A case-control study of sporadic canine blastomycosis in Tennessee, USA

This study investigated environmental and host risk factors of canine blastomycosis in Knox County, Tennessee, USA. Data on 78 cases and 146 randomly selected controls were extracted from the medical database at the University of Tennessee Veterinary Teaching Hospital for the period 1977-1999. Home addresses of cases and controls were geocoded and linked to environmental risk factor data using a Geographic Information System (GIS) software. Multiple logistic regression analysis was performed to identify environmental and host factors associated with risk of canine blastomycosis. Important risk factors in the study area were sex, breed, age, and proximity to water whereas, soil type, pH, and organic matter content had no significant associations with blastomycosis risk in this study area. Males were 2.7 times (OR =2.7; 95% CI =1.3, 5.3) more likely to have blastomycosis than females. Blastomycosis risk was also higher in working (OR =4.6; 95% CI =1.5, 14.0) and sporting dogs (OR =6.2; 95% CI =2.4, 16.0) than other breeds. Disease risk was highest in 2-4-year-old dogs (OR =11.6; 95% CI =4.6, 29.1) and increased among dogs living near water bodies. Blastomycosis control strategies need to be designed with knowledge of the important risk factors in effect at the geographic location of interest.