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Comparative Study
. 2011 Jun;9(2):57-65.
doi: 10.3121/cmr.2010.958. Epub 2010 Oct 25.

Non-rural point source blastomycosis outbreak near a yard waste collection site

John R Pfister  1 , John R Archer, Shelly Hersil, Tammi Boers, Kurt D Reed, Jennifer K Meece, Jennifer L Anderson, Joshua W Burgess, Thomas D Sullivan, Bruce S Klein, L Joseph Wheat, Jeffrey P Davis
Affiliations
Comparative Study

Non-rural point source blastomycosis outbreak near a yard waste collection site

John R Pfister et al. Clin Med Res. 2011 Jun.

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 point-source exposure and to identify its source.

Methods: We compared epidemiologic features, and signs and symptoms of B. dermatitidis infection among 46 historic (1999-2005) 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 outbreak-associated 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.

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Figures

Figure 1.
Figure 1.
Map of the 54452 zip code area demonstrating the location of blastomycosis cases (red circles) and controls (blue triangles) in relationship to the Prairie River. The municipal waste site cannot be resolved at this scale but is located near the densely clustered red circles in the center of the map.
Figure 2.
Figure 2.
Cumulative weekly precipitation departures from normal (in inches) during 2005, showing weeks with below (formula image) and above (formula image) normal precipitation. A moderate to severe drought resulted from precipitation levels 8.3 inches below normal during the period from March through mid-September 2005. This period of diminished precipitation was followed by a period of above-normal to normal precipitation during which time the pine needle pile was moved on November 21, 2005 (formula image) and subsequently followed by the estimated exposure period for the 21 blastomycosis outbreak case patients (formula image).
Figure 3.
Figure 3.
Outbreak and non-outbreak associated isolates of Blastomyces dermatitidis are shown grouped into 4 genetic types. Isolates obtained from case patients during the 2006 outbreak of blastomycosis in the 54452 zip code tabulation area in north-central Wisconsin are underlined; 13 of these 14 epidemiologically-linked isolates clustered in RFLP Group A.
See this image and copyright information in PMC

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