NIOSH Publication No. 2005-109: Histoplasmosis — Protecting Workers at Risk	December 2004

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Who can get histoplasmosis and what jobs and activities put people at risk for exposure to H. capsulatum spores?

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 HIV-infected 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 laboratory-confirmed 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.

Should workers who might be exposed to H. capsulatum have pre-exposure skin or blood tests?

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)

What can be done to reduce exposures to H. capsulatum?

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.

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 landfill 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 air-conditioning (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.

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