Multistate Outbreak of <i>Salmonella</i> Thompson Infections Linked to Diced Onions—2023

Since 2020, more than 2000 illnesses have been linked to foodborne outbreaks associated with onions. In 2023, the U.S. Food and Drug Administration (FDA), the Centers for Disease Control and Prevention, and state partners investigated a multistate outbreak of <i>Salmonella</i> Thompson infections linked to diced onions grown and processed in California. The outbreak resulted in 80 ill people, 18 hospitalizations, and one death reported in 23 states. FDA conducted a traceback investigation that included three illness clusters comprised of five total ill people from four Long-Term Care Facilities. Three inspections, each accompanied by sampling, were conducted at Processor A, Grower A, and Packing Shed A, respectively. The FDA analyzed 18 samples, six of which yielded <i>Salmonella</i> spp. isolates. Isolates recovered from water, sediment, and piping below irrigation equipment, near the growing environment, matched the outbreak strain. Additional isolates recovered from environmental samples matched eight <i>Salmonella</i> Saintpaul clinical isolates from 2022, four <i>Salmonella</i> Infantis clinical isolates from four states from 2022 to 2023, and two unrelated <i>Salmonella</i> Newport clinical clusters from 2021 to 2023. Laboratory, traceback, and epidemiological evidence indicated onions grown in three specific fields as the source of the outbreak, suggesting that the outbreak strain was present at the farm level, established in the soil, and potentially disseminated through agricultural water. Further processing into diced onions could have also spread and/or amplified the pathogen in the product due to the practices and conditions at the processor. This investigation highlighted the importance of outreach and education to enhance onion industry food safety practices and prevent future outbreaks. It also emphasized the need for focused research on onion industry practices, including growing, harvesting, curing, processing, packing, and holding.