2005 - Histoplasmosis
*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2005
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.
In 2005, 110 confirmed cases of histoplasmosis were reported in Indiana for an incidence rate of 1.75 cases per 100,000 population (Table 1). This represents almost a 100 percent increase from 2004 (0.88). An outbreak of histoplasmosis contributed to the large increase. Figure 1 illustrates the number of cases by year for 2001-2005. Histoplasmosis occurred throughout the year in 2005 with the largest number of cases occurring in the winter and early spring months (Figure 2). Figure 3 displays the distribution of cases by age group. Age-specific rates were greatest among adults aged 30-69 years of age. Males (1.91) were more likely to be reported with histoplasmosis infection than females (1.60).
In 2005, 41 counties reported at least 1 case of histoplasmosis in Indiana. The incidence rates were highest among the following counties reporting five or more cases: Montgomery (13.1), Delaware (6.9), and Hamilton (2.9). Figure 4 shows counties reporting five or more cases of histoplasmosis in 2005.
One outbreak of histoplasmosis occurred in Indiana in 2005. The outbreak occurred among a missionary group that traveled to Mississippi in April 2005. Of the 21 people who traveled, 11 developed some level of illness. The infectious agent identified was histoplasma capsulatum, which is typically found as a mold in the soils and yeast in animals and humans. The average incubation period is 3-17 days after exposure, with the average being 10 days. None of the cases required advanced anti-fungal treatment for the illness, and most resolved without any treatment.
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