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Abstract: In 2017 and 2019, five outbreaks of infections from multiple strains of Salmonella linked to the consumption of whole, fresh Maradol papayas were reported in the United States, resulting in 325 ill persons. Traceback, laboratory, and epidemiologic evidence indicated papayas as the likely vehicle for each of these outbreaks and identified the source of papayas. State and U.S. Food and Drug Administration (FDA) laboratories recovered Salmonella from papaya samples from various points of distribution, including at import entry, and conducted serotyping, pulsed-field gel electrophoresis, and phylogenetic analyses of whole genome sequencing data. Federal and state partners led traceback investigations to determine the source of papayas. Four different suppliers of papayas were linked by traceback and laboratory results to five separate outbreaks of Salmonella infections associated with papayas. In 2017, multiple states tested papaya samples collected at retail, and Maryland and Virginia investigators recovered strains of Salmonella associated with one outbreak. FDA collected 183 papaya samples in 2017, and 11 samples yielded 62 isolates of Salmonella. Eleven serotypes of Salmonella were recovered from FDA papaya samples, and nine serotypes were closely related genetically by pulsed-field gel electrophoresis and whole genome sequencing to clinical isolates of four outbreaks, including the outbreak associated with positive state sample results. Four farms in Mexico were identified, and their names were released to the general public, retailers, and foreign authorities. In 2019, FDA collected 119 papaya samples, three of which yielded Salmonella; none yielded the 2019 outbreak strain. Investigators determined that papayas of interest had been sourced from a single farm in Campeche, Mexico, through traceback. This information was used to protect public health through public guidance, recalls, and import alerts and helped FDA collaborate with Mexican regulatory partners to enhance the food safety requirements for papayas imported from Mexico., (Published 2021 by the International Association for Food Protection Not subject to U.S. Copyright. This is an open access article.)

Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. No potential conflicts of interest were disclosed.

On 10 August 2016, the Maricopa County Department of Public Health identified culture-confirmed Salmonella enterica serotype Javiana isolates from two persons who reported eating at a seafood restaurant; seven additional cases were reported by 15 August. We investigated to identify a source and prevent further illness. We interviewed persons with laboratory-reported Salmonella Javiana infection. Pulsed-field gel electrophoresis (PFGE) and whole genome sequencing of isolates were performed. A case was defined as diarrheal illness in a person during July to September 2016; confirmed cases had Salmonella Javiana isolate yielding outbreak-related PFGE patterns; probable cases had diarrheal illness and an epidemiologic link to a confirmed case. Case finding was performed (passive surveillance and identification of ill meal companions). A case-control study assessed risk factors for Salmonella Javiana infection among restaurant diners; control subjects were chosen among meal companions. No restaurant workers reported illness. Foods were reportedly cooked according to the Food Code. Food and environmental samples were collected and cultured; Salmonella Javiana with an indistinguishable PFGE pattern was isolated from portioned repackaged raw shrimp, halibut, and a freezer door handle. We identified 50 Salmonella Javiana cases (40 confirmed and 10 probable); illness onset range was from 22 July to 17 September 2016. Isolates from 40 patients had highly related PFGE patterns. Thirty-three (73%) of 45 patients interviewed reported eating at the restaurant. Among 21 case patients and 31 control subjects, unfried cooked shrimp was associated with illness (odds ratio, 6.7; 95% confidence interval, 1.8 to 24.9; P = 0.004). Among restaurant diners, laboratory and case-control evidence indicated shrimp as the possible outbreak source; poor thermal inactivation of Salmonella on shrimp is theorized as a possible cause. Cross-contamination might have prolonged this outbreak; however, the source was not identified and highlights limitations that can arise during these types of investigations.

Foodborne salmonellosis causes an estimated 1 million illnesses and 400 deaths annually in the United States (1). Salmonella Anatum is one of the top 20 Salmonella serotypes in the United States. During 2013-2015 there were approximately 300-350 annual illnesses reported to PulseNet, the national molecular subtyping network for foodborne disease surveillance. In June 2016, PulseNet identified a cluster of 16 Salmonella Anatum infections with an indistinguishable pulsed-field gel electrophoresis (PFGE) pattern from four states.* In April 2016, the same PFGE pattern had been uploaded to PulseNet from an isolate obtained from an Anaheim pepper, a mild to medium hot pepper. Hot peppers include many pepper varieties, such as Anaheim, jalapeño, poblano, and serrano, which can vary in heat level from mild to very hot depending on the variety and preparation. This rare PFGE pattern had been seen only 24 times previously in the PulseNet database, compared with common PFGE patterns for this serotype which have been seen in the database hundreds of times. Local and state health departments, CDC, and the Food and Drug Administration (FDA) investigated to determine the cause of the outbreak. Thirty-two patients in nine states were identified with illness onsets from May 6-July 9, 2016. Whole-genome sequencing (WGS) was performed to characterize clinical isolates and the Anaheim pepper isolate further. The combined evidence indicated that fresh hot peppers were the likely source of infection; however, a single pepper type or source farm was not identified. This outbreak highlights challenges in reconciling epidemiologic and WGS data, and the difficulties of identifying ingredient-level exposures through epidemiologic investigations alone.