Investigation of potential reservoirs of shiga toxin-producing E. coli and Salmonella in produce production areas of Arizona and Mexico. (rapid response)

In May 2010, Romaine lettuce grown in Arizona was implicated as the vehicle in a multi-state outbreak of E. coli O145 infections. This is the first known leafy green-related shiga toxin producing Escherichia coli (STEC) outbreak traced to the Yuma production region. Pre-harvest contamination was suspected, but the source of the outbreak was not definitively determined. The long-term goal of this project is to identify potential domestic and wild animal reservoirs of foodborne pathogens in produce production regions of Arizona and Northern Mexico. In the first “emergency response” phase of the project we are determining if free-roaming domestic dogs and coyotes in these regions shed STEC and/or Salmonella enterica in their feces. We focused on canids based on feedback from growers who reported that unleashed, free-roaming domestic dogs and coyotes are common in this region. Intrusions into produce fields have resulted in damage to leafy greens and other crops, but the food safety risk from stray dogs and coyotes is unclear. To address this gap in knowledge, we conducted a study during the 2010- 2011 southwestern desert growing season to assess foodborne pathogen carriage in stray dogs and coyotes. In a unique industry-university partnership, the produce company managed the field activities including specimen collection and shipping, while UC Davis investigators conducted laboratory and data analyses. Three animal shelters were enrolled in the study and visited monthly to sample fresh feces from dogs recently impounded. Fresh coyote scat was collected at dawn by walking the dirt roads near produce fields. Samples were shipped from Yuma to Davis overnight and processed within 24 hours. Standard culture methods were used to isolate STEC and Salmonella. No shiga toxin-producing E. coli was identified among 473 samples, although 8 E. coli isolates belonging to serogroups O26, O145, or O157 were positive for other virulence determinants by PCR (eae, hylA) suggesting the potential to be a human pathogen. Overall, Salmonella was cultured from 33 (9.2%) of 358 dog fecal samples compared with 33 (32%) of 103 coyote scat samples. Twenty-nine Salmonella serotypes were identified including types that have been associated previously with human illness.

The long-term goal of this project is to identify potential domestic and wild animal reservoirs of foodborne pathogens in leafy green production regions of Arizona and Mexico. The first phase of the proposed study will determine if free-roaming domestic and wild canids (e.g., coyotes) in these geographic regions shed E. coli O157:H7, and/or Salmonella in their feces.

See the final report PDF to view the appendix referenced below. 

- Continue to follow GAP metrics as described in the Arizona and California Leafy Green Market Agreements, especially those relating to animal intrusions and pre- and postharvest environmental assessments 

- Continue to follow the Guidance for Industry: Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables relating to wildlife and animal intrusions 

- Conduct a follow-up survey to determine Salmonella and STEC prevalence in other potential domestic and wildlife reservoirs in desert produce production regions 

- Because of the high percent positive in coyote scat samples, subsequent surveys should attempt to determine the Salmonella concentration using a quantitative assay

- Compare domestic and wildlife Salmonella and STEC subtypes with strains from other environmental samples in the region (canals, irrigation water, soil amendments) 

- Disseminate an English and Spanish language Fact Sheet on salmonellosis to animal shelters to prevent transmission among shelter animals and people (Appendix A)