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Multiyear Listeria Outbreak Attributed to Peaches, Plums, &Nectarines

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Whole peaches, plums, and nectarines (i.e. stone fruit) have been implicated in a multistate outbreak of Listeria monocytogenes infections. Initially, an epidemiological investigation indicated
people in this outbreak were 18 times more likely to eat peaches, plums, or nectarines. Subsequent sampling and testing of 2lb bagged peaches from the supplier were found positive by FDA and linked with whole genome sequencing to the outbreak strain. Further analysis indicates that this outbreak has led to one death and eleven illnesses occurring as far back as August 2018.


This is not the first outbreak associated with stone fruit. An outbreak involving Salmonella Enteritidis contaminated peaches occurred in 2020 causing 101 reports of illness. In a 2014 outbreak, the first cases of listeriosis involving contaminated stone fruit (i.e. whole peaches, nectarines, plums, and pluots) were reported. Pathogens generally persist on the contaminated fruit surface (i.e. skin) and can cause illness if not properly sanitized before consumption.

An investigation report for the 2020 outbreak published by FDA examined the potential sources and routes of Salmonella product contamination from associated peach orchards and packing lines. Environmental samples were collected from the packing houses, product samples (peaches) from the packing houses and orchards, and peach tree leaves from the orchards during the investigations. All tested negative for presence of the outbreak strain. This may have been due to subsequent cleaning/sanitization and review/update of food safety programs that occurred during the product recall. However, multiple Salmonella isolates from product and leaf sampling genetically resembled previous chicken and cattle isolates, not associated with any known foodborne illnesses. FDA hypothesized that the adjacent animal operations (both poultry and cattle) were a likely contributing factor to the Salmonella Enteritidis outbreak – with fugitive dust as one possible route of product contamination.

Similar to Salmonella, L. monocytogenes is ubiquitous in nature. It can spread from the growing
environment to harvesting and packing equipment, establishing itself in the processing environment if poor sanitation practices are used. A 2014 outbreak involving L. monocytogenes contaminated whole apples found numerous locations in a processing facility positive for the pathogen where environmental surfaces came into contact with product.


Whole fruits, such as peaches, are considered a raw agricultural commodity and need to comply with regulations set forth in the Produce Safety Rule for the safe growing, harvesting, packing, and holding of fruits and vegetables grown for human consumption. Guidance to meet these requirements is available from FDA.

IFSAC Releases Foodborne Illness Source Attribution Estimates for 2021

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The model estimated percentage of foodborne Salmonella, Escherichia coli O157, and Listeria
monocytogenes illnesses in 2021 attributed to each of 17 food source categories was recently released by the Interagency Food Safety Analytics Collaboration (IFSAC) made up of members from CDC, FDA, and USDA-FSIS.

The IFSAC group was established in 2011 to improve coordination of federal food safety analytic efforts and address priorities for food safety data collection, analysis, and use. IFSAC analyzes foodborne illness outbreak data for priority pathogens and specific foods and food categories responsible for foodborne illnesses in the United States. The data are analyzed by calendar
year and released in annual reports as part of ongoing efforts to understand sources of foodborne illness in the United States. The CDC estimates that together these priority pathogens — Salmonella, E. coli O157, Campylobacter, and L. monocytogenes — cause nearly two million cases of foodborne illnesses in the U.S. each year.

Foodborne illness source attribution estimates were generated from surveillance data collected between 1998 through 2021. The dataset included 1,322 outbreaks in which the confirmed or suspected implicated food or foods could be assigned to a single food category: 987 caused or suspected to be caused by Salmonella, 275 by E. coli O157, and 60 by L. monocytogenes. These include 46 outbreaks caused by
multiple serotypes of Salmonella. IFSAC assessed which categories of foods were most responsible for Salmonella, E. coli O157, and L. monocytogenes infections. These pathogens were chosen because of the frequency or severity of the illnesses they cause, and because targeted interventions can have a major impact in reducing them. The implicated foods were divided into 17 categories for the analysis. The method used for estimation gave the greatest weight to the most recent five years of outbreak data (2016–2020). The top food categories associated with each pathogen are detailed below.

For Salmonella, over 75% of illnesses were attributed to seven food categories including chicken, fruits, pork, seeded vegetables (such as tomatoes), other produce (such nuts), beef, and turkey. Estimated Salmonella illnesses were more evenly distributed across food categories than illnesses from E. coli O157, and L. monocytogenes.

Over 80% of E. coli O157 illnesses were attributed to vegetable row crops, such as leafy greens (lettuce, spinach), celeries, broccoli, and beef. Vegetable row crops had a significantly higher estimated attribution percentage than all other categories followed by beef.

For L. monocytogenes, over 75% of illnesses were attributed to dairy (fluid milk, hard and soft cheese), fruits (melons, apples, cherries, berries, mangoes, avocados), and vegetable row crops. However, the small total number of outbreaks (60) in the data set caused this estimate to be less reliable than estimates for the other pathogens.


