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

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What are the advantages and disadvantages of various kinds of respirators for protecting workers against exposure to H. capsulatum?

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 one-tenth (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-to-facepiece 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 fixed-length 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 negative-pressure 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 full-facepiece 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 air-purifying respirator and a continuous-flow, supplied-air respirator with a half-facepiece or full facepiece is 115 L/min. As with other continuous-flow, 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, full-facepiece 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, supplied-air 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.

What personal protective equipment other than respirators should workers wear?

Disposable protective clothing and shoe coverings should be worn whenever regular work clothing and shoes might be contaminated with dust containing H. capsulatum spores. ^{(44,5 7,58)} 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 light-weight, cotton coverall would create less of a heat-stress risk for a worker than wearing a chemical-resistant 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 chemical-resistant 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

What other infectious agents are health risks for workers who disturb accumulations of bat droppings or bird manure?

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 AIDS-indicator opportunistic infectious diseases. ⁽¹²⁷⁾ In 1997, the USPHS/IDSA Prevention of Opportunistic Infections Working Group recommended that HIV-infected 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 under-estimated 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.

Where can I get more information about infectious diseases and answers to questions about worker health and safety issues?

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 non-powered, 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.

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