An Outbreak of Human and Canine Blastomycosis

In the summer and fall of 1988, three humans and one dog in a lakeshore community in northern Wisconsin were found to have blastomycosis on the basis of the results of cultures and histologic studies; the infection was also suspected in one human and four dogs on the basis of clinical data. Serologic testing with use of enzyme immunoassay for antibody to the A antigen of Blastomyces dermatitidis was performed for 77 additional human residents and visitors in the area an average of 9 months after the outbreak. Titers of antibody of greater than or equal to 1:32 were considered presumptive evidence of blastomycosis, and measurement of such titers enabled identification of 18 additional suspected cases in this group, compared with none in a control group (n = 40). Of the 22 humans with confirmed and suspected cases, 16 (73%) were asymptomatic. Epidemiologic and meteorologic data gathered during this period suggested an associated between this outbreak and the presence of dust from excavation for a hotel across the lake. The result of this study further confirm the common occurrence of self-limited and subclinical infection with B. dermatitidis and suggest that excavation in an area endemic for B. dermatitidis is a risk factor for human and canine infection.