The attribution of Salmonella illnesses to multiple food categories suggests that multiple types of
interventions are required to reduce illnesses from these pathogens. In contrast, the majority of E. coli O157 illnesses were attributed to two food categories suggesting that interventions for E. coli O157 focusing on these two food categories may be most effective in reducing illnesses. Most
L. monocytogenes illnesses were attributed to three food categories implicated in outbreaks in recent years.


Campylobacter attribution estimates were not provided. This was due to concerns about the limitations of using outbreak data that attributes Campylobacter illnesses to foods that are not routinely consumed by the general public. For example, 90% of dairy outbreaks involved raw milk and 55% of chicken outbreaks involved chicken livers, neither of which are readily consumed by the general public. As such, IFSAC analysts are developing other methods to estimate the sources of Campylobacter infection in future publications.

The authors advise that the estimates provided should not be interpreted as suggesting that all foods in a category are equally likely to transmit pathogens and comparisons over years can be skewed by a limited number of outbreaks. These results should be used with other scientific data for decision making. Overall, the attribution estimates can help inform efforts to prioritize food safety initiatives, interventions, and policies for reducing foodborne illnesses. The estimates also allow stakeholders (i.e. scientists; federal, state, and local policy-makers; the food industry; consumer advocacy groups; and the public) to assess whether prevention-oriented measures are working at intended.

A Look Back at the U.S. Foodborne Outbreaks Occurring in 2023

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This article takes a look back at the foodborne outbreaks that occurred in 2023. Currently, 27 outbreaks have occurred involving Shiga toxin-producing E. coli, Salmonella, Listeria monocytogenes, Hepatitis A, Cyclospora, Cryptosporidium, natural toxins, and lead. This resulted in 1,076 reports of illness from the consumption of 14 known product types and 11 unknown product types. According to public health officials, these numbers are severely underreported. Many illnesses go unrecognized as being linked to a contaminated food. The table below provides a brief overview of the outbreaks reported by FDA, USDA FSIS, and CDC. Highlights are also provided for outbreaks having known product sources.

Foodborne Outbreaks Occurring in 2023

MonthProductPathogenIllness
February Leafy Greens L. monocytogenes19
March Frozen Strawberries Hepatitis A Virus 10
March Not Identified Salmonella Hartford 54
March Raw Flour Salmonella Infantis 14
April Morel Mushroom Natural Toxin 51
May Broccoli Cyclospora cayetanensis 20
May Raw Cookie Dough Salmonella Enteritidis 26
May Ground Beef Salmonella Typhimurium 26
June Pico de Gallo Salmonella Paratyphi B 37
June Not Identified Cyclospora cayetanensis 72
July Not Identified Cyclospora cayetanensis 140
July Not Identified E. coli O157:H7 12
July Not Identified E. coli O26 13
July Not Identified Cyclospora cayetanensis 59
July Ground Beef Salmonella Saintpaul 18
August Ice Cream L. monocytogenes 2
August Not Identified Cryptosporidium 11
August Ground Beef E. coli O157:H7 Not Reported
September Watermelon and Cantaloupe Salmonella Newport 11
October Onions Salmonella Thompson 80
November Not Identified E. coli O121:H19 37
November Apple Cinnamon Puree Elevated Lead Levels 65
November Not Identified E. coli O103 12
November Peaches, Plums, Nectarines L. monocytogenes 11
November Cantaloupe Salmonella Sundsvall & Oranienburg 230
November Not Identified Salmonella Newport 43
December Not Identified L. monocytogenes 3

February – Leafy greens were epidemiologically linked to nineteen illnesses involving L. monocytogenes occurring across 16 states. However, there was not enough data to identify a specific type or producer of the leafy greens.

March – Frozen organic strawberries sourced from farms located in Baja California, Mexico were linked to ten illnesses from hepatitis A virus. This outbreak strain was genetically identical to a previously isolated strain from fresh organic strawberries grown in Baja California, Mexico implicated in an outbreak in 2022.

