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NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

6.5 Histoplasmosis

previous 6.4 Understanding the Effect and Mechanisms of Occupational Exposures on Pulmonary Susceptibility to Infection | 6.6 RDRP Publications of Special Note Relating to Infectious Diseases next

Over the past 25 years, RDRP scientists have investigated seven documented outbreaks of histoplasmosis among workers. The main cause to be a lack of worker and employer awareness regarding: the health risks of exposure to Histoplasma capsulatum; the type of activities which could cause an exposure; and methods to protect workers and others from being exposed. RDRP efforts in this area have been to educate workers and employers on the environments where histoplasmosis may occur and steps to prevent infection. These efforts have led to recommendations designed to reduce the incidence of occupational histoplasmosis.


 Workers may develop Histoplasmosis when they inhale spores or hyphae of the soil-borne fungus, H. capsulatum. Histoplasmosis is not transmissible from person to person but occurs when soil or dust containing the fungus is disturbed and inhaled. This fungus is endemic in the U.S., with most of the documented infections occurring in central and eastern states, particularly in the Ohio and Mississippi River valleys. Soil and dust from areas where birds or bats roost are particularly prone to contain the fungus, as the animal droppings increase the nitrogen content of the soil and allow the fungus to proliferate (A6-114).

The first documented cases of occupational histoplasmosis in the U.S. occurred in a 1938 outbreak among 23 Works Progress Administration workers removing pigeon droppings from a schoolhouse in Plattsburgh, New York (A6-115).179 A search of the scientific literature from 1938 to the present found 35 reports of occupational histoplasmosis in either individual or groups of U.S. workers. From these, RDRP scientists identified occupations at risk of histoplasmosis: bridge inspectors or painters; chimney cleaners; construction workers; demolition workers; farmers; gardeners; heating and air conditioning installer or service persons; microbiology laboratory workers; pest control workers; restorers of historic or abandoned buildings; roofers. Histoplasmosis has also been documented in workers incidentally exposed either downwind of soil-disturbing activities or through airborne soil particles entrained in building ventilation systems. It is likely that many of these infections could have been prevented if the potential for exposure had been identified and the proper precautions implemented.


 RDRP efforts in this area have been to conduct HHEs on histoplasmosis exposure and to educate workers and employers on the environments where H. capsulatum may occur and on the proper steps to take when dusts or soils potentially containing the fungus are disturbed. RDRP scientists, in conjunction with others from NCID, developed a guidance document entitled “Histoplasmosis: Protecting Workers at Risk,” disseminated by NISOH in 1997 and (in a revised form) in 2004 (A6-114).

In addition, RDRP scientists have developed a PCR method that has reduced the analysis time for detecting H. capsulatum in soil samples from many weeks to just two days (19, A6-116).

Outputs and Transfer

 RDRP transferred its research results on histoplasmosis to others through: two HHE reports (A6-117, A6-118), two peer-reviewed scientific papers (20, 21, A6-119, A6-120), one industry trade journal paper (A6-121), a English and Spanish Fact Sheet (A6-122, A6-123), a MMWR article, (A6-124) three presentations at conferences and meetings (A6-125, A6-126, A6-127), and one NIOSH numbered document (A6-114).

Intermediate Outcomes

The NIOSH recommendations on preventing histoplasmosis have been adopted by other agencies and organizations, including: Laborers’ Health and Safety Fund of North America (A6-128); Clemson University Research Medical Surveillance Program (A6-129); Defense Supply Center Richmond, Defense Logics Agency, Hazardous Technical Information Services (A6-130); StaffScapes Professional Employer Organization (A6-131); Korean Radiological Society (A6-132); and New Jersey Department of Health and Senior Services, Division of Epidemiology, Environmental, and Occupational Health, Public Employees Occupational Safety and Health Program (A6-133). The new RDRP NIOSH publication on protecting workers against histoplasmosis is cited on the OSHA Respiratory Protection Hazard Recognition Web page (A6-134). The CPWR electronic library of construction occupational safety and health replicates verbatim “Histoplasmosis: Protecting Workers at Risk” (revised edition) in both English and Spanish (A6-135, A6-136).

 What’s Ahead

This is a mature area of study. No new RDRP research in this area is planned or anticipated at this time, though we intend to continue dissemination of relevant information to prevent outbreaks of occupational histoplasmosis by maintaining awareness. New initiatives would only be undertaken should recurrence or worsening of the problem occur as documented through surveillance or by disease outbreaks.

Strategic and Intermediate Goals Moving Forward

 The RDRP strategic goal is to prevent and reduce occupational respiratory infectious diseases.

To achieve this strategic goal, the following intermediate goals have been developed:

  • Maintain reductions in occupational TB incidence in high-risk work settings
  • Protect workers from bioterrorism agents
  • Protect workers from occupational acquisition of emerging diseases (including SARS, avian and pandemic flu)
  • Protect workers from occupational exposures making them susceptible to respiratory infections
  • Prevent outbreaks of occupational histoplasmosis by maintaining worker and employer awareness

179. Daniel TM, Bain GL [2002]. Epidemics are for the Birds—and Bats.  In Drama and Discovery: the Story of Histoplasmosis. Westport, CT: Greenwood Press pp.77-83.