Escherichia coli O157:H7 Cluster Associated With Deer Harvested at a Single Wildlife Hunting Area,Oregon,2017

Abstract

The Oregon Health Authority routinely investigates clusters of reportable enteric diseases identified by whole-genome sequencing. While investigating 2 cases of Escherichia coli O157:H7 in 2019, in which both patients were exposed to the same home-processed “jerky” and clinical isolates matched within 2 single nucleotide polymorphisms (SNPs), we discovered, by searching the National Library of Medicine’s National Center for Biotechnology Information website, 3 other cases of E coli O157:H7 from 3 Oregon counties—Tillamook, Umatilla, and Douglas—whose clinical isolates were within 9 SNPs of the 2 initial matched cases. We analyzed interview data for 3 case patients and followed up with additional hypothesis-generating questions. Onset of illness for the Tillamook, Umatilla, and Douglas county cases were October 7, 2017, October 27, 2017, and April 30, 2018, respectively. The median age of the 5 case patients was 16 years. Parents of 2 of the 5 case patients, each from a different county, had harvested deer approximately 20 miles from each other in the same Douglas County wildlife hunting unit in late September 2017. The case from Umatilla County was lost to follow-up. Although it is well documented that deer are a viable and substantial reservoir of E coli O157:H7, to our knowledge, this is the first time that venison from a common wildlife hunting unit was found to be associated with a cluster of illnesses. This finding suggests a geographic nidus for E coli O157:H7. We recommend routinely asking about wildlife hunting units when developing exposure hypotheses involving potential venison-associated clusters.

The Oregon Health Authority (OHA), in conjunction with local health jurisdictions, routinely investigates clusters of cases of reportable diseases, many of which are enteric diseases, identified by whole-genome sequencing (WGS). It uses several tools for data analysis, including the National Library of Medicine’s National Center for Biotechnology Information (NCBI) website, which houses WGS data from clinical and environmental isolates. ¹ On July 9, 2019, the Oregon State Public Health Laboratory identified 2 clinical isolates (ie, obtained from the stool samples of case patients; PNUSAE026657 and PNUSAE026809) of Escherichia coli O157:H7 (E coli O157:H7), which were related within 2 single nucleotide polymorphisms (SNPs), by using WGS; both isolates were from residents of Yamhill County, Oregon. OHA epidemiologists discovered 3 other clinical isolates (PNUSAE010570, PNUSAE010832, and PNUSAE014145) from residents of 3 other Oregon counties (Douglas, Tillamook, and Umatilla) via the NCBI website; the isolates were related within 9 SNPs of the initial Yamhill County isolates. OHA epidemiologists investigated to identify a common source.

Methods

OHA and Douglas County epidemiologists attempted to administer structured, hypothesis-generating interviews of the 5 case patients to ascertain exposure histories. State-assigned interviewers conducted the interviews, which took place in November 2017 (Tillamook County case patient), May 2018 (Douglas County case patient), and July 2019 (Yamhill County case patient). The Umatilla County case patient was lost to follow-up. The Institute of Environmental Health Laboratories (in Shoreline, Washington) performed molecular analyses of isolates from venison obtained from the Douglas County case patient in July 2019 and Tillamook County case patient in October 2019; the case patient from Umatilla County was lost to follow-up. Because isolates from a deer–strawberry-associated E coli O157:H7 outbreak in Oregon in 2011 were available, we compared the 5 Oregon clinical isolates with the environmental and clinical isolates from that 2011 outbreak. ²

Results

Illness onset of the 5 case patients (4 females, 1 male) ranged from October 7, 2017, to July 3, 2019. The median age was 16 years; all case patients were aged <18 years; the median duration of illness was 7.5 (range, 6-11) days; no case patients were hospitalized. We completed initial interviews with all but 1 case patient (from Umatilla County). Hypothesis-generating interviews were completed with 3 case patients: 1 from Douglas County, 1 from Tillamook County, and 1 from Yamhill County. Parents of the case patients from Douglas and Tillamook counties had harvested deer approximately 20 miles from each other in late September 2017 from the same Douglas County wildlife hunting unit—the Melrose Unit—which encompasses 960 square miles. The Douglas County case patient, whose disease onset occurred in late April 2018, consumed venison that had been stored in the family’s freezer from October 2017, when the deer was harvested.

The 2 case patients from Yamhill County with illness onset on July 3, 2019, had eaten the same home-processed jerky, which we learned about from the initial interviews, but both case patients declined to reveal its source or the type of meat (ie, deer, beef, elk, or other). Yamhill County Environmental Health did eventually obtain the name of the person who made the jerky (a mutual acquaintance), but he did not cooperate with the investigation, and, thus, we were unable to obtain a sample of the jerky or samples from the equipment used to make the jerky. This person had purchased deer-hunting tags in 2017 but did not claim them (personal communication, Colin Gillin, DVM, Oregon Department of Fish and Wildlife, July 25, 2019); that is, he did not report to the Oregon Department of Fish and Wildlife in 2017 whether he had harvested a deer, which is required by law. The venison samples collected from the Tillamook and Douglas county case patients had negative test results for E coli O157:H7; WGS analyses revealed >100 allele differences between the 5 clinical isolates of this cluster and the E coli O157:H7 deer–strawberry-associated Oregon outbreak isolates of 2011.

Discussion

Two case patients from 2 counties in Oregon in this cluster of 5 Oregon residents, with illness onset about 6 months apart, were exposed to venison harvested 20 miles apart in the same wildlife hunting unit in fall 2017. That the venison had been stored in a freezer and consumed in April 2018 explains the 6-month difference in the dates of illness onset. The well-documented deer–strawberry-associated outbreak of E coli O157:H7 in Oregon in 2011 corroborated that deer are a viable and substantial reservoir of E coli O157:H7. ² Although no definitive proof exists that the 2 case patients who had consumed home-processed jerky consumed venison jerky, the dangers of E coli O157:H7 illnesses associated with home-processed jerky, including venison jerky, are also well known. ^3,4 This venison-associated outbreak appears to be the first time, however, that a cluster of this kind was associated with a wildlife hunting unit. Temporal and geographic differences between the 2011 deer–strawberry-associated E coli O157:H7 outbreak in Washington County, Oregon (>150 miles from Douglas County), might explain the >100-allele difference between the 2 distinct clusters. This finding suggests a geographic nidus for E coli O157:H7. We recommend routinely asking about the wildlife hunting units in which deer are harvested when developing exposure hypotheses for potential venison-associated clusters.