A person becomes infected after inhalation of fungal spores. A group of people may be exposed by the same release of spores.
Reasons why an epidemic of blastomycosis may go unrecognized:
(1) low-grade, self-limited infection in immunocompetent individuals
(2) lack of systemic spread
(3) group of visitors from different areas who return home
(4) going to different hospitals
(5) failure to perform diagnostic testing
(6) patients present as isolated cases over a period of time
Reasons why an epidemic is more likely to be recognized:
(1) group of people in communication with each other
(2) recognition of a large number of blastomycosis in dogs or other animals
(3) single physician or medical group
(4) surge in cases reported to a central data site
