June 20, 2024

Another Reoccurring E. coli O157:H7 Strain Linked to Leafy Greens

The CDC has identified another reoccurring E. coli O157:H7 strain that is linked to leafy greens outbreaks, according to the September issue of that agency’s Emerging Infectious Diseases Dispatch. This strain is in addition to the other reoccurring strain that was mentioned by the CDC in August’s Dispatch.

Another Reoccurring E. coli O157:H7 Strain Linked to Leafy Greens

Bacterial strains can be identified as reoccurring, emerging, or persisting (REP). Reoccurring strains repeatedly cause acute outbreaks, separated by periods when no illnesses are reported. Emerging strains are previously novel or rare strains that increasingly cause illness. And persisting strains cause illnesses consistently over a long time frame.

Whole genome sequencing, which maps a pathogen’s DNA, is used to find people sickened by the same bacterial strain. And WGS is used to find outbreaks of gastrointestinal diseases. When groups of illnesses caused by the same strain occur over longer time periods, they are called reoccurring. The number of illnesses, whether illnesses are increasing, high virulence, increased transmissibility, and whether or not the strain is the cause of large or frequent outbreaks are used to identify an REP strain.

E. coli O157:H7 causes about 63,000 domestically acquired foodborne illnesses, and 20 deaths every year in the United States. Contaminate leafy greens are recognized as a major source of E. coli O157″H7 illness and outbreaks. About 58% of E. coli illnesses in 2020, for instance, were linked to vegetable row crops that include leafy greens.

Six outbreaks spanning three years were studied by the researchers. Dates of isolation were from September 27, 2016 to January 3, 2020.

During the years of 2009 to 2018, 32 confirmed or suspected outbreaks of E. coli O157:H7 infections linked to contaminated leafy greens occurred in the United States and Canada. One of the worst, a large outbreak in late 2019, sickened at least 167 people in 27 states and hospitalized 85 patients. Ten people developed hemolytic uremic syndrome (HUS), a type of kidney failure. The lettuce was harvested in Salinas, California.

This reoccurring strain emerged in late 2015 and has been the source of online enteric illnesses since late 2016. After the analysis, an additional outbreak associated with this strain was found in late 2020, which sickened 40 people in 19 states. Twenty were hospitalized, and four developed hemolytic uremic syndrome.

No more outbreaks were detected after that one. The CDC has identified this strain as a reoccurring, emerging, or persistent strain with the designation REPEXH02.

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;29(9):1895-1899. https://doi.org/10.3201/eid2909.230069

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