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Outbreak Investigation

Salmonella Outbreak Linked to Cantaloupe Products

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A new outbreak involving imported whole cantaloupe and downstream sliced/cubed cantaloupe containing products contaminated with Salmonella was posted by CDC and FDA officials on November 17, 2023. Currently, 99 individuals in the U.S. and 63 in Canada have reported illness. Initially, whole genome sequencing showed that Salmonella Sundsvall was closely related
genetically to the bacteria collected from those reporting illness. Salmonella Soahanina and Oranienburg are now also identified as outbreak strains detected in the imported product by Canadian officials. Numerous whole and sliced/cubed cantaloupe containing products have been recalled from major retailers across the U.S. and Canada.

Outbreaks involving cantaloupe are not uncommon. Contamination often begins in the field and is then spread to process/packaging facilities where it can become established in the environment. If proper controls are not in place, pathogens can spread to the edible fruit when cut and processed into ready-to eat products. This can spread to further products when cut cantaloupe is used as an ingredient. Investigation reports from three of the outbreaks highlighted in the table below are available from FDA.

Year Pathogen Product Illnesses Country
2022Salmonella Typhimuriumwhole cantaloupe87USA
2019Salmonella Javianacut fruit mix containing cantaloupe165USA
2019Salmonella Carraucut melon including cantaloupe137USA
2018Salmonella Adelaidecut melon including cantaloupe77USA
2012Salmonella Typhimurium
and Salmonella Newport		whole cantaloupe261USA
2012Listeria monocytogeneswhole cantaloupe147USA
2011Salmonella Panamawhole cantaloupe20USA
2008Salmonella Litchfieldwhole cantaloupe51USA

The following describes FDA’s investigational findings from their most recent report and provides their recommendations to growers of melons and similar produce. In August 2022, a CDC epidemiological investigation and traceback data identified a multistate cluster of Salmonella Typhimurium illnesses in the upper Midwest indicating melons as a potential source of exposures. The outbreak was traced to cantaloupe and resulted in eighty-seven illnesses and thirty-two hospitalizations across eleven states.

The FDA utilized traceback data to identify a common packinghouse of suspect cantaloupes associated with the outbreak. However, there was no convergence to a single shipment of products. Three farms in southern Indiana that supplied the common packinghouse were identified as potential sources of cantaloupe. Around the growing locations other commodities were grown such as grain, oilseed, and beans; interspersed with various vegetable crops, including melons; and several poultry feeding
operations. Heavy rains had also occurred in the growing region in late July resulting in floods.

Sampling of the packing house, the three farms, and the surrounding lands resulted in numerous findings of Salmonella, but only one of the farms produced an isolate genetically related to the outbreak strain (i.e., having an intermediate level of differences in genomes but not a genetic match). The results suggest that Salmonella presence is a reoccurring issue that may impact the safety of melons grown in this region.

FDA provides the following recommendations/requirements to producers of melons and similar produce.

  • Review current conditions and practices to determine whether they are adequate or if additional
    prevention measures are warranted.
  • Understand previous land use to identify and address potential sources of pathogens that may
    affect their farming operations.
  • Assess risks that may be posed by adjacent and nearby land uses, especially as it relates to the
    presence of livestock, poultry, and the interface between farmland, and other agricultural areas.
  • Consider additional tools such as pre-harvest and/or post-harvest sampling and testing of
    products to help inform the need for specific prevention measures.
  • Poultry manure, while valued for its fertilizer value, is a known reservoir for Salmonella
    spp. Proper application of a manure that has been treated with a validated and verified process
    to reduce pathogens (e.g., composting with time and temperature measurements) can
    significantly reduce the potential for the integration of Salmonella or other human pathogens into
    soils (as compared to the use of raw manures).
  • Inspect, maintain, and clean and, when necessary and appropriate, sanitize all food contact
    surfaces of equipment and tools used as frequently as necessary to protect against contamination.
  • When appropriate, use EPA-approved products according to the label for cleaning and sanitizing.
  • Inconsistent adherence to or deviation from existing SOPs for cleaning and sanitizing by farms can
    affect produce safety. Effective communication on farms about SOPs and any changes to those
    SOPs can help ensure that food safety practices are being followed.
  • Root cause analyses may be useful in identifying for growers how human pathogen sources in the
    broader agricultural environment may contribute to contamination.
  • Improve traceability through increased digitization, interoperability, and standardization of
    traceability records which would expedite traceback and help remove contaminated product from
    the marketplace more quickly, thereby preventing further illnesses. This is not only important for
    growers, but also critical for shippers, manufactures, and retailers as well, to improve overall
    traceability throughout the supply chain.

