Non-Rural Point Source Blastomycosis Outbreak Near a Yard Waste Collection Site

Abstract

Background: Blastomycosis is a potentially fatal infection caused by the fungus Blastomyces dermatitidis.During January 1 through March 5, 2006, twenty-one laboratory confirmed cases of blastomycosis were reported among residents of an endemic area in north-central Wisconsin; a striking increase compared with previous years. The objective of the study was to determine if an observed increase in blastomycosis among residents of an urban area in north-central Wisconsin was caused by a pointsource exposure and to identify its source. Methods:We compared epidemiologic features, and signs and symptoms of B. dermatitidis infection among 46 historic (1999)(2000)(2001)(2002)(2003)(2004)(2005) and 21 possible outbreak case patients. In addition, a case-control study was conducted to compare risk factors of the outbreak case patients with those of 64 age, gender, and geographically-matched control subjects. We conducted site inspections, evaluated meteorological data, genetically compared outbreak and non-outbreak isolates, and attempted environmental detection of B. dermatitidis using polymerase chain reaction, in vitro isolation, and in vivo isolation by tail vein injection of mice. Results:The unusual risk profile of this outbreak included: residence within non-rural city limits with limited time spent outdoors and an equivalent gender ratio and young median age among case patients consistent with common source rather than unrelated exposures. Thirteen of fourteen outbreakassociated clinical isolates of B. dermatitidis clustered in the same genetic group by PCR-RFLP analysis. Inspections near the cluster center suggested a yard waste collection site as the probable exposure source. B. dermatitidis nucleic acid was detected in one of 19 environmental samples. Environmental and meteorological conditions and material management practices were identified that may have facilitated growth and dispersal of B. dermatitidis conidia near this residential area. Conclusions:Results of our investigation of this large non-rural outbreak of blastomycosis suggest bioaerosol hazards may exist near yard waste collection and composting facilities, especially where pine tree litter is present, in B. dermatitidis endemic areas.

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

“…Furthermore, like B. gilchristii (PS2), genotypic group A isolates showed an analogous geographic distribution and lacked genetic variation compared with other genotypes [33]. Interestingly, two separate outbreak investigations in Wisconsin have identified genotypic group A as the predominant organism isolated from patients [33], [71]. Similarly, B. gilchristii (PS2) was responsible for the majority of Wisconsin and northwestern Ontario cases in our analysis.…”

“…In these areas, incidence rates exceed 100 cases per 100 000 with documented outbreaks [28], [60], [68], [70], [71]. Genetic analysis of B. gilchristii (PS2) isolates demonstrated low levels of genetic diversity with only 7 unique sequence types encompassing 8 unique polymorphisms in 39 isolates.…”

Population Genetic Structure of Clinical and Environmental Isolates of Blastomyces dermatitidis, Based on 27 Polymorphic Microsatellite Markers

“…We did not test for associations between genetic group and nonhuman host species, due to the lack of statistical power to detect differences. Interestingly, isolates obtained from patients and the environment that were identified during documented outbreak investigations (16,17,32) all clustered within genetic group 1. Although the number of isolates in this category is small (n ϭ 18) (Table 1), it may indicate phenotypic differences between the two groups related to infectivity and/or virulence.…”

Blastomycosis in Minnesota, USA, 1999–2018

“…Case series and outbreak reports have provided insight into the ecology of Blastomyces spp. and possible risk factors for human infection (16)(17)(18)(19). Outbreaks have been associated with outdoor recreation (17,(20)(21)(22) and with construction, excavation, or local environmental sources such as yard waste compost (18).…”