Outbreaks of STEC O157:H7 Infections Spring Up in the US & Canada


Researchers are investigating outbreaks of Shiga toxin-producing E. coli in the United States and Canada, which may be linked to contaminated romaine lettuce.

The Centers for Disease Control and Prevention (CDC) have just announced that they are investigating a multistate outbreak of Shiga toxin-producing Escherichia coli (STEC) O157:H7 infections, the most commonly identified STEC in North America. A STEC O157:H7 outbreak has also sprung up in Canada, and has been linked back to contaminated romaine lettuce.

As of the media statement, released on December 28, 2017, a total of 17 illnesses have been reported, spanning 13 US states—California, Connecticut, Illinois, Indiana, Michigan, Nebraska, New York, Ohio, Pennsylvania, Virginia, and Washington.

The Public Health Agency of Canada reports that 41 cases of E. coli O157:H7 are currently under investigation, affecting individuals in 5 provinces; 17 of these individuals have required hospitalization and 1 individual has died. The majority of the individuals reported eating romaine lettuce prior to illness onset. “Individuals reported eating romaine lettuce at home, as well as in prepared salads purchased at grocery stores, restaurants, and fast food chains,” according to a recent public health notice. However, officials have yet to determine the source of the romaine lettuce responsible for these illnesses.

It is well known that E. coli bacteria are naturally found in the intestines of humans and animals alike. Most of these bacteria are harmless, but some of them are pathogenic, like the pathotype responsible for these outbreaks—STEC. There are many ways that lettuce can become contaminated with these bacteria; it can happen in the field via soil, contaminated water, animals, or manure that has not been correctly composted. Contamination can also occur in grocery stores, in refrigerators, or even from counters and cutting boards that have been contaminated with raw meat, poultry, or seafood.

Although investigators have not yet been able to identify the source of the US outbreak, preliminary genetic testing has found that “the type of E. coli making people sick in both countries is closely related genetically, meaning the ill people are more likely to share a common source,” according to the statement.

US investigators have been channeling their efforts into interviewing those who have fallen ill to identify what they consumed in the week prior to illness onset. Meanwhile, the CDC is “collecting information to determine whether there is a food item in common among sick people, including leafy greens and romaine,” according to the statement.

Without having identified the source of the outbreak in the United States, the CDC has not yet recommended avoiding a particular food. Meanwhile, Canadian health officials are warning all individuals residing in the 6 eastern provinces—Ontario, Quebec, New Brunswick, Nova Scotia, Newfoundland, and Labrador—to “consider consuming other types of lettuce, instead of romaine lettuce, until more is known about the outbreak and the cause of contamination.”

To stay up-to-date on the latest case counts associated with these outbreaks, as well as other ongoing food-borne outbreaks, be sure to check out the Contagion® Outbreak Monitor.

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