Deibel Laboratories

Science you can trust from concept to consumer.

outbreak

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

· ·

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 Contaminated Dry Pet Food Causes Outbreak and Nationwide Recall

· ·

An outbreak caused by Salmonella Kiambu has been linked to dry pet food products distributed nationally. Seven cases of illness affecting mainly children aged one year or less have been reported from multiple states since January 2023. Retail product collected for routine testing by the South Carolina State Department of Agriculture was found positive for Salmonella and determined to be closely related to the outbreak strain utilizing whole genome sequencing. This finding led to a nationwide recall of several brands of dry kibble produced at the manufacturing facility with a best by date before 10/31/2024. While outbreaks associated with dry kibble products are infrequent, this new outbreak highlights the challenges associated with dry pet food production and the persistence of Salmonella in low moisture products.

Salmonella is readily found in the ingredients (e.g. rendered animal byproducts and grains) used to make pet food kibble. However, thermal extrusion processes used to make kibble are generally lethal to this organism. Liquid water and/or steam is added to the dry ingredients that are pushed through the barrel of an extruder under intense heat and pressure before exiting through a shaping die. The extrusion process is often validated as a process preventive control to reduce vegetative pathogens by a minimum of 5 logs. Product is then dried resulting in a shelf stable product with a water activity (aw) <0.60.

The low aw prevents pathogen outgrowth but not pathogen persistence if reintroduced after the extrusion step. Product can be re-contaminated from the environment or from the addition of ingredients such as fat and flavorings that are sprayed on the dried kibble to enhance palatability. Post-extrusion contamination likely led to the last major Salmonella outbreak involving kibble that occurred between 2006-2007. During the investigation of this previous outbreak, the same Salmonella serotype was found in the pet food manufacturing environment as well as in two of the 25 brands of pet food produced at the facility. The only positive environmental sample was found in the enrobing/flavoring room where product was coated with a palatant after extrusion. Because the extrusion process utilized time/temperature parameters validated to kill Salmonella, it was thought that cross-contamination of the extruded kibble occurred from contaminated ingredients or environmental contamination during the enrobing/flavoring process.

Supply chain controls can mitigate hazards associated with ingredients added after the extrusion process. Hygiene and sanitation controls can mitigate hazards introduced post extrusion when verified with a robust environmental monitoring program. Pathogen testing should include line samples and environmental samples including air filters, equipment, vents, and drains. Guidance is available from FDA for the safe production of pet food. Deibel Laboratories can provide full service solutions from environmental assessments of facilities to finished product testing for pathogens and indicators as well as validation of nutritional labels for pet foods.

Current Recall a Reminder of Past Incident Involving Frozen Vegetables Contaminated with Listeria monocytogenes

· ·

A new recall of frozen vegetables was published on August 23, 2023, due to the finding of Listeria monocytogenes in sweet cut corn. Recalled products were distributed to major retailers across the U.S. having best by dates as far away as December 2024. Listeria monocytogenes, like many pathogens, will not be eliminated by freezing and will persist in the frozen product. While little information is given in the recall, findings from a 2016 listeriosis outbreak involving frozen vegetables is highlighted in the following.


In 2016, the first multistate outbreak of L. monocytogenes involving frozen vegetables occurred in the U.S. Initially three persons reported illness in 2016, but six more illnesses occurring between 2013 – 2015 were identified using PulseNet traceback data. Two outbreak strains were identified in patients ranging in age from 56 to 91 years and three deaths were reported.


Routine sample of frozen vegetables, and the use of whole genome sequencing (WGS), revealed that eight illnesses were closely related to a strain found in frozen organic white sweet cut corn and one illness to a strain found in frozen organic petite green peas produced by CRF Frozen Foods of Pasco, WA. At the same time, an investigation of the Oregon Potato Company of Pasco, WA found that environmental samples matched the whole genome sequence associated with the eight clinical cases and the CRF frozen organic white sweet cut corn. However, a connection between the companies is unknown because the FDA is prohibited by law from releasing publicly certain information about supply chains, which may constitute confidential commercial information.


A recent publication describes the investigational findings by federal and state regulatory agencies at the two frozen vegetable manufacturers. Observations at the CRF Frozen Foods’ facility indicated that the materials and design of equipment and utensils did not allow proper cleaning and maintenance, and could be potential sources of contamination. An investigation of the facility did not find L. monocytogenes in the environment, but L. innocua was found in zones 1 – 3 which FDA considers evidence of conditions that would be suitable for L. monocytogenes.


