Blastomyces dermatitidis, fungal ecology, mycoses, weather
Blastomycosis is a serious fungal infection contracted by inhalation of Blastomyces spores from the environment. Case occurrence in dogs in Vilas County, Wisconsin, has been associated with antecedent weather. We aimed to explore the effects of weather on the occurrence of human pulmonary blastomycosis in this area, and update exposure factors and symptoms since last published reports.
Mandatory case reports were reviewed. Chi-square test was used for categorical data of exposures, comparing 1979–1996 (n=101) versus 1997–June 2013 (n=95). Linear regression was used to model local weather data (available 1990–2013; n=126); Southern Oscillation Index (SOI), North Atlantic Oscillation Index (NAOI), and Wisconsin River water discharge (WRD) from the adjacent county (all available for 1984–2013; n=174); and case counts of known onset by warm (April–September) and cold (October–March) 6-month periods.
Distribution of pulmonary blastomycosis cases did not vary by season. Environmental exposures for the 1997–June 2013 group (mean age 45, 59% male) were: residence(76%), excavation (42%) and gardening (31%), all similar to the 1979–1996 group. Fishing (23% vs. 37%; P=0.09) and hunting (15% vs. 26%; P=0.13) exposures were less common in 1997–June 2013, but not significantly different. Overall, 69% of cases recalled some prior soil-disturbing activities. Considering the 6-month warm/cold periods, 19% of variation is explained by a direct relationship with total precipitation from two periods prior (P=0.005). There was no association of case occurrence with SOI, NAOI or WRD. Estimated annual incidence of blastomycosis for 1997–June 2013 was 27/100,000 compared with 44/100,000 for 1984–1996. Several symptoms were significantly less frequent in 2002–June 2013 compared to earlier years.
As with dogs, human pulmonary blastomycosis occurrence is partially determined by antecedent precipitation. It is unclear if recent lower incidence rates are due to less opportunity for exposure to weather, reduced fungal virulence or random variation.
Baumgardner DJ, Bernhard KA, Egan G. Pulmonary blastomycosis in Vilas County, Wisconsin: weather, exposures and symptoms. J Patient Cent Res Rev. 2015;2:25-33. doi: 10.17294/2330-0698.1050