IAFP 2023 – Symposium Discusses the Investigation of Ambiguous Outbreaks

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A symposium at IAFP 2023 (S64), “Investigating Ambiguous Outbreaks and Adverse Events” sponsored by the Institute for the Advancement of Food and Nutrition Science (IAFNS) Food Microbiology Committee discussed the topic of “ambiguous outbreaks,” those outbreaks of foodborne illness for which definitive sources and/or pathogens targets are not known.

The FDA will issue a public health advisory for outbreak investigations that result in specific, actionable steps for consumers to take to protect themselves. However, some outbreak and adverse event investigations may not conclusively identify a source or reveal any contributing factors. Actionable steps for consumers are not available. FDA maintains a list of outbreak and adverse event (self-reported) investigations managed by their CORE Response teams. Although an investigation may reveal a particular product or product category as a possible source of illness, the FDA will not publicly name a specific product until there is sufficient epidemiological evidence to implicate that product as a cause of illness or an adverse event.

Many investigations do not identify a pathogen or food vehicle responsible for an outbreak or self-reported illnesses in an adverse event despite extensive testing for numerous potential microbial and chemical adulterants. What learnings can be taken from these investigations that could improve resolution and contribute to an improved prevention strategy? This symposium delved into the question. A recording of the symposium will be available from IAFP.

Speakers discussed improved investigational approaches and tools, the use of Root Cause investigation and analysis to uncover factors leading to attribution, improved outbreak communication strategies for reaching consumers and industry, and new areas of research.

Ambiguous outbreaks can be grouped into one or more of the following categories: outbreaks with a known source and unknown agent, a known agent and unknown source, or an unknown agent and unknown source. Dr. Craig Hedberg, University of Minnesota, discussed improved investigational tools to detect and identify a causative agent such as culture independent diagnostic tests (CIDT) and whole genome sequencing. He also reviewed advances in epidemiological and environmental assessments that improve the chances of making connections between an illness and the source when studying outbreaks for which definitive sources and/or pathogens targets are not known.

Dr. Tim Jackson, FDA, reviewed reasons why the root cause of an outbreak is often ambiguous. Investigations into outbreaks are usually retrospective, analytical testing is statistically limited and often inconclusive, and some foods with short shelf lives may not be available for analysis. Additionally, there may be limited tools for analysis of some causative agents. With multi-component or assembled products, processes and supply chains may be complex with a variety of growers/suppliers, manufacturers, retailers, and distributors. Accurate and precise traceability programs are essential to the evaluation of underlying causes. Dr. Jackson discussed the tools available for root cause investigation and analysis and provided examples of how they have been used in the resolution of outbreaks.


Michael Vasser, CDC, examined the impact of reoccurring, emerging, and persisting (REP) strains on ambiguous outbreaks. Some enteric bacterial strains cause acute outbreaks linked to specific sources. Other strains that are closely related by whole genome sequencing, referred to as REP strains, can reoccur and periodically cause acute outbreaks. They can also emerge and increase in frequency or persist and cause illnesses over periods of months or years, despite investigation and prevention efforts. They do not present as typical acute outbreaks. While illnesses caused by REP strains may be associated with a common reservoir or source, the linkage is often inferred but not proven. Mr. Vasser commented that, in fact, most illnesses reported through PulseNet are not linked to a source (90% of isolates do not have an assigned cluster code). REP strains could actually be the cause of a larger fraction of illnesses than
typical outbreaks. Investigation of REP strains will create opportunities to characterize new sources of enteric disease and develop novel prevention approaches.


Mitzi Baum, STOP Foodborne Illness, discussed the critical need for improved communication channels to the public and industry when outbreaks occur. Stop Foodborne Illness is a non-profit public health organization in the United States dedicated to the prevention of illness and death from foodborne pathogens. The organization was founded in 1993 following an E. coli O157:H7 outbreak in California and the Pacific Northwest. While ambiguity in investigations does occur, it is essential that public health officials provide relatable and actionable information to consumers in these circumstances.



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