). Psittacosis is not a notifiable disease in all states, and thus, the actual number of cases is likely to be higher. Also, the number of cases may be underestimated because the disease is difficult to diagnose and cases often go unreported.(135) The severity of disease experienced by an infected person can range from asymptomatic to severe systemic disease with pneumonia; death occurs in less than 1% of properly treated patients.(135)
The National Association of State Public Health
Veterinarians has recommended that workers
should wear protective clothing, gloves, and a respirator
with filters having an N-95 rating or higher
when cleaning cages or handling birds infected with
C. psittaci.(135)
Rabies
Rabies is a viral disease caused by infection of the
central nervous systems of wild and domestic animals
and humans.(139) The initial symptoms of
human rabies resemble those of other systemic viral
infections, including fever, headache, malaise, and
disorders of the upper respiratory and gastrointestinal
tracts.(140) Recognizing that a person has been
exposed to the virus and prompt treatment are
essential for preventing rabies. For once clinical
symptoms have begun, there is no treatment for
rabies and almost all patients will die from the disease
or its complications within a few weeks of
onset.(139,140)
In the United States, wild animals (especially bats,
raccoons, skunks, coyotes, and foxes) are the most
important sources of rabies infection.(141-143) Indigenous rabid bats have been reported from every state except Hawaii.(141-143) Individual bats from most of the estimated 41 bat species in the United States have been found to be infected with rabies virus.(145) Rabies virus associated with insectivorous bats (those that feed principally on insects) accounted for 32 of the 35 indigenous rabies cases in humans in the United States between 1958 and 2000.(145)
Rabies is transmitted via an infected animal's bite or by contamination of abrasions, open wounds, mucous membranes or theoretically, scratches, by infectious material such as saliva.(144) Contact with the blood, urine, or manure of a rabid animal is not a risk factor for contracting rabies.(144) Consequently, workers exposed to accumulations of bat droppings in environments from which bats have been excluded have no rabies risk. Although spelunkers seldom have direct contact with bats, they are included in a frequent-risk category by CDC because of potential for bite, nonbite, or aerosol exposure to the rabies virus.(144) Two fatal cases of rabies in humans have been attributed to possible airborne exposures in caves containing millions of free-tailed bats.(144) In addition, between 1990 and 2000, a bite was documented in only 2 of the 24 U.S. human rabies cases caused by bat-associated rabies virus variants.(146) This suggests "that transmission of rabies virus can occur from minor, seemingly unimportant, or unrecognized bites from bats."(144) While aerosol transmission of the rabies virus from bats to people is theoretically possible under extraordinary conditions, the risk is otherwise negligible.
The percentage of rabid bats in any colony is probably
low (0.5% or less(95)). However, a dead bat
should still never be picked up with bare hands
since its death may have been caused by an infectious
agent. The rabies virus can remain infectious in
a carcass until decomposition is well advanced.(94)
Thus, whenever possible, a shovel or some other tool should be used to pick up and dispose of a dead
bat. If a dead bat must be handled, wearing heavy
work gloves should minimize the risk of disease
transmission because of an accidental scratch from
the bat's teeth or by contamination of existing scratches or abrasions on a worker's hands.
This guidance document was prepared by the
National Institute for Occupational Safety and
Health (NIOSH) and the National Center for Infectious Diseases (NCID), both of the Centers for
Disease Control and Prevention. For more information
about histoplasmosis or other infectious diseases,
please contact your physician, your local
health department, or NCID in Atlanta, Georgia,
NCID's Internet address is
http://www.cdc.gov/ncidod/. For more information about worker health and safety precautions during disturbances of soil, bat droppings, or bird manure that might be contaminated with H. capsulatum spores, call NIOSH in Cincinnati, Ohio, at (800) 356-4674. A list of nonpowered, air-purifying respirators that have been tested and approved by NIOSH under 42 CFR Part 84 regulations can be found on the NIOSH Internet home page,
http://www.cdc.gov/niosh.
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HISTOPLASMOSIS
What is histoplasmosis?
Histoplasmosis is an infectious disease caused by
inhaling spores of a fungus called Histoplasma
capsulatum. Histoplasmosis is not contagious; it
cannot be transmitted from an infected person or
animal to someone else.
What are the symptoms of histoplasmosis?
Histoplasmosis primarily affects a person's lungs, and its symptoms vary greatly. The vast majority of infected people are asymptomatic (have no apparent ill effects) or they experience symptoms so mild they do not seek medical attention. If symptoms do occur, they will usually start within 3 to 17 days after exposure, with an average of 10 days. Histoplasmosis can appear as a mild, flu-like respiratory illness and has a combination of symptoms, including malaise (a general ill feeling), fever, chest pain, dry or nonproductive cough, headache, loss of appetite, shortness of breath, joint and muscle pains, chills, and hoarseness. A chest X-ray of a person with acute pulmonary histoplamosis will commonly show a patchy pneumonitis, which eventually calcifies. Chronic lung disease due to histoplasmosis resembles tuberculosis and can worsen over months or years. The most severe and rare form of this disease is disseminated histoplasmosis, which involves spreading of the fungus to other organs outside the lungs.
