December 22, 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 linked to leafy greens.

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 18, 2020, a total of 40 people infected with the outbreak strain of E. coli O157:H7 were reported from 19 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 August 10, 2020, to October 31, 2020. Ill people ranged in age from 1 to 85 years, with a median age of 33 years, and 60% were female. Of 34 ill people with information available, 20 people were hospitalized and 4 people developed hemolytic uremic syndrome (HUS), a type of kidney failure. No deaths were reported.

WGS analysis was conducted for isolates from 19 ill people; an isolate from 1 ill person was predicted to be resistant to ampicillin and amoxicillin-clavulanic acid, and 18 isolates from ill people were not predicted to be resistant to any antibiotics. Standard antibiotic susceptibility 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

Epidemiologic and traceback evidence showed that leafy greens were the likely source of this outbreak. Investigators were unable to identify a specific type or brand of leafy greens because people in this outbreak reported eating a variety of leafy greens and because different leafy greens are often grown, harvested, and processed together.

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 23 ill people interviewed, 22 reported eating or maybe eating a variety of leafy greens, including spinach (16) and romaine lettuce (15).

FDA completed traceback investigations for several types of leafy greens ill people reported eating. Several farms of interest were identified, but no single ranch was a common source of the leafy greens.

FDA and state partners conducted inspections on farms of interest and collected environmental samples. FDA is analyzing the samples and continuing their investigations to identify the root cause of this outbreak.

As of December 22, 2020, this outbreak is over.