August 06, 2013
1 min read

E. coli outbreak linked to strawberries contaminated by deer feces

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An outbreak of Escherichia coli O157:H7 in Oregon was traced back to a single farm where strawberries were contaminated by deer feces, researchers with the Oregon Health Authority reported in Clinical Infectious Diseases.

In August 2011, there was an increase in reported Shiga-toxigenic E. coli (STEC) and E. coli O157:H7 infections in northwestern Oregon. Investigators with the Oregon Public Health Division interviewed the reported cases to identify potential sources of the infections, and took environmental samples from the suspected location to conduct microbiology testing.

The outbreak had 15 cases. Results from questionnaires indicated that most of the cases had consumed strawberries and/or shopped at roadside stands or farmers’ markets. In a case control study that included 12 cases and 36 controls, illness was significantly associated with consuming strawberries from a roadside stand or farmers’ market.

Further investigation revealed that 14 of the cases consumed strawberries that were supplied by one particular farm. Among 111 specimens taken from fields at the farm, 10 samples (9%) were positive for E. coli O157:H7 and 13 (11.7%) were positive for STEC. Among the 50 samples that contained visible deer feces, 10 (20%) were positive for E. coli O157:H7, and all isolates were indistinguishable from the isolates of the cases. The isolates had a novel pulsed-field gel electrophoresis (PFGE) pattern combination compared with those in the PulseNet national database.

“This outbreak highlights problems concerning fecal contamination of produce from wildlife and the safety and regulatory oversight of agricultural production,” the researchers wrote. “Farming and processing practices are the most important barriers to contamination, because even the use of sanitizing solutions or vigorous washing — which is relatively infeasible with strawberries or other berries — is unlikely to eliminate bacterial surface contamination.”

Disclosure: The researchers report no relevant financial disclosures.