The outbreak is responsible for 66 infections and two deaths in the two countries.
The Public Health Agency of Canada (PHAC) said it was no longer advising people to consider consuming other lettuce types, instead of romaine.
No individuals have illness onset dates after 12 December so the outbreak appears to be over. The cause of contamination was not identified.
A total of 42 cases in five provinces
There were 42 cases in five eastern provinces: Ontario (eight), Quebec (15), New Brunswick (five), Nova Scotia (one) and Newfoundland and Labrador (13). Seventeen individuals were hospitalized and one died.
Those who became ill were between the ages of three and 85 and the majority (74%) were female.
PHAC said ‘most’ of the sick people ate romaine lettuce before illnesses either at home or in prepared salads from grocery stores, restaurants and fast food chains.
All romaine lettuce samples tested by the Canadian Food Inspection Agency were negative for E. coli O157.
Whole genome sequencing (WGS) showed the STEC O157:H7 strain from ill people in the US was closely related genetically to the strain from those infected in Canada.
Outbreak affects 24 people in 15 states
The US Centers for Disease Control and Prevention (CDC) said the outbreak has affected 24 people in 15 states. Among 18 ill people with information available, nine were hospitalized.
One person in California has died and two have developed hemolytic uremic syndrome (HUS), a type of kidney failure.
The last reported illness started on 12 December.
CDC said the likely source appears to be leafy greens but no specific type has been identified as being eaten by people who became ill.
Leafy greens have a short shelf life, and since the last illness started a month ago, it is likely contaminated items linked to the outbreak are no longer on sale, it added.
Of 13 people interviewed all reported eating leafy greens.
“Five of nine ill people specifically reported eating romaine lettuce,” said CDC.
“This percentage was not significantly higher than results from a survey of healthy people in which 46% reported eating romaine lettuce in the week before they were interviewed.
“Based on this information, US health officials concluded that ill people in this outbreak were not more likely than healthy people to have eaten romaine lettuce.”
Ill people also ate different types and brands of romaine lettuce and no common supplier, distributor or retailer has been identified as the possible outbreak source.
Likely suspect leafy greens no longer on market
The US Food and Drug Administration (FDA) said as illnesses had illness onsets in late November and early December it suggests suspect leafy greens are likely no longer in the food supply.
FDA’s outbreak investigation team is trying to determine what ill people ate, where they bought it, and the distribution chain to see if there’s a common food or point where contamination occurred.
“At this point, we have not identified a common or single point of origin for the food that made people ill. We want to make sure the information we provide is accurate and when we have information that consumers can use – such as any foods to avoid – we will share it immediately.”
Congresswoman Rosa DeLauro welcomed the update but said seven additional cases underscore the importance of completing the investigation in a timely fashion.
“CDC must proceed with their investigation quickly to determine the source of this outbreak, and FDA should work hand-in-hand with them to prevent further outbreaks. The American people should not be left wondering for weeks on end if the food they are eating is safe.”
DeLauro had earlier written to Brenda Fitzgerald, CDC director, demanding an update on the outbreak.
“CDC confirmed the outbreak on December 28 - almost a month and a half after the first infection. CDC’s stunning lack of guidance to consumers regarding this outbreak is unconscionable.”
Produce associations and Consumer Reports comment
Five produce associations said both governments have concluded the food responsible for the outbreak is no longer on the market.
“Public health agencies in both the US and Canada are informing consumers that there are no concerns about consuming any particular food, while they continue their investigations into what caused this E. coli O157:H7 outbreak that began in November,” said United Fresh Produce Association; Arizona and California LGMAs; Canadian Produce Marketing Association; Produce Marketing Association and Western Growers.
The groups had previously said no public agency had contacted any romaine lettuce grower, shipper or processor and requested they stop shipping or recall product in the marketplace.
Consumer Reports' food safety experts advised consumers to stop eating romaine lettuce.
Jean Halloran, director of Food Policy Initiatives at Consumers Union, said: “Right now the CDC is saying it could be other leafy greens, but until we have more corroborating evidence, we continue to think it prudent to avoid romaine lettuce for now.”
James E. Rogers, director of food safety research and testing at Consumer Reports, said CDC's position could give consumers a false sense of security.
“Without knowing exactly what caused this outbreak, we risk seeing a new batch of tainted product come onto the market. For instance, if the equipment at a processing plant is contaminated with E. coli O157:H7, new product could become a source of further infections.”