Seven L. monocytogenes positive zone 1 swabs, two positive zone 2 swabs, ten positive zone 3 were found in the Oregon Potato Company’s facility. Two of these positives, one zone 1 swab and one zone 3 swab,- matched an outbreak strain also found in CRF’s frozen organic white sweet cut corn. Inspectional observations made include:

  • failure to clean food‐contact surfaces as frequently as necessary to protect against contamination
  • facility construction that did not prevent condensate from contaminating food‐contact surfaces
  • food‐contact surfaces not adequately cleaned and sanitized
  • failure to maintain physical facilities in a sanitary condition
  • facility construction not allowing adequate cleaning of floors and walls

A FDA warning letter was issued and noted the presence of L. monocytogenes in the facility as being indicative of inadequate sanitation efforts to effectively control pathogens in the facility. Although these products are considered not ready‐to‐eat, many consumers may use these products
without proper cooking. Cooking instructions should be clear and validated, and consumers should be informed that consuming undercooked or uncooked frozen vegetables could lead to foodborne illness.

A Recent Soft Serve Ice Cream Outbreak and a Look Back at Past Incidents Involving Pathogen Contamination

· ·

A recent outbreak of listeriosis has been linked to Soft Serve On The Go ice cream cups, resulting in 2 illnesses. An investigation by the Pennsylvania Department of Agriculture detected the presence of Listeria monocytogenes in an unopened sample of ice cream taken from a patient’s home. The product isolate was matched to the clinical L. monocytogenes outbreak strain by whole genome sequencing. Five positive samples of finished product obtained from the production facility by the New York State Department of Agriculture and Markets also matched the outbreak strain.

A recall of products distributed nationally is currently ongoing. However, this is not the first outbreak or recall associated with ice cream and many others have occurred as shown in the tables below.

YearLocationPathogenIllnessesDeathsProducer
2022MultistateL. monocytogenes281Big Olaf Creamery
2014WashingtonL. monocytogenes22Snoqualmie Ice Cream
2010-2015MultistateL. monocytogenes103Blue Bell
2005MultistateSalmonella260Cold Stone Creamery
1994MultistateSalmonellaEstimated 224,0000Schwan’s
Past ice cream outbreaks are shown in the following table.
DatePathogenPathogen SourceProducer
07/13/2022L. monocytogenesEnvironmentBig Olaf Creamery, LLC
06/06/2022SalmonellaPeanut ButterTaharka Brothers Ice Cream
02/12/2022L. monocytogenesEnvironmentThe Royal Ice Cream Company, Inc.
04/27/2021L. monocytogenesNot MentionedVelvet Ice Cream
05/14/2020L. monocytogenesNot MentionedRamar Foods
03/17/2020L. monocytogenesEnvironmentWorking Cow Homemade Ice Cream
Recent ice cream recalls due to pathogen contamination are shown in the following table.

Contamination of ice cream products generally occurs after pasteurization, resulting from sources that include the addition of contaminated inclusions (e.g. fruits, nuts, candy, or bakery pieces) to the finished product, contamination from the production environment, and inadequate sanitation of equipment such as filling heads. Freezing ice cream can prevent pathogen outgrowth, but it will not eliminate pathogen presence. Low levels of pathogens causing illness were identified in the 1994 Schwan’s outbreak (Salmonella 0.004-0.46 MPN/g) and 2015 Blue Bell outbreak (L. monocytogenes 3.9-7.1 MPN/g).

Supplier verification programs are critical to evaluate inclusions and reduce the risk associated with them. Inclusions and flavors must be ready-to-eat and any required Process Preventive Controls must have been applied at the supplier, unless the ice cream manufacturer assumes this responsibility.

Sanitation controls are critical to prevent post pasteurization pathogen contamination of finished ready to-eat ice cream products. This is especially true for L. monocytogenes. Cross contamination with L. monocytogenes from the environment is identified in Blue Bell’s 2015 outbreak and numerous recalls. Ice cream processes can be hard to clean, leaving behind nutrients for microbial growth. Listeria can grow,
form biofilms, and persist in harborage sites such as drains leading to cross contamination. Biofilm formation is a constant problem in ice cream producing facilities and requires proper cleaning and sanitizing procedures for their removal and prevention. The effectiveness of sanitation programs are verified by the results attained from a well-designed environmental monitoring program

The FDA Releases 2022 Cantaloupe Outbreak Investigation Report

· ·

By Ryan Maus

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 following describes FDA’s investigational findings and provides their recommendations to growers of melons and similar produce.

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.