Hyperendemic urban blastomycosis.

Within the United States, blastomycosis is primarily endemic in the Mississippi and Ohio River valleys, but reliable figures as to its prevalence and incidence are scarce. A review of pathology department files and medical records from three hospitals in Rockford, Illinois, revealed 32 documented cases of blastomycosis in an eight and one-half year period beginning in March 1981. Twenty-three of these cases were urban since they occurred within the Rockford census tract boundaries--an incidence more than 3.5 times greater than expected in an endemic area. Addresses of patients in 18 of the 23 cases were concentrated at the northeast and southwest ends of the city. Implications are discussed.