The Differential Diagnosis of Pulmonary Blastomycosis Using Case Vignettes: A Wisconsin Network for Health Research (WiNHR) Study

Pulmonary blastomycosis is an uncommon but serious fungal infection endemic in Wisconsin. Clinician awareness of the protean presentations of this disease may reduce diagnostic delay. This study addressed the diagnostic accuracy of physicians responding to case vignettes of pulmonary blastomycosis and the primary care differential diagnosis of this disease.Eight pulmonary blastomycosis cases were developed from case files. From these, 2 vignettes were randomly selected and mailed to primary care physicians in the Wisconsin Network for Health Research. Respondents were asked to list the 3 most likely diagnoses for each case.Respondents listed Blastomycosis as the most likely diagnosis for 37/227 (16%) case vignettes, and 1 of the 3 most likely diagnoses for 43/227 (19%). When vignettes included patient activity in counties with an annual incidence rate of blastomycosis greater than 2/100,000, compared to counties with lower incidence rates, diagnosis was more accurate (28/61 [46%] vs 15/166 [9%]; P0.001). Physicians with practice locations in counties with annual blastomycosis incidence rates2/100,000 listed blastomycosis more commonly than physicians from other counties (16/36 [44%] vs 27/177 [15%]; P0.001). This difference in accurate diagnosis remained significant in a multivariate model of practice demographics. Based on responses to the vignettes, pneumonia, cancer, non-infectious pulmonary disease, and tuberculosis emerged as the most-frequently noted diagnosis in the differential diagnosis of blastomycosis.Blastomycosis was not listed as 1of 3 primary diagnoses in a majority of cases when Wisconsin primary care physicians considered case vignettes of actual pulmonary blastomycosis cases. Diagnosis was more accurate if the patient vignette listed exposure to a higher incidence county, or if the physician practiced in a higher incidence county. In Wisconsin, failure to include blastomycosis in the differential diagnoses of illnesses associated with a wide variety of pulmonary symptoms suspected to represent infectious or non-infectious pulmonary, cardiac, or neoplastic disease, regardless of geographic exposure, could result in excess morbidity or mortality.