CDC: Reoccurring Strain of E coli is Source of Foodborne Illness


The Escherichia coli O157:H7 strain is linked to leafy greens–associated outbreaks over a multi-year period.

The CDC has identified a specific E coli strain, O157:H, to be responsible for numerous leafy greens–associated outbreaks during 2016-2019, according to a new study.

This study was published in the latest issue of CDC’s Emerging Infectious Diseases.

The investigators queried the PulseNet database, and used a subset of 245 isolates for further genomic analysis.

“A specific strain of E coli O157:H7 associated with leafy greens has been the source of ongoing enteric illness since late 2016. This strain is estimated to have emerged in late 2015 and consists of 2 clades with different geographic distributions, 1 of which has notable genomic features,” the investigators wrote.

The investigators point out that cattle are typically the largest reservoir for this strain of E coli, but in recent years, contaminated leafy greens have been recognized as a major source of outbreaks. “In foodborne illness attribution estimates for 2020 based on outbreak data, 58.1% of E coli O157:H7 illnesses were attributed to vegetable row crops, a category that includes leafy greens,” the investigators wrote.

Overall it is estimated that E coli O157:H7 causes approximately 63,000 acquired foodborne illnesses and 20 deaths in the United States annually. 1

In addition, the investigators pointed out that from 2009–2018, 32 confirmed or suspected outbreaks of E coli O157:H7 infections connected to contaminated leafy greens occurred in the United States and Canada.2

Symptoms for this infection can include diarrhea, stomach cramps and occasionally fever. About half of people with the infection will have bloody diarrhea. The onset is usually 3 to 4 days after people have been infected, but symptoms can occur any time between 1 and 14 days afterwards.3 There is no current treatment, and since the infection dehydrates the body, people are reminded to drink plenty of fluids.

The investigators point out there was one more outbreak in 2020, but they said there have been no further outbreaks, after that outbreak, and only a single clinical isolate associated with this strain has been identified by PulseNet.

CDC has classified the E coli O157:H7 strain as a reoccurring, emerging, or persistent (REP) strain with the designation REPEXH02.


1.Scallan E, Hoekstra RM, Angulo FJ, Tauxe RV, Widdowson MA, Roy SL, et al. Foodborne illness acquired in the United States—major pathogens. Emerg Infect Dis. 2011;17:7–15.

2. Marshall KE, Hexemer A, Seelman SL, Fatica MK, Blessington T, Hajmeer M, et al. Lessons learned from a decade of investigations of Shiga toxin–producing Escherichia coli outbreaks linked to leafy greens, United States and Canada. Emerg Infect Dis. 2020;26:2319–28.

3. Escherichia coli (E. coli) O157. NHS Inform. Updated May 23, 2023. Accessed September 6, 2023.,1%20and%2014%20days%20afterwards

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