Romaine lettuce investigated in E. coli outbreak

You may be seeing romaine lettuce in the news a lot lately, the suspected culprit in a foodborne illness outbreak that has affected at least 57 people in the U.S. and Canada. But despite the headlines, the U.S. Centers for Disease Control and Prevention (CDC) says it’s too soon to pinpoint a single cause.

Even though no new cases have been reported since early December, it’s still too soon to say that the outbreak has truly ended, according to the chief of the CDC’s Outbreak Response and Prevention Branch, Ian Williams. This is especially true because the CDC is still uncertain that romaine lettuce is the source of the outbreak.

Although the CDC hasn’t officially identified a source, romaine lettuce began taking heat last week when Consumer Reports advised shoppers to avoid the product, citing it as the likely source of the reported E. coli O157:H7 cases. Canadian authorities have also recommended consumers avoid romaine lettuce for now.

While avoiding romaine lettuce may be wise while outbreak investigations are still ongoing, Williams points out to NBC that acting too soon to blame one product might leave people at risk in case the real source of bacteria turns out to be something different.

“We haven’t linked this to a specific food,” he said. “Not everyone says they had romaine. Some people say they have. Some people say they haven’t. We are trying to connect what people may have had in common across the entire country.”

Canadian investigators say they’ve scientifically traced the bacteria to romaine lettuce, but haven’t tied it to any farm, processing or distribution plant. The CDC has confirmed that the strain of E. coli detected in the U.S. is “a virtual genetic match” to the one in Canada. Investigations into other leafy greens are still ongoing.

Of the nearly 60 reported cases, there have been five hospitalizations and two deaths. The strain, E. coli O157:H7, belongs to a group known as Shiga toxin-producing E. coli, or STEC. These strains produce a toxin that can cause severe gastrointestinal illness and may lead to hemolytic uremic syndrome, or kidney failure.

Outbreak investigators use whole genome sequencing to find the source of the contamination, a process that reveals the entire DNA structure of an organism. With that information, it becomes possible to begin tracing where the bacteria came from by looking for the particular variant in other foods or food production sites.

Neogen is a leader in providing food safety solutions for microbiology and metagenomics.

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