Who can get histoplasmosis?
Anyone working at a job or present near activities where material contaminated with H. capsulatum becomes airborne can develop histoplasmosis if enough spores are inhaled. After an exposure, how ill a person becomes varies greatly and most likely depends on the number of spores inhaled and a person's age and susceptibility to the disease. The number of inhaled spores needed to cause disease is unknown. Children younger than 2 years of age, persons with compromised immune systems, and older persons, in particular those with underlying
illnesses such as diabetes and chronic lung disease,
are at increased risk for developing symptomatic
histoplasmosis.
People with weakened immune systems are at greatest
risk for developing severe and disseminated
histoplasmosis. Included in this high-risk group are
persons with AIDS or cancer and persons receiving
cancer chemotherapy; high-dose, long-term steroid
therapy; or other immuno-suppressive drugs.
Before 2000, a person could learn from a histoplasmin
skin test whether he or she had been previously
infected by H. capsulatum. However, the
manufacturing of histoplasmin was discontinued in
2000, and the skin testing reagents were still
unavailable in 2004. A previous infection can provide
partial immunity to reinfection. Since a positive
skin test does not mean that a person is completely
immune to reinfection, appropriate exposure
precautions should be taken regardless of a
worker's past skin-test status whenever disturbances of materials that might be contaminated with H. capsulatum occur.
What is the treatment for histoplasmosis?
Mild cases of histoplasmosis are usually resolved
without treatment. For severe cases, special antifungal
medications are needed to arrest the disease.
Disseminated histoplasmosis is fatal if untreated,
but death can also occur in some patients even
when medical treatment is received.
Where are H. capsulatum spores found?
H. capsulatum grows in soils throughout the world.
In the United States, the fungus is endemic (more
prevalent) and the proportion of people infected by
H. capsulatum is higher in central and eastern
states, especially along the Ohio and Mississippi
River valleys. The fungus seems to grow best in
soils having a high nitrogen content, especially those enriched with bat droppings or bird manure.
Disturbances of contaminated material cause small
H. capsulatum spores to become airborne or
aerosolized. Once airborne, spores can easily be carried
by wind currents over long distances.
How can someone know if soil or
droppings are contaminated with
H. capsulatum spores?
To learn whether soil or droppings are contaminated
with H. capsulatum spores, samples must be collected
and cultured. Presently, the method used to isolate
H. capsulatum is expensive and requires several
weeks to complete. If not enough samples are
collected, small but highly contaminated areas can
be overlooked. Until a less expensive and more
rapid method is available, testing samples for
H. capsulatum will continue to be impractical for
most situations. Consequently, when thorough testing
is not done, the safest approach is to assume soil
in endemic regions and any accumulations of bat
droppings or bird manure are contaminated with
H. capsulatum and take appropriate exposure
precautions.
What jobs and activities have risks for exposure to H. capsulatum spores?
Below is a partial list of occupations and hobbies
with risks for exposure to H. capsulatum spores.
Appropriate exposure precautions should be taken
by these people and others whenever contaminated
soil, bat droppings, or bird manure is disturbed.
- Bridge inspector or painter
- Chimney cleaner
- Construction worker
- Demolition worker
- Farmer
- Gardener
- Heating and air-conditioning system installer or service person
- Microbiology laboratory worker
- Pest control worker
- Restorer of historic or abandoned buildings
- Roofer
- Spelunker (cave explorer)
How can exposure to H. capsulatum be controlled and histoplasmosis prevented?
The best way to prevent exposures to H. capsulatum
spores is to avoid situations where material that
might be contaminated can become aerosolized and
subsequently inhaled. This is especially important
for persons with weakened immune systems.
Dust suppression methods, such as carefully wetting
with a water spray, may be useful for reducing the
amount of material aerosolized during an activity.
For some activities, such as removing an accumulation
of bat droppings or bird manure from an
enclosed place such as an attic, wearing a
NIOSH-approved respirator and other items of personal
protective equipment may be needed to further
reduce the risk of H. capsulatum exposure. However,
only persons trained in the proper selection and use
of personal protective equipment should undertake
work where this equipment is needed.
