2020 E. coli Outbreak Linked to Unknown Source 1 – Investigation Updates

October 28, 2020

CDC, public health and regulatory officials in several states, and the U.S. Food and Drug Administration (FDA) are investigating a multistate outbreak of 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 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 are more likely to share a common source of infection.

As of October 28, 2020, a total of 21 people infected with the outbreak strain of E. coli O157:H7 have been reported from eight 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 June 6, 2020, to October 5, 2020. Ill people range in age from  2 to 75 years, with a median age of 24 years. Sixty-seven percent of ill people are female. Of 16 ill people with information available, 8 hospitalizations have been reported, including 1 person who developed hemolytic uremic syndrome (HUS), a type of kidney failure. One death has been reported from Michigan.

Illnesses might not yet be reported due to the time it takes between when a person becomes ill and when the illness is reported. This takes an average of 2 to 4 weeks. Please see the Timeline for Reporting Cases of E. coli O157 Infection for more details.

Investigation of the Outbreak

Investigators are reviewing different types of data to identify the source of this outbreak.

State and local public health officials are interviewing ill people to determine what they ate and other exposures in the week before their illness started.

Several ill people have been identified as part of an illness cluster at a restaurant. An illness cluster is defined as two or more people from different households who report eating at the same restaurant location, attending a common event, or purchasing food at the same grocery store in the week before becoming ill. Investigating illness clusters can provide critical clues about the source of an outbreak. If several unrelated ill people ate or shopped at the same location of a restaurant or store within several days of each other, it suggests that the contaminated food item was served or sold there.

The strain of E. coli O157:H7 causing illness in this outbreak has previously caused outbreaks linked to different sources, including an outbreak linked to romaine lettuce in 2018. However, food linked to a previous outbreak alone is not enough to prove a link in another outbreak of the same strain. This is because different foods can be contaminated by the same strain of bacteria.

Public health officials are continuing to interview ill people and the FDA is conducting farm inspections, sampling, and traceback investigations.

A specific food item has not yet been identified as the source of this outbreak. CDC is not advising people avoid any particular food at this time.

CDC will provide updates when more information becomes available.