Histoplasmosis 
Annual Summary of Reportable Diseases

Histoplasmosis is caused by the soil-dwelling dimorphic fungus Histoplasma capsulatum. Infection typically results from inhalation of aerosolized spores, and symptomatic infections usually involve pulmonary disease, though disseminated or nonpulmonary infections are possible. Common activities associated with illness include farming, exposure to soil enriched with bird or bat guano, remodeling or demolition of old buildings, and clearing trees or brush in which birds have roosted. In 2022, there were 45 confirmed and 149 probable cases of histoplasmosis reported. These numbers are consistent with the case counts from previous years, with the exception of 2020. There was one outbreak of histoplasmosis, from the demolition of a chimney in an old farmhouse in Sibley County, which affected three people. The chimney was filled with bat or bird guano, and the people involved were not wearing respiratory protection while working on the chimney. Two of the outbreak-associated cases died. The median age of histoplasmosis cases in 2022 was 55 years (range, 1 to 87 years), and 103 (53%) were male. Of the 175 cases for whom race was reported, 157 (90%) were white, 9 (5%) were Black, 4 (2%) were Asian, 3 (2%) were American Indian/Alaska Native, 1 (<1%) was Native Hawaiian/Pacific Islander and 1 (<1%) was more than one race. Of the 167 for whom ethnicity was reported, 8 (5%) were Hispanic. When hospitalization status was reported, 80 of 180 (44%) cases were hospitalized. Median hospitalization duration was 5 days (range, 1 to 72 days). There were 12 deaths, a case fatality rate of 6%. Histoplasmosis was listed as the primary cause of death for 4 of the 12 cases, while the others had other illness listed or the data were not available. From 2017 to 2022, 1,066 cases of histoplasmosis were reported. The annual incidence of histoplasmosis in Minnesota in 2022 was 3.3 cases per 100,000 population, similar to the annual incidence of 3.2 to 3.7 cases per 100,000 since 2017. The average annual incidence of histoplasmosis by county shows that cases occur more frequently in southern and western counties of Minnesota (Figure 1). This is in contrast to the other endemic fungal disease found in Minnesota, blastomycosis, which has higher incidence levels in northern and northeastern counties of Minnesota. While clinicians should test for both diseases when clinical illness is consistent with a fungal infection, these maps can help assess possible risks in different parts of the state.

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Histoplasmosis is caused by the soil-dwelling dimorphic fungus Histoplasma capsulatum. Infection typically results from inhalation of aerosolized spores, and symptomatic infections usually involve pulmonary disease, though disseminated or nonpulmonary infections are possible. Common activities associated with exposure include farming, exposure to soil enriched with bird or bat guano, remodeling or demolition of old buildings, and clearing trees or brush in which birds have roosted. In 2021, there were 38 confirmed and 152 probable cases of histoplasmosis reported. These numbers are consistent with the case counts from the years prior to the COVID-19 pandemic. The median age of cases was 48 years (range, 0 to 88 years), and 112 (59%) were male. Of the 133 cases for whom race was reported, 112 (84%) were white, 11 (8%) were Black, 6 (5%) were Asian, 2 (1.5%) were American Indian/Alaska Native, 1 (<1%) was Native Hawaiian/Pacific Islander and 1 (<1%) was more than one race. Of the 130 for whom ethnicity was reported, 4 (3%) were Hispanic. When hospitalization status was reported, 38 of 70 (54%) cases were hospitalized. Median hospitalization duration was 5 days (range, 1 to 47 days). There were 2 deaths among the 54 cases for which outcome was reported, a case fatality rate of 4%. Histoplasmosis was the primary cause of death for both of those cases. From 2017 to 2021, 872 cases of histoplasmosis were reported. The annual incidence of histoplasmosis in Minnesota in 2021 was 3.3 cases per 100,000 population, similar to the average annual incidence of 3.0 cases per 100,000 for 2017-2020. The average annual incidence of histoplasmosis by county shows that cases occur more frequently in southern and western counties (Figure 2). This is in contrast to the other endemic fungal disease found in Minnesota, blastomycosis, for which the highly endemic region includes the northern and northeastern counties of Minnesota. While clinicians should test for both diseases when clinical illness is consistent with a fungal infection, these maps may help assess possible risks in different parts of the state.

