An investigation into a multistate Escherichia coli O157:H7 outbreak in the United States genetically linked to a similar outbreak in Canada—that health officials there have tied to romaine lettuce—is complex, and investigators at the US Centers for Disease Control and Prevention (CDC) are still looking for more evidence about the food source.
So far, 17 people from 13 states have been sickened in the outbreak, reflecting no new confirmed cases since the CDC's initial report on Dec 28. Officials today, however, said 1 death has been reported and 5 people have been hospitalized. Two patients have developed hemolytic uremic syndrome, a potentially fatal kidney complication.
Meanwhile in Canada, the Public Health Agency of Canada (PHAC) on Dec 28 reported one more case, raising the outbreak total to 41 cases in five eastern provinces. One death has been reported. The PHAC has linked the outbreak to romaine lettuce, based on interviews with sick patients, and has urged Canadians to temporarily avoid eating romaine lettuce, though no products have been recalled.
"There appears to be an ongoing risk of E. coli infections associated with the consumption of romaine lettuce in Canada's eastern provinces," the PHAC said in its latest update.
Probing for clues, more cases
Ian Williams, PhD, chief of the CDC's Outbreak Response and Prevention Branch, told CIDRAP News that the last illness onset was Dec 8, and though cases are still being reported, the pace of new reports appears to be slowing.
Whole-genome sequencing comparing the isolates from Canada and the United States has shown that the same strain is involved and that a common food source probably the source, Williams said.
He said so far, data aren't sufficient to link the US cases to romaine lettuce. The challenge here is that some sick patients recalled eating romaine lettuce and some didn't. Williams said investigators are in the process of reviewing information from shopper cards to look for food source clues and at sequencing information from more isolates to see if they are part of the outbreak.
Outbreaks possibly related to leafy greens are a challenge, no matter what, Williams said, because it can take 3 weeks to a month for a patient's illness to be identified as part of an outbreak, and it can be hard for people to remember the details of what they ate that far back.
Advocates urge romaine avoidance
Until a food source in the US outbreak has identified, food safety experts quoted in a Consumer Reports story yesterday advised consumers to temporarily avoid romaine lettuce. James Rogers, PhD, the group's director of food safety, said that although the source hasn't been identified, a greater degree of caution is needed, given that lettuce is almost always eaten raw.
He added that people in certain risk groups, such as young children, seniors, and people with underlying health conditions, be especially vigilant about avoiding romaine lettuce for the time being.
Jean Halloran, director of food policy initiatives at Consumers Union, a division of Consumer Reports, said the US Food and Drug Administration should follow Canada's example and immediately warn the public about the potential risk from romaine lettuce.
Dec 28 PHAC update
Jan 3 Consumer Reports story