November 4, 2020

CDC, public health and regulatory officials in several states, and FDA investigated a multistate outbreak of Salmonella Stanley infections.

Public health investigators used the PulseNet system to identify illnesses that were 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 Salmonella 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 likely to share a common source of infection.

A total of 55 people infected with the outbreak strain of Salmonella Stanley were reported from 12 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 January 21, 2020, to September 19, 2020. Ill people ranged in age from 2 to 74 years, with a median age of 28. Fifty-seven percent of ill people were female. Of 48 ill people with information available, 6 hospitalizations were reported. No deaths were reported.

Whole genome sequencing analysis of 35 bacterial isolates from ill people did not predict any antibiotic resistance. Standard antibiotic susceptibility testing by CDC’s National Antimicrobial Resistance Monitoring System (NARMS) laboratory is underway.

Investigation of the Outbreak

Epidemiologic, laboratory, and traceback information showed that wood ear mushrooms distributed by Wismettac Asian Foods, Inc., were the 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. Of 23 people with information, 22 (96%) reported eating ramen at a restaurant in the week before their illness started. Several people reported eating at the same ramen restaurants, showing they may have been part of illness clusters.

A foodborne illness cluster is defined as two or more people who do not live in the same household who report eating at the same restaurant location, attending a common event, or shopping at the same location of a 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.

Five illness clusters were identified at restaurants serving ramen in three states. Ten (91%) of the 11 ill people linked to restaurant clusters reported eating wood ear mushrooms or ramen containing wood ear mushrooms in the week before their illness started.

FDA and states conducted a traceback investigation from four of the restaurants with illness clusters to identify the source of the wood ear mushrooms eaten by ill people. Traceback determined that Wismettac Asian Foods, Inc., supplied wood ear mushrooms (dried fungus) to these restaurants.

On September 23, 2020, Wismettac Asian Foods recalledexternal icon dried fungus due to possible Salmonella contamination. On October 1, 2020, the California Department of Public Health identified the outbreak strain of Salmonella Stanley in recalled dried fungus samples.

As of November 4, 2020, this outbreak appears to be over.