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In 2020, there were 54 confirmed and 47 probable cases of histoplasmosis reported. Surveillance for histoplasmosis was severely affected by response to the COVID-19 pandemic, and these numbers, which are lower than past years, likely reflect that. Additionally, MDH received laboratory reports for 74 cases which would have counted as probable cases, but we were unable to obtain the necessary clinical information. The median age of cases was 52 years (range, 1 to 92 years); 71 (70%) were male. Of the 87 cases with race reported, 75 (86%) were white, 6 (7%) were black, 3 (3%) were Asian, and 3 (3%) were Native Hawaiian/Pacific Islander. Of the 84 with ethnicity reported, 9 (11%) were Hispanic. Fiftyfour cases (53%) were hospitalized, for a median of 4.5 days (range, 1 to 27 days) and of the 34 whose status was known, 29 (85%) were immunocompromised. Of the 75 cases whose outcome was reported, 7 (9%) cases died, and histoplasmosis was the primary cause of death in 4 of those cases, while the cause of death was not reported for the other 3. Again, this case fatality rate is higher than previous years and likely results from underreporting of the outcome when patients survived. From 2017 to 2020, 682 cases of histoplasmosis were reported. The 2020 annual incidence of histoplasmosis in Minnesota was 1.8 cases per 100,000 population. However, the average annual incidence for 2017 – 2019 was 3.5 cases per 100,000 which is more likely reflective of the true disease burden. The average annual incidence of histoplasmosis by county shows that cases occur more frequently in southern and western counties (Figure 1). This contrasts to the other endemic fungal disease found in Minnesota, blastomycosis, whose highly endemic region includes the northern and northeastern counties of Minnesota. While clinicians should test for both diseases when clinical illness is consistent with a fungal infection, these maps may help assess possible risks in different parts of the state. Histoplasmosis is caused by the soildwelling dimorphic fungus Histoplasma capsulatum. Infection typically results from inhalation of aerosolized spores, and symptomatic infections usually involve pulmonary disease, though disseminated or non-pulmonary infections are possible. The Mississippi River Valley is known to be an endemic area. Additionally, geographic microfoci exist inside and outside endemic areas, and are usually associated with soil containing bird or bat guano. Common activities associated with 10 DCN 48;1 2022 exposure include farming, exposure to soil enriched with bird or bat guano, remodeling or demolition of old buildings, and clearing trees or brush in which birds have roosted.

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In 2019, there were 61 confirmed and 153 probable cases of histoplasmosis, an increase from 2017 and 2018. A new national case definition was implemented 2017; thus, comparisons to earlier years are difficult to make. The median age of cases was 52 years (range, 3 to 86 years); 133 (62%) were male. Of the 174 cases with race reported, 162 (93%) were white, 5 (3%) were black, 5 (3%) were Asian/ Pacific Islander, 1 (1%) was American Indian/Alaskan Native, and 1 (1%) reported more than one race. Of the 150 with ethnicity reported, 5 (3%) were Hispanic. One hundred one cases (49%) were hospitalized, for a median of 4 days (range, 1-28 days), and of the 166 whose status was known, 61 (37%) were immunocompromised. Ten (5%) cases died, and histoplasmosis was the primary cause of death in 8 of these cases.

From 2017 to 2019, 581 cases of histoplasmosis have been reported. The average annual incidence of histoplasmosis in Minnesota was 3.3 cases per 100,000 population.

Histoplasmosis is caused by the soil dwelling dimorphic fungus Histoplasma capsulatum. Infection typically results from inhalation of aerosolized spores, and symptomatic infections usually involve pulmonary disease, though disseminated or non-pulmonary infections are possible. The Mississippi River Valley is known to be an endemic area. Additionally, geographic microfoci exist inside and outside endemic areas, and are usually associated with soil containing bird or bat guano. Common activities associated with exposure include farming, exposure to soil enriched with bird or bat guano, remodeling or demolition of old buildings, and clearing trees or brush in which birds have roosted. A subset of cases from 2018 and 2019 were enrolled in an enhanced surveillance interview, including 50 confirmed cases and 47 probable cases. These cases were asked about possible exposures, including bird or bat droppings, construction, demolition, gardening or other handling of plants or trees. Eighty-two (85%) cases reported at least one of these. The most commonly reported exposure was gardening or other handling of plants or trees (51 cases, 53%), while 32 (33%) cases reported exposure to construction or demolition, and 24 (25%) cases reported exposure to either bird or bat guano.

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Histoplasmosis is caused by the soil-dwelling dimorphic fungus Histoplasma capsulatum. Infection typically results from inhalation of aerosolized spores, and symptomatic infections usually involve pulmonary disease, though disseminated or non-pulmonary infections are possible. The Mississippi River Valley is known to be an endemic area. Additionally, geographic micro-foci exist inside and outside endemic areas, and are usually associated with soil containing bird or bat guano. Common activities associated with exposure include farming, exposure to soil enriched with bird or bat guano, remodeling or demolition of old buildings, and clearing trees or brush in which birds have roosted.

A new case definition was implemented in 2017; thus, the current case count can only be compared with that year. In 2018, there were 57 confirmed cases and 127 probable cases of histoplasmosis compared to 36 confirmed cases and 147 probable implemented in 2017; thus, the current case count can only be compared with that year. In 2018, there were 57 confirmed cases and 127 probable cases of histoplasmosis compared to 36 confirmed cases and 147 probable cases in 2017. The median age of cases was 46.5 years (range, 4 months to 84 years); 118 (64%) were male. Of the 157 cases with race reported, 137 (87%) were white, 7 (5%) were black, 6 (4%) were Asian/ Pacific Islander, 4 (3%) were American Indian/Alaska Native, and 3 (2%) reported more than one race. Of the 138 with ethnicity reported, 7 (5%) were Hispanic.

Seventy-two cases (39%) were hospitalized, and of the 152 whose status was known, 37 (39%) were immunocompromised. Three (2%) cases died, and histoplasmosis was the primary cause of death in 1 of those cases.

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• Archive of Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health
  Archive of past summaries (years prior to 2023 are available as PDFs).