December 18, 2020

CDC, public health and regulatory officials in several states, and the U.S. Food and Drug Administration (FDA) investigated a multistate outbreak of E. coli O157:H7 infections.

Public health investigators used the PulseNet system to identify illnesses that may have been 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 a standardized laboratory and data analysis method called whole genome sequencing (WGS). CDC PulseNet manages a national database of these sequences that are used to identify possible outbreaks. WGS gives investigators detailed information about the bacteria causing illness. In this investigation, WGS showed that bacteria isolated from ill people were closely related genetically. This means that people in this outbreak were more likely to share a common source of infection.

As of December 16, 2020, a total of 18 people infected with the outbreak strain of E. coli O157:H7 were reported from nine 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 September 2, 2020, to November 6, 2020. Ill people ranged in age from 8 to 71 years, with a median age of 28 years, and 72% were female. Of 16 ill people with information available, 6 were hospitalized. No deaths were reported.

WGS analysis of 15 isolates from ill people and 4 isolates from food did not predict resistance to any antibiotics. Standard antibiotic resistance testing by CDC’s National Antimicrobial Resistance Monitoring System (NARMS) laboratory is currently underway. These findings do not affect treatment guidance since antibiotics are not recommended for patients with E. coli O157:H7 infections.

Investigation of the Outbreak

State and local public health officials interviewed ill people to determine what they ate and other exposures in the week before they got sick. Of the 13 people interviewed, all reported eating or maybe eating various types of leafy greens, including romaine lettuce (9), spinach (9), and iceberg lettuce (7).

Laboratory testing identified the outbreak strain in a sample of Tanimura & Antle romaine lettuce in a single-head package, which was recalledexternal icon on November 6, 2020. However, investigators were unable to determine if any ill people in this outbreak got sick from eating the recalled product. No one specifically reported eating Tanimura & Antle romaine lettuce, and some people got sick before the “packed on” dates for the recalled products.

FDA conducted traceback investigations and worked with state partners to conduct inspections at several farms. However, none of the findings identified a common source in the distribution chain or linked the farms to the outbreak.

As of December 18, 2020, this outbreak is over. This outbreak ended before enough information was available for investigators to identify the likely source.