February 27, 2024

Recurring E. coli O157:H7 Strain Linked to Leafy Greens Outbreaks

A recurring E. coli O157:H7 strain linked to leafy greens outbreaks has been identified, according to the Centers for Disease Control and Prevention (CDC). The report was issued in the CDC’s Dispatch for September 2023.

Recurring E. coli O157:H7 Strain Linked to Leafy Greens Outbreaks

Researchers found that this strain emerged in late 2015. The strain is emerging, reoccurring, or persistent (REP strain) and has caused illness over an extended time period.

E. coli O157H7 causes about 63,000 domestically acquired foodborne illnesses in the United States every year, and causes 20 deaths. This illness causes symptoms including severe abdominal cramps and bloody diarrhea. A complication of this infection, called hemolytic uremic syndrome, can develop in children under the age of five, which is a ty-pe of kidney failure.

Healthy cattle are the main reservoir for the pathogen, which lives in their guts. Contact with animals, eating contaminated food, drinking contaminated water, and contact with environmental sources have been the typical sources of outbreaks.

But contaminated leafy greens have recently been recognized as a major source of E. coli O157:H7 illnesses and outboards. In attribution estimates for 2020 based on outbreak data, about 58.1$ of E. coli illnesses were attributed to vegetable row crops, which  include leafy greens. During the time period of 2009 to 2018, 32 confirmed or suspected outbreaks of E. coli O157:H7 linked to contaminated leafy greens occurred in the U.S. and Canada.

A large E. coli outbreak in late 2019 that sickened 167 people in 27 states and hospitalized 85 patients is the focus of the study. It was associated with romaine lettuce harvested from the Salinas Valley area of California.

The strain consists of two clades (a grouping with a common ancestor) with different geographic distributions. REP strains like this one are distinct from discrete outbreak pathogens where many people are sickened in a short time frame. The authors say that detailed genomic characterization of more REP strains will be needed to find factors that contribute to their emergence and persistence in the environment.

Citation: Chen JC, Patel K, Smith PA, Vidyaprakash E, Snyder C, Tagg KA, et al. Reoccurring Escherichia coli O157:H7 strain linked to leafy greens–associated outbreaks, 2016–2019. Emerg Infect Dis. 2023 Sep [date cited]. https://doi.org/10.3201/eid2909.230069

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