Seasonal variations in the clinical presentation of pulmonary and extrapulmonary blastomycosis

Abstract

Blastomycosis is a granulomatous infection caused by the thermally dimorphic fungus, Blastomyces dermatitidis, for which seasonal variation has been proposed. We conducted a retrospective review of medical records of 324 patients with blastomycosis in Manitoba and northwestern Ontario. The average age of patients at the time of diagnosis was 39+/-20 (range, 0-85) years. Symptoms referable to blastomycosis were first noted in the autumn and winter (September to February) by 63% of the patients. The seasonal distribution of cases was different for localized pulmonary infection than the disseminated disease (P<0.0001). For localized lung disease, the peak incidence of symptom onset occurred in the autumn, and lowest incidence in the spring; one half (50%) of the patients with diffuse lung disease had onset of symptoms in the spring months and a few (11%) cases occurred during the summer. We noted a distinct seasonal variation in the clinical presentation of blastomycosis. The observed pattern suggests that summer environmental exposure and acquisition of the infection results in an early (1-6 months) localized pneumonia in the majority of cases, followed by later (4-9 months) reactivation or slow progression of asymptomatic infection resulting in isolated extrapulmonary or disseminated hematogenous disease in the minority.

Blastomycosis in Northwestern Ontario, 2004 to 2014

“…Consistent with other reports ( 1 , 3 , 6 ), 60% of patients were diagnosed between October and March. It has been suggested that the increase in patients diagnosed during the fall and winter months is due to acquisition of Blastomyces species conidia during the summer months, followed by a one to six month presymptomatic incubation period ( 6 ).…”

Phylogenetic Analysis Reveals a Cryptic Species Blastomyces gilchristii, sp. nov. within the Human Pathogenic Fungus Blastomyces dermatitidis

“…Standardized passage and storage history will be required to examine these correlations, as attenuated virulence among Blastomyces isolates has been documented [64]. Furthermore, these studies may succeed at revealing a genetic basis for variation in clinical symptoms and disease outcome observed for blastomycosis [24], [65], [66].…”

Incidence and Trends of Blastomycosis-Associated Hospitalizations in the United States

“…Effect modification between state and year was observed, indicating different temporal patterns for these states. This observation suggests that different factors may affect either blastomycosis infections [34], [35], hospitalizations or both in different geographic areas. Possible reasons for this increase may include increasing awareness, changing environmental factors, or an increase in disease incidence.…”