U.S – By leveraging Whole Genome Sequencing (WGS), the U.S. Centers for Disease Control and Prevention (CDC) has unveiled a persistent and emerging threat lurking in our salad bowls: a strain of Escherichia coli O157:H7 known as REPEXH02.

This strain, believed to have surfaced in late 2015, has caused a series of foodborne illness outbreaks from 2016 to 2019, with the source traced back to romaine lettuce.

REPEXH02 is not your typical E. coli strain. Classified as a “Reoccurring, Emerging, and Persistent” or REP strain by the CDC, it has become a recurring nightmare in the world of food safety.

Responsible for multiple outbreaks between 2016 and 2019, this strain resurfaced in 2019, causing havoc with an outbreak linked to romaine lettuce grown in California’s Salinas Valley. This outbreak led to 167 cases of illness across 27 states, resulting in 85 hospitalizations.

But that’s not all. According to the CDC’s findings, a staggering 58 percent of recent E. coli infections can be attributed to vegetable row crops, with leafy greens taking center stage.

Leafy greens, often seen as the epitome of health, have become an unexpected source of danger. In late 2020, another outbreak associated with leafy greens rocked 19 states, sickening 40 people and leading to 20 hospitalizations, including four cases of hemolytic uremic syndrome (HUS).

The alarm bells started ringing after the late 2020 outbreak. The U.S. Food and Drug Administration (FDA), recognizing that foodborne illness outbreaks linked to leafy greens in California’s Central Coast region had become an annual occurrence since 2017, launched an in-depth investigation.

Leveraging WGS, the FDA managed to connect the dots, linking the implicated strain back to 2017 outbreaks. This strain, now dubbed REPEXH02, was named by the FDA as a “reasonably foreseeable hazard.”

Cattle connection

CDC identified cattle as the primary reservoir for E. coli O157:H7. The key to this strain’s persistence in leafy greens irrigation water appears to be the contamination of water sources by cattle fecal matter, which is then carried by floodwaters onto the fields.

However, further genomic characterization is needed to fully understand the mechanisms behind the emergence and persistence of this REP strain in various environments.

As the investigation continues, one thing is clear: the salad bowl may not be as innocent as it seems. The emergence of REPEXH02 serves as a stark reminder of the challenges in safeguarding the food supply chain.

It underscores the critical need for ongoing research, vigilant monitoring, and enhanced safety measures to ensure that the greens on our plates are as safe as they are nutritious.

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