*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2002
Histoplasmosis is caused by Histoplasma capsulatum, a saprophytic soil fungus. The primary route of transmission is inhalation of infectious spores made airborne by the disturbance of contaminated soil. The presence of Histoplasma capsulatum has been associated with soil enriched with bird feces especially blackbirds, starlings, chickens, and pigeons. However, birds are not carriers of histoplasmosis, but accumulation of bird feces provide the organic enrichment needed for Histoplasma growth. Bat guano may also carry the organism.
Approximately 90 percent of Histoplasma capsulatum infections are asymptomatic. Clinically recognized histoplasmosis can be characterized into one of three forms: 1) acute, pulmonary histoplasmosis; 2) disseminated histoplasmosis; and 3) chronic, cavitary histoplasmosis. Symptoms of acute cases are flu-like with nonproductive cough, chest pains, and difficult breathing. More severe disease may result in fever, night sweats, weight loss, and bloody sputum. Severe cases may result in Histoplasma organisms being disseminated to many body organs.
Histoplasmosis cases may occur as sporadic individual cases or as large outbreaks such as the 355 cases that occurred at an Indiana high school in 2001 (case numbers for this outbreak are not included in this discussion). At least one other large histoplasmosis outbreak was recorded previously in Indiana. A thorough review of both outbreaks is presented in the following citations:
A Large Urban Outbreak of Histoplasmosis: Clinical Features, Lawrence Joseph Wheat, et al, Annals of Internal Medicine, 1981: 94:331-337
A Large Histoplasmosis Outbreak Among High School Students in Indiana, 2001, Shadi Chamany, et al, The Pediatric Infectious Disease Journal, Oct 2004, Vol 23. No. 10, 909 – 914.
In 2002, 80 confirmed cases were reported in Indiana for a crude incidence rate of 1.30/100,000 population (Table 1). Figure 1 illustrates the number of cases by year from 1998 through 2002. Histoplasmosis occurred throughout the year in 2002 with the largest number of cases in early spring and fall (Figure 2). Figure 3 displays the distribution of cases by age group. Age-specific rates were greatest among adults between 30 and 59 years of age. Males (1.36) were slightly more likely to be reported with histoplasmosis infection than females (1.24).
The incidence rates were highest in the following counties reporting five or more cases:
Shelby (16.0) and Hendricks (7.9). Figure 4 shows Indiana counties reporting five or more cases.
You can learn more about histoplasmosis by visiting the following Web site:
CDC website: Histoplasmosis