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Indiana Epidemiology Newsletter
ISDH Field Epidemiologist, District 3
On July 16, 2007, a representative of the Auburn Family Practice contacted the Dekalb County Health Department (DCHD) to report that several people developed symptoms of respiratory-type illness after returning from a mission trip to Nicaragua. Members of the group had manually dug trenches for new home construction.
The Indiana State Department of Health (ISDH) and DCHD initiated a collaborative investigation to describe the outbreak and to identify cases of illness. The DCHD obtained a list of all members of the mission group and conducted interviews to determine who had become ill. All members of the group indicated they were aware of the probable diagnosis of histoplasmosis and what symptoms to observe. A confirmed case was defined as a previously healthy person who became ill after returning from the mission trip to Nicaragua and had laboratory confirmation of histoplasmosis. A probable case was defined as a previously healthy person who became ill after returning from the mission trip and had confirmed pulmonary infiltrates from chest x-ray but did not have laboratory evidence of infection.
The DCHD interviewed all 13 people reported ill. Predominant symptoms reported were fever and chest tightness. Other symptoms included malaise, myalgia, night sweats, weight loss, headache, and bodyaches. The median incubation period of illness was 7-10 days. All 13 people sought medical attention, and one person was hospitalized for several days. Six cases submitted specimens for laboratory analysis, including serum, urine, and tissue from a lung biopsy.
According to a representative of the DCHD, members of the mission group dug trenches for homes on three consecutive days. Thirteen of the 16 mission members who were exposed to soil and debris while digging became symptomatic. The exposure time varied with assigned work schedules. One case spent an extensive amount of time in the trenches, thus prolonging exposure.
Six cases submitted serum, urine, or lung tissue to the local hospital laboratory for analysis. All six cases tested positive for histoplasmosis
This investigation confirms that an outbreak of histoplasmosis occurred among church mission members performing excavation activities from June 14-24, 2007. The extremely short window of illness onset and lack of subsequent cases after the outbreak strongly suggest a common source exposure. The only common exposure among all the cases was the manual digging of trenches for new home construction in Nicaragua.
The causative agent of this outbreak was Histoplasma capsulatum. Six people tested positive. The clinical symptoms described (headache, fever, malaise, myalgia, weight loss, and fever) are consistent with histoplasmosis. The median incubation time was 7-10 days, which falls within the incubation period for histoplasmosis. Infection generally occurs when H. capsulatum spores are inhaled. Most infections are asymptomatic or mild, although severe illness may occur in people with weakened immune systems or those who are exposed to high levels of fungal spores. The infection is not transmitted person to person.
H.capsulatum is normally found in soils with a high nitrogen content, including soil throughout Indiana and other states within the Ohio Valley. Soils enriched with bird or bat droppings usually have high nitrogen levels that facilitate fungal growth. Fungal spores in soil may become airborne if soil is disturbed, such as during construction, excavation, or earthquakes, creating opportunity for infection. The one common exposure in all cases was the excavation of trenches for new home construction in Nicaragua. Soil disturbance from trench excavation most likely created aerosols of fungal spores that were inhaled to cause infection.
Most instances of histoplasmosis can be prevented by observing the following guidelines: