Epidemiology, Spatial Distribution, and Treatment Patterns of Blastomycosis in the United States
Open AccessBlastomyces dermatitidis and Blastomyces gilchristii, dimorphic fungi, are capable of causing blastomycosis infection among humans, dogs, and other mammals. Severity of infection from either fungal species in humans can vary greatly from asymptomatic to severe pulmonary or disseminated disease. The epidemiology is poorly understood as reliable and rapid diagnostic assays do not exist. Blastomyces is difficult to culture from the environment and disease reporting is currently only mandatory in Arkansas, Louisiana, Michigan, Minnesota, Mississippi, and Wisconsin. This study seeks to provide a comprehensive and updated epidemiologic description of blastomycosis in the United States, which will greatly add to the current literature. Specifically, we use the Agency for Healthcare Research and Quality State Inpatient Database, a large, publically available state hospitalization dataset and Wisconsin surveillance data. We describe the epidemiology of blastomycosis throughout the United States by reporting state-specific hospitalization incidence and information on demographic factors. We identify spatial clusters of disease in the endemic area using ArcGIS and the Getis-Ord Gi* spatial analysis statistic. We identify environmental factors associated with the clusters that we identify in the endemic area. Finally, we describe treatment patterns of hospitalized cases in Wisconsin, a state where blastomycosis is endemic. State-specific blastomycosis-associated hospitalization incidence was highest in the states within the Mississippi and Ohio River valleys. The highest hospitalization incidence was in Wisconsin, with a state-specific hospitalization incidence of 2.9/ 100,000. Among the five states with the highest hospitalization incidence, blastomycosis-associated hospitalizations increased significantly in Illinois and Kentucky and these trends varied by state. We identified a higher incidence of hospitalization among males and a median age of 53 years. Using the Getis-Ord Gi* statistic, we identified six clusters of higher blastomycosis-associated hospitalization incidence within the blastomycosis endemic area. We identified maximum temperature, percentage of persons aged ≥ 65 years and mercury and copper soil content as being associated with these six clusters. Finally, we found that nearly half of all cases in the Wisconsin surveillance system had at least one hospitalization for blastomycosis and 12% of cases had multiple blastomycosis hospitalizations. The median length of stay for these blastomycosis-associated hospitalizations was 7 days (range 1 to 43 days). Public health region in Wisconsin and month of disease onset were identified as risk factors for cases having at least one hospitalization. Sex was identified as a risk factor for having multiple hospitalizations as males had almost three times the odds of having multiple hospitalizations as compared to females (OR: 2.9; 95% CI 1.2, 6.6). Using a large, population-based dataset and state surveillance data, this study provides an updated and comprehensive epidemiologic description of blastomycosis in the United States. The study highlights specific areas where clinicians should have increased awareness of the disease which could decrease delays to diagnosis.
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