In all, 17 cases were confirmed, the most in California, with three, during the period, the CDC said.
The bacteria has been identified as E. coli O157, a strain which can be deadly for the elderly, infants, pregnant women and people with weak immune systems.
In the US, the infections have occurred in 13 states (California, Connecticut, Illinois, Indiana, Michigan, Nebraska, New Hampshire, New York, Ohio, Pennsylvania, Virginia, Vermont, and Washington state).
Most E. coli outbreaks are linked to meat products, but leafy greens are occasionally the cause.
At least two people were killed and dozens sickened by E. coli outbreaks in Canada and the United States that the authorities in Canada have linked to romaine lettuce. The source of the E. coli food poisoning is being investigated by FDA and CDC, along with public health officials in Canada. One person has died.
So far, authorities in Canada have pointed to Romaine lettuce as the likely source of the infection, while authorities in the United States are still now conducting an investigation that includes interviewing the infected people to determine the meals they consumed in the week prior to the onset of the illness.
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The CDC is conducting an investigation to determine the cause of the outbreak, and is looking at romaine "and other leafy greens", though according to Consumer Reports, the organization has confirmed that the strain of E. coli in the United States is "a virtual genetic match" with the Canadian strain.
The food-safety experts at Consumer Reports are advising consumers to avoid romaine all together and any products with romaine in them - such as salad blends and mixes - until the cause is found, identified and removed from store shelves. Consumer Reports, the nonprofit advocacy organization, said it was urging shoppers to avoid the lettuce as a precaution.
Symptoms of E. coli infection include fever, abdominal pain, bloody diarrhea, and, less commonly, a syndrome that can lead to kidney failure. "The trace-back information is always challenging too, because contamination can happen any place from the farm to the processing facility to the store".
According to CDC, preliminary results showed that the type of E coli making people sick in both countries was closely related genetically, meaning the ill people were more likely to share a common source of infection.
Most strains of E. coli are harmless to humans, but some can cause vomiting, diarrhea, severe stomach cramps and other symptoms.