March – Raw flour contaminated with Salmonella Infantis was linked to an outbreak that caused fourteen illnesses. Seven of the reported ill said they had consumed raw dough or batter prior to symptom onset.
April – Morel mushrooms served raw or lightly cooked at a sushi restaurant in Montana caused fifty one illnesses and two deaths. Left over mushrooms tested were found to be true morels and not false morels that contain the toxin gyromitrin. However, documented cases of similar illness have been reported due to low levels of naturally occurring heat-labile hydrazinic toxins found in the raw morels.
May – Broccoli caused an outbreak resulting in 20 illnesses from Cyclospora cayetanensis, however, likely
due to the short product shelf life, an advisory was never issued.
May – Raw cookie dough sold at a national retailer of take and bake pizzas was linked to an outbreak that caused twenty six illnesses resulting from Salmonella Enteritidis. Fifteen of the ill reported eating raw cookie dough from the retailer a week prior to when they got sick.
May – Ground beef was linked to an outbreak causing twenty six illnesses from Salmonella Typhimurium. Some of the ill people reported eating undercooked ground beef.
June – Pico de Gallo caused an outbreak that was linked to thirty seven illnesses resulting from Salmonella Paratyphi B. An advisory was never issued, likely due to the short shelf life of the product.
July – Ground beef was epidemiologically linked to eighteen illnesses caused by Salmonella Saintpaul. However, there was not enough data to identify a common source of the ground beef.
August – Ice cream contaminated with L. monocytogenes was linked to two cases of listeriosis. Whole genome sequencing (WGS) performed on the strains found in product and several environmental samples taken from the production facility indicated a match to the outbreak strain of L. monocytogenes.
August – Ground beef contaminated with E. coli O157:H7 was suspected to be involved in an outbreak, however a USDA-FSIS public health alert was not issued.
September – Watermelon and cantaloupe caused an outbreak resulting in eleven illnesses from
Salmonella Newport, however an advisory was never issued likely due to the short product shelf life.
October – Diced onions caused an outbreak resulting in eighty illnesses from Salmonella Thompson. Three water and three environmental samples collected from the farm that supplied the contaminated onions tested positive and matched the outbreak strain as determined by WGS.
November – Apple cinnamon fruit puree pouches were recalled after reports of acute lead exposure in multiple children led to an investigation and finding of extremely high concentrations of lead in multiple product lots. Since only products containing cinnamon had elevated lead levels, FDA’s leading hypothesis in the ongoing investigation is that cinnamon used in the recalled pouches is the likely source of contamination.
November – Peaches, plums, nectarines (i.e. stone fruit) were epidemiologically linked to eleven illnesses involving L. monocytogenes. Subsequent sampling and testing of 2lb bagged peaches from the supplier were found positive and linked with WGS to outbreak illnesses occurring as far back as August 2018.
November – Cantaloupe have been linked to the largest outbreak of the year, resulting in 230 illnesses and three deaths from Salmonella Sundsvall & Oranienburg infection. Additionally, 129 illnesses and five deaths reported by Canadian health officials have been linked to this outbreak.

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.

Know Your Suppliers to Protect Your Products

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A Supply-Chain Control Program assures that the ingredients, raw materials, and non-food chemicals you receive are safe and suitable for use. Supplier control is an essential element of a preventive food safety system. The program is built on ingredient specifications that are defined following a hazard analysis, criteria for supplier selection, a process for approving suppliers, development of supplier agreements, and verification activities to assure that the program is in place and effective.

The hazard analysis identifies biological, chemical, physical, and Economically Motivated hazards associated with an ingredient that requires a control to significantly minimize or eliminate the hazard at your facility or at the supplier. It is critical to know what ingredients pose a food safety risk and who will control the identified hazard. If your supplier is controlling the hazard, then you should understand how they are accomplishing this. The food safety hazards presented by the supply chain are related to both the amount of control you have over the sourcing of the ingredient and the amount of transparency that you have with respect to the food safety practices of ingredient suppliers.

Approval of suppliers and ingredients should take place before the ingredient is received in your facility. Supplier Verification activities include audits of the supplier’s facility, reviews of their HACCP or Food Safety Plan, and verification testing of the ingredient at the supplier or upon receipt.

It is important to determine the ability and willingness of a supplier to meet your product specifications. A strong program is based on establishing a formal agreement with your supplier to ensure that they will share in the responsibility for food safety with respect to controlling hazards within their own facility. This may reduce the level of preventive controls needed by you upon receipt of the ingredient.

Your risk is lowest when every ingredient has a written specification detailing microbiological, chemical, and physical requirements as indicated by your hazard assessment and when each lot of ingredient is accompanied by a Certificate of Analysis (COA) reporting the results of appropriate verification testing from a trusted supplier. A robust in-bound receiving program with written procedures for reviewing COAs and documenting shipments with receiving records assures that each shipment meets your specification requirements. Even when other verification activities are in place, testing for hazards controlled by your supplier, at some designated frequency, provides additional evidence that supplier food safety systems are working. Your risk increases when you don’t require a COA for every lot purchased and do not require appropriate verification testing by the supplier or as part of your own receiving program.

Testing upon receipt may seem redundant when the supplier provides a COA. However, independent testing offers not only some assurance of the accuracy of the results reported on the COA, but also assurance that no adulteration of the ingredient has occurred between the time of analysis by the supplier and the time of receipt by the buyer. Verification of the supplier’s testing program as well as your own program should include corroboration that the laboratory performing the analyses is certified to conduct the tests and that methods are accredited and appropriate for testing the ingredients analyzed.

Good management of your suppliers will control microbiological, chemical, physical, Economically Motivated and food fraud hazards. For instance, as part of your Supply Chain Verification program, a review and approval of your supplier’s pathogen and allergen Preventive Control programs will minimize the risk that microbial contaminants and unlabeled allergens will enter your facility. This requires each supplier to have their own written programs. For ingredients you identify as having a particular pathogen concern, close the verification loop with an in-house program that screens statistically representative samples from each lot for the pathogen prior to use – either through a Preshipment Testing program or upon receipt.


The key to an effective Supply Chain Control Program is established policies and procedures and trusted suppliers with whom you are able to partner to prevent product safety issues.

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