November 30, 2018, Originally posted on CFAES website
I’m confused about the recent reports regarding leafy greens such as romaine lettuce. How is it that leafy greens can cause a foodborne illness?
Well, it is not the leafy greens themselves making people sick, but rather that they are the suspected source of pathogenic E. coli that has sickened some 58 people in Canada.
Several people in the United States have also become ill from a strain of E. coli that the Centers for Disease Control and Prevention says is closely related genetically to the strain that caused the outbreak in Canada. In fact, 24 such illnesses have been reported in 15 states, including Ohio, between Nov. 15 and Dec. 12, 2017, the CDC said this week.
The likely source of the outbreak in the United States appears to be leafy greens, the CDC said, noting that the agency has not identified a single type or brand associated with the outbreak. Their investigation is ongoing and includes interviewing sick people to determine what they ate in the weeks before their illnesses started, the agency said in a written statement.
“Preliminary results show 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 of infection,” the CDC statement said.
While Canadian authorities have warned about romaine lettuce consumption, the CDC states that “because we have not identified a source of the infections, CDC is unable to recommend whether U.S. residents should avoid a particular food.”
However, the CDC statement notes that “leafy greens typically have a short shelf life, and since the last illness started a month ago, it is likely that contaminated leafy greens linked to this outbreak are no longer available for sale.”
The illness in question is a multistate outbreak of Shiga toxin-producing E. coli O157:H7 infections. This strain of E. coli can produce a toxin that in some cases can cause serious illness, kidney failure or death. Thus far, at least five people in the United States have been hospitalized and one has died, according to the CDC. There has also been at least one death in Canada also, according to Consumer Reports.
So how can leafy greens become contaminated with E. coli?
If animal feces are in the field or soil in which the lettuce is grown, or if the lettuce comes into contact with water that contains the pathogen, E. coli can be transferred from the feces onto the lettuce. It can also be spread if a person who carries the bacteria doesn’t wash his or her hands after using the bathroom, and then processes or prepares food, said Abigail Snyder, an assistant professor and food safety field specialist in the College of Food, Agricultural, and Environmental Sciences (CFAES) at The Ohio State University.
It’s important to note that washing contaminated greens doesn’t remove all bacteria, food safety experts say. While cooking can eliminate E. coli, most people don’t cook their leafy green salads. For that reason, avoidance is sometimes recommended when the source of an outbreak is identified.
Symptoms of E. coli infection can begin as soon as 24 to 48 hours or as long as 10 days after eating contaminated food. Those symptoms include vomiting, severe or bloody diarrhea, and abdominal pain.
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Editor: This column was reviewed by Abigail Snyder, an assistant professor and food safety field specialist for CFAES.