Epidemiology of human blastomycosis in Vilas County, Wisconsin. II: 1991-1996.

PURPOSE: A previous report identified Vilas County, Wisconsin, as an area highly endemic for blastomycosis based on a case series 1979-90. This study was done to compare the epidemiologic features of persons with this disease over the following six years.

METHODS

Compilation of data from the 47 mandatory physician/laboratory case reports of blastomycosis, disease onset 1991-96, received at the Vilas County Health Department; case mapping by site visit; and statistical comparison to the previous series.

RESULTS

The estimated mean annual incidence rate for Vilas County during 1991-96, 40/100,000, remains unchanged from 1984-90. Cases were again disproportionately represented in the southeast corner of the county, and 36/46 lived within 1/4 mile of water. There was a trend toward a higher proportion of female cases in this study (27/47) compared to the prior report (28/73; P = 0.06); the mean age, 47 years, did not differ. Among 32 patients whose activities were recorded, a minority engaged in hunting (4), fishing (4) and gardening (12) prior to disease onset; but 19/32 recalled excavation prior to exposure compared to 17/60 in 1979-90 (P < 0.01). Among cases with a pulmonary presentation, winter onset cases (3/40) were significantly fewer than in 1979-90 (19/55). However, over the entire 18 years there was no disproportionately represented season.

CONCLUSIONS

In highly endemic Vilas County, the mean annual incidence of human blastomycosis appears stable over the past 13 years. A combined case series of 18 years reveals no predilection by gender or season of onset.