Highlights:

  • CDC investigating a multistate outbreak of Listeria monocytogenes linked to cooked diced chicken meat
  • The unique facts on L. monocytogenes around temperature, growth conditions, lethality, high-risk populations, mortality rates, and monitoring
  • Government oversight continues to evolve with the release of a new guidance document


Recent Listeria Outbreak

As of September 2019, an outbreak of L. monocytogenes food-borne illness is currently affecting patients in Canada. As of  August 18th, 2019, there have been 7 confirmed cases of L. monocytogenes illness in three provinces: British Columbia (1), Manitoba (1) and Ontario (5). Individuals became sick between November 2017 and June 2019, with six of the seven patients requiring hospitalization. Their ages range from 51 to 97 years, with 86% of patients listed as female.

This current outbreak coincides with an increase in L. monocytogenes illnesses as reported in June 2019. Officials used whole-genome sequencing (WGS) to identify two illnesses which occurred in November 2017 that had the same genetic strain as illnesses which occurred in April and June 2019. A Canadian cooked chicken producer was initially identified as a likely source of this outbreak. The product was supplied to hotel, restaurant, and institutional foodservice establishments, but not for retail sale. On August 18, 2019, the Canadian Food Inspection Agency (CFIA) issued a recall for the producer’s cooked diced chicken meat, and on August 19, the recall was expanded to include natural proportion cooked diced chicken meat distributed by two other distributors.

In addition, the CDC in conjunction with several states and other federal partners are investigating a multistate outbreak of L. monocytogenes infections. Neither a specific food item nor a business associated with its sale or distribution has been identified as the source of the infections in the U.S., but the investigation is ongoing. So far 24 people that are located in 13 states (from Oregon and California to New York and Florida) have been infected with the outbreak strain of L. monocytogenes. Twenty-two known hospitalizations have resulted with 2 reported deaths.

Investigators are using PulseNet, a network of laboratories using WGS to identify related strains of pathogenic bacteria. L. monocytogenes specimens collected from patients occurred from July 20, 2017, to August 1, 2019. The affected patients have ranged in age from 35 to 92, with a median age of 72. 63% percent of ill persons are female. The strain associated with this U.S. outbreak has been shown to be “closely related genetically” to the L. mono cases found in Canada.

The Facts on Listeria

The food industry has been doing battle with L. monocytogenes since the ’80s. Below are some known facts about L. monocytogenes.

  • Temperature: L. monocytogenes is unique with respect to food handling since it can grow at refrigerator temperatures (4°C to 10°C). Freezing also has little detrimental effect on the microbe.
  • Growth Conditions: L. monocytogenes can grow under both anaerobic and aerobic conditions, found in moist environments, soil, decaying vegetation, and water and may be part of the fecal flora of many mammals, including healthy human adults.
  • Lethality: Although pasteurization is sufficient to kill L. monocytogenes, lethality steps require careful validation to ensure complete efficacy. Transfer of the bacterium from the general environment to the food facility production environment and then onto food products can occur. L. monocytogenes is in fact considered an environmental pathogen because it can survive and multiply in a food processing facility. Ready to eat(RTE) food can be contaminated after a pathogen lethality step (cooking or other antimicrobