Outbreaks of foodborne illness are fraught with uncertainties.
It’s OK to admit, to do the best with the info available, and get on with things.
On January 10, 2018, the Public Health Agency of Canada reported that an outbreak of Shiga toxin-producing E. coli O157:H7 infections (STEC O157:H7) they had identified was linked to romaine lettuce appears to be over.
As of January 10, 2018, there were 42 cases of E. coli O157 illness reported in five eastern provinces. Individuals became sick in November and early December 2017. Seventeen individuals were hospitalized. One individual died.
In the United States, the Centers for Disease Control, several states, and the U.S. Food and Drug Administration continue to investigate a multistate outbreak of 24 STEC O157:H7 infections in 15 states. Since CDC’s initial media statement on December 28, seven more illnesses have been added to this investigation. The last reported illness started on December 12, 2017.
The likely source of the outbreak in the United States appears to be leafy greens, but officials have not specifically identified a type of leafy greens eaten by people who became ill. 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. Canada identified romaine lettuce as the source of illnesses there, but the source of the romaine lettuce or where it became contaminated is unknown.
Whole genome sequencing (WGS) showed that the STEC O157:H7 strain from ill people in the United States is closely related genetically to the STEC O157:H7 strain from ill people in Canada. WGS data alone are not sufficient to prove a link; health officials rely on other sources of data, such as interviews from ill people, to support the WGS link. This investigation is ongoing. Because CDC has not identified a specific type of leafy greens linked to the U.S. infections, and because of the short shelf life of leafy greens, CDC is not recommending that U.S. residents avoid any particular food at this time.
In the United States, a total of 24 STEC O157:H7 infections have been reported. Among the 18 ill people for whom CDC has information, nine were hospitalized, including one person in California who died. Two people developed hemolytic uremic syndrome, a type of kidney failure.
The Public Health Agency of Canada identified romaine lettuce as the source of the outbreak in Canada. In the United States, the likely source of the outbreak appears to be leafy greens, but health officials have not identified a specific type of leafy greens that sick people ate in common.
State and local public health officials continue to interview sick people in the United States to determine what they ate in the week before their illness started. Of 13 people interviewed, all 13 reported eating leafy greens. Five (56%) of nine ill people specifically reported eating romaine lettuce. 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, U.S. health officials concluded that ill people in this outbreak were not more likely than healthy people to have eaten romaine lettuce. Ill people also reported eating different types and brands of romaine lettuce. Currently, no common supplier, distributor, or retailer of leafy greens has been identified as a possible source of the outbreak. CDC continues to work with regulatory partners in several states, at the U.S. Food and Drug Administration, and the Canadian Food Inspection Agency to identify the source.
Although the most recent illness started on December 12, there is a delay between when someone gets sick and when the illness is reported to CDC. For STEC O157:H7 infections, this period can be two to three weeks. Holidays can increase this delay. Because of these reporting delays, more time is needed before CDC can say the outbreak in the United Stated is over. This investigation is ongoing.