Public Health Agencies Investigating Outbreak Linked to Romaine Lettuce

The Centers for Disease Control and Prevention (CD), public health and regulatory officials in several states, Canada, and the FDA are investigating a multistate outbreak of Shiga toxin-producing Escherichia coli O157:H7 (E. coli O157:H7) infections.

Public health investigators are using the PulseNet system to identify illnesses that may be part of this outbreak. PulseNet is the national subtyping network of public health and food regulatory agency laboratories coordinated by CDC. DNA fingerprinting is performed on E. coli bacteria isolated from ill people by using techniques called pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). CDC PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks. WGS gives a more detailed DNA fingerprint than PFGE. WGS performed on E. coli bacteria from ill people in this outbreak showed that the strains were closely related genetically. This means that the ill people were more likely to share a common source of infection.

As of Nov. 20, 2018, 32 people infected with the outbreak strain of E. coli O157:H7 have been reported from 11 states. A list of the states and the number of cases in each can be found on the Map of Reported Cases page.

Illnesses started on dates ranging from Oct. 8, 2018 to Oct. 31, 2018. Ill people range in age from 7 to 84 years, with a median age of 24. Sixty-six percent of ill people are female. Of 26 people with information available, 13 (50%) were hospitalized, including one person who developed hemolytic uremic syndrome, a type of kidney failure. No deaths have been reported.

Illnesses that occurred after Oct. 30, 2018, might not yet be reported due to the time it takes between when a person becomes ill with E. coli infection and when the illness is reported. This takes an average of two to three weeks

Epidemiologic evidence indicates that romaine lettuce is a likely source of this outbreak.

In interviews, ill people answered questions about the foods they ate and other exposures in the week before they became ill. Eleven (79%) of 14 people interviewed reported eating romaine lettuce. This percentage is significantly higher than results from a survey[PDF – 787 KB] of healthy people in which 47% reported eating romaine lettuce in the week before they were interviewed. Ill people reported eating different types of romaine lettuce in several restaurants and at home.

Whole genome sequencing (WGS) results showed that the E. coli O157:H7 strain isolated from ill people in this outbreak is closely related genetically to the E. coli strain isolated from ill people in a 2017 outbreak linked to leafy greens in the United States and to romaine lettuce in Canada. The current outbreak is not related to a recent multistate outbreak of E. coli O157:H7 infections linked to romaine lettuce. People in the spring outbreak were infected with E. coli O157:H7 bacteria with a different DNA fingerprint.

FDA and states are working to trace back romaine lettuce that ill people ate in the current outbreak. At this time, no common grower, supplier, distributor, or brand of romaine lettuce has been identified. CDC is advising that consumers not eat any romaine lettuce, and restaurants and retailers not sell any, until we learn more about this outbreak and the source of the contaminated lettuce.

Source: CDC