Disinfectants have occasionally been used to treat
soil and accumulated bat manure when removal was
impractical or as a precaution before a removal
process was started. There is no product or chemical
that is registered by the EPA that has the specific
claim of being effective against H. capsulatum. A
manufacturer of a product claiming to disinfect soil
contaminated with H. capsulatum will have to meet
the EPA's regulatory requirements and complete the registration process.
Where can I get more information
about histoplasmosis?
This histoplasmosis fact sheet was prepared by the
National Institute for Occupational Safety and Health
(NIOSH) and the National Center for Infectious
Diseases (NCID), both of the Centers for Disease
Control and Prevention. For answers to other questions
about histoplasmosis or histoplasmin skin-testing,
please contact your physician, your local health
department, or NCID in Atlanta, Georgia. NCID's Internet address is
http://www.cdc.gov/ncidod/. For other questions about worker health and safety precautions during disturbances of soil, bat droppings, or bird manure that might be contaminated with H. capsulatum spores, call NIOSH in Cincinnati, Ohio, at (800) 356-4674.
HISTOPLASMOSIS
¿Qué es la histoplasmosis?
La histoplasmosis es una enfermedad infecciosa causada por la inhalación de esporas de un hongo llamado Histoplasma capsulatum. La histoplasmosis no es contagiosa; no puede ser transmitida de una persona o animal enfermo a alguien sano.
¿Cuales son los síntomas de la histoplasmosis?
La histoplasmosis afecta principalmente los pulmones y sus síntomas son muy variables. La gran mayoría de las personas infectadas son asintomáticas (no tienen efectos aparentes de enfermedad) o presentan síntomas tan leves que no requieren atención médica. Cuando hay síntomas, éstos generalmente empiezan 3 a 17 días después de la exposición, con un promedio de 10 días. La histoplasmosis puede aparecer como una enfermedad respiratoria leve tipo influenza y tiene una combinación de síntomas que incluyen decaimiento (sensación de enfermedad), fiebre, dolor en el pecho, tos seca o no productiva, dolor de cabeza, pérdida de apetito, disnea (dificultad para respirar), dolores musculares y de articulaciones, calofríos y ronquera. Una radiografía de tórax de una persona con histoplasmosis pulmonar aguda muestra con frecuencia una neumonitis desigual que se calcifica eventualmente. La enfermedad pulmonar crónica por histoplasmosis se parece a la tuberculosis y puede empeorar a través de los meses o años. La forma más severa y rara de esta enfermedad es la histoplasmosis diseminada, que involucra la invasión del hongo a otros órganos fuera de los pulmones.
¿Quién puede contraer histoplasmosis?
Cualquier persona que trabaje o esté presente cerca de actividades en donde el material contaminado con H. capsulatum se haga volátil, puede desarrollar histoplasmosis si inhala suficientes esporas. Después de una exposición, la severidad de la enfermedad es muy variable y probablemente dependa del número de esporas inhaladas y de la edad y susceptibilidad de la persona a contraer la enfermedad. El número de esporas que es necesario inhalar para contraer la enfermedad es desconocido. Los niños menores de dos años, las personas con sistemas inmunes comprometidos y los adultos mayores, en particular aquellos con enfermedades subyacentes tales como diabetes y enfermedad pulmonar crónica, tienen un mayor riesgo de desarrollar histoplasmosis sintomática.
Las personas con deficiencias del sistema inmune sufren mayor riesgo de desarrollar histoplasmosis severa y diseminada. Incluidos en este grupo de alto riesgo se encuentran las personas con SIDA o cáncer y las personas que están recibiendo quimioterapia, terapia con altas dosis de esteroides por tiempo prolongado o terapia con otros medicamentos inmunosupresores.
Antes del año 2000, una persona podía saber si había sido infectada previamente con H. capsulatum a través de una prueba cutánea con histoplasmina. Sin embargo, la fabricación de histoplasmina se descontinuó en 2000, y los reactivos para hacer la prueba cutánea seguían sin estar disponibles en el 2004. Una infección previa puede otorgar inmunidad parcial contra una reinfección. Dado que una prueba cutánea positiva no significa que una persona sea completamente inmune a una reinfección, deben ser adoptadas medidas apropiadas de protección contra la exposición. Estas medidas deberán ser adoptadas, independientemente de los resultados de la prueba cutánea, por aquellos trabajadores que manipulen materiales que puedan estar contaminados con H. capsulatum.
¿Cúal es el tratamiento de la histoplasmosis?
Los casos leves de histoplasmosis usualmente se resuelven sin tratamiento. Los casos severos requieren medicamentos especiales antihongos (fungicidas) para controlar la enfermedad. La histoplasmosis diseminada es mortal si no se trata, pero la muerte también puede ocurrir aún cuando se reciba tratamiento médico.
¿Dónde se encuentran las esporas de H. capsulatum?
