Fresh hot peppers were the likely source of infection but a single type or source farm could not be identified.
Among 25 patients for whom such information was available, eight (32%) were hospitalized but no deaths were reported.
Outbreak strain found in Anaheim pepper
The outbreak strain was isolated from an imported Anaheim pepper before identification of cases and as part of routine surveillance of produce but patients did not report eating this type of pepper.
The pepper was collected from a Mexican consolidator/grower, which supplied two restaurants visited by patients in the outbreak.
However, seven additional samples of hot peppers, including serrano, habanero, jalapeño and bell peppers from the firm were all negative for Salmonella.
FDA placed Elias Gerardo Gonzalez Valdez on import alert for Anaheim peppers and there were only two outbreak-associated illnesses reported after it was issued.
The routine surveillance involves collection of 1,600 hot pepper samples (320 domestic and 1,280 of international origin).
As of April, one out of 310 domestic samples was positive for Salmonella and 44 of 1,255 imported samples were positive.
In June 2016, PulseNet identified a cluster of 16 Salmonella Anatum infections with an indistinguishable pulsed-field gel electrophoresis (PFGE) pattern from four states.
This rare PFGE pattern had been seen only 24 times previously in the PulseNet database.
Salmonella Anatum is one of the top 20 serotypes in the US, with 300-350 illnesses reported to PulseNet annually during 2013-2015.
Seven of 14 interviewed patients ate at Mexican-style restaurants in the week preceding illness onset. Illness onsets were from May 6-July 9.
Commonly reported foods eaten in the week before illness included tomatoes (71% of respondents); pork (64%); avocado/guacamole (57%); jalapeños (36%); and cantaloupe (36%).
The only food reported significantly more frequently than expected among patients was avocado/guacamole but it was not possible to do a comparison with jalapeños.
Among 18 patients for whom information was available, 14 reported eating or possibly eating fresh hot peppers, or reported having an item containing fresh hot peppers.
“The epidemiologic investigation relied on review of restaurant-specific recipes, because pepper varieties were difficult to identify when used as ingredients in foods, particularly when prepared at restaurants,” said researchers.
“In addition, because many common ingredients are consumed in Mexican-style meals, it was difficult to narrow a hypothesis based on epidemiologic information alone.”
Nine patients ate peppers at restaurants, two ate peppers at restaurants and at home and three did not specify a location. Among the 14 patients who had eaten peppers, 11 reported eating or possibly eating jalapeños.
FDA conducted traceback from three restaurants in Minnesota and Texas where patients reported eating. Two received peppers from Elias Gerardo Gonzalez Valdez in Mexico and the third received peppers from various firms in Mexico but had received peppers from that firm before the outbreak.
“Although only two of the three restaurants included in the informational traceback investigation received peppers from the same consolidator/grower, it is possible that contaminated peppers cross-contaminated other foods or materials along the supply chain, providing a mechanism for the outbreak strain to reach the third restaurant.”
“Multistate Outbreak of Salmonella Anatum Infections Linked to Imported Hot Peppers - United States, May-July 2016”
Authors: Hassan R, Rounds J, Sorenson A, et al