Cattle Are Likely Source of Recent Outbreaks of E. Coli Associated With Leafy Greens

A fall 2020 outbreak of Shiga toxin-producing Escherichia coli (STEC) O157:H7 linked to leafy greens grown in California in close proximity to cattle was detailed in an investigation report recently released by the US Food and Drug Administration.

The report follows preliminary findings released in January that indicated the outbreak strain was found in cattle feces about 1.3 miles upslope from a produce farm tied to outbreaks.

“This finding drew our attention once again to the role that cattle grazing on agricultural lands near leafy greens fields could have on increasing the risk of produce contamination, where contamination could be spread by water, wind or other means,” a statement from Frank Yiannas, the FDA’s deputy commissioner for food policy and response, said. “In fact, the findings of foodborne illness outbreak investigations since 2013 suggest that a likely contributing factor for contamination of leafy greens has been the proximity of cattle.”

The 2020 outbreak is the latest in a series of E. coli outbreaks linked to leafy greens in the California central coast growing region that have occurred each fall since 2017 and have included recurring strains, recurring region and recurring issues with activities on adjacent land. It caused 40 reported illnesses between August and December 2020.

The FDA issued recommendations for farmers in the region, which encompasses Salinas Valley and Santa Maria. They include participation in the California Longitudinal Study and the California Agricultural Neighbors workgroup, along with root cause analyses and implementation of prevention and verification measures.

“(W)e recommend that all growers be aware of and consider adjacent land use practices, especially as it relates to the presence of livestock, and the interface between farmland, rangeland and other agricultural areas, and conduct appropriate risk assessments and implement risk mitigation strategies, where appropriate,” Yiannas said in the statement.

The FDA report encourages collaboration among various groups, including livestock owners, leafy greens growers, state and federal government agencies and academia to address the issue.

The FDA also updated its Leafy Green Action Plan, issued in March 2020, noting progress made in advancing the safety of leafy greens and additional steps for further improvements.

Accomplishments completed during the past year include:

A new standardized protocol developed in collaboration with the US Environmental Protection Agency to evaluate the effectiveness of treatments in reducing microbial contamination in agricultural water.

An investigation report of three fall 2019 outbreaks linked to contamination of romaine lettuce outlining epidemiological and on-farm investigation approaches.

A proposed rule to establish additional traceability recordkeeping requirements for those who manufacture, process, pack and hold designated foods.

A traceability pilot final report in an effort to design and initiate a pilot on concepts such as testing interoperability of tracing systems and public-private data sharing.

A retrospective analysis of outbreaks associated with leafy greens.

New steps for 2021 include convening public meetings, distributing online tools, developing an agriculture water systems workshop to improve agriculture water safety; conducting additional focused sampling; developing fact sheets to increase awareness and address concerns about adjacent lands; participating in a colloquium planned for early 2021; developing machine learning tools to support risk mitigation efforts; and more.

Officials reported the first STEC outbreaks linked to leafy greens in 1995. Between 2009 and 2018, the FDA and US Centers for Disease Control and Prevention identified 40 foodborne outbreaks of STEC associated with leafy greens.

An outbreak in 2019 linked to romaine lettuce grown in California’s central coast region sickened 23 people, including 11 who were hospitalized. In 2017, outbreaks in North America sickened 17 people in 13 US states and 41 people in 5 Canadian provinces.

STEC infections can sometimes lead to severe diarrhea and kidney damage.