El H. capsulatum se encuentra en suelos de todo el mundo. En los Estados Unidos, el hongo es endémico (más prevalente) y la proporción de gente infectada por H. capsulatum es mayor en los estados del este y el centro, sobre todo a lo largo de los valles de los ríos Ohio y Mississippi. El hongo parece crecer mejor en suelos con alto contenido de nitrógeno, especialmente aquellos enriquecidos con guano de murciélago o estiércol de pájaro. La manipulación de material contaminado hace que las pequeñas esporas de H. capsulatum se hagan volátiles o se conviertan en aerosol. Una vez volátiles, las esporas pueden ser fácilmente transportadas por corrientes de viento a grandes distancias.
¿Cómo se puede saber si el suelo o el guano están contaminadas con esporas de H. capsulatum?
Para saber si el suelo o el guano están contaminados con esporas de H. capsulatum, se deben tomar muestras para cultivo. Actualmente, el método usado para aislar H. capsulatum es caro y requiere varias semanas para completarlo. Si no se toman suficientes muestras, pueden ignorarse áreas pequeñas pero muy contaminadas. Hasta que exista un método más rápido y menos caro, el examen de muestras seguirá siendo poco práctico en la mayoría de las situaciones. En consecuencia, cuando no se hace un examen extensivo, el enfoque más seguro es asumir que el suelo en regiones endémicas y cualquier acumulación de guano de murciélago o estiércol de pájaro, están contaminados con H. capsulatum y, por lo tanto, tomar las medidas necesarias para prevenir la exposición.
¿Qué trabajos y actividades tienen riesgo de exposición a H. capsulatum?
A continuación hay una lista parcial de ocupaciones y pasatiempos que tienen riesgo de exposición a esporas de H. capsulatum. Estas personas deben tomar medidas adecuadas para prevenir la exposición siempre que se manipule suelo contaminado, guano de murciélago o estiércol de pájaro.
- Inspector o pintor de puentes
- Limpiador de chimeneas
- Trabajador de la construcción
- Trabajador de demolición
- Granjero, trabajador agrícola
- Jardinero
- Instalador o agente de servicio de sistemas de aire acondicionado y calefacción
- Trabajador de laboratorio microbiológico
- Trabajador de control de plagas
- Restaurador de edificios históricos o abandonados
- Trabajador de techos
- Explorador de cuevas
¿Cómo se puede controlar la exposición a H. capsulatum y prevenir la histoplasmosis?
La mejor forma de prevenir la exposición a las esporas de H. capsulatum es evitar aquellas situaciones donde materiales contaminados puedan hacerse volátiles y las esporas ser posteriormente inhaladas. Esto es importante sobre todo para aquellas personas con depresión del sistema inmune.
Los métodos de supresión de polvo, tal como humedecer cuidadosamente con un aspersor de agua, pueden ser útiles para reducir la cantidad de material que se volatiliza durante una actividad. Para algunas actividades, tales como remover una acumulación de guano de murciélago o estiércol de pájaro de un lugar cerrado, cómo un ático, se debe usar un respirador aprobado por NIOSH. Otros artículos de protección personal pueden ser necesarios para disminuir el riesgo de exposición a H. capsulatum. Sin embargo, sólo las personas capacitadas en la selección y el uso adecuados del equipo de protección personal deben llevar a cabo actividades donde este equipo sea requerido.
Ocasionalmente se han usado desinfectantes para
tratar el suelo y la acumulación de guano de murciélago, cuando la remoción no es práctica, o como una precaución antes de iniciar el proceso de remoción. No existe producto o agente químico registrado por la EPA (Agencia de Protección Ambiental) que sea efectivo contra H. capsulatum. El fabricante de algún producto que afirme que desinfecta el suelo contaminado con H. capsulatum tendrá que cumplir con los requisitos regulatorios de la EPA y completar el proceso de registro.
¿Dónde se puede obtener más información sobre la histoplasmosis?
Esta hoja informativa sobre la histoplasmosis fue preparada por el Instituto Nacional de Salud y Seguridad Ocupacional (NIOSH) y el Centro Nacional de Enfermedades Infecciosas (NCID), ambos de los Centros de Control y Prevención de Enfermedades. Para respuestas a otras preguntas sobre histoplasmosis, por favor contacte a su médico, a su departamento de salud local, o al NCID en Atlanta, Georgia. La dirección de Internet del NCID es
http://www.cdc.gov/ncidod/. Para otras consultas sobre la salud de los trabajadores y medidas de precaución a usar durante la manipulación de suelo, guano de murciélago o estiércol de pájaro potencialmente contaminados con esporas de H. capsulatum, llame a NIOSH en Cincinnati, Ohio, al teléfono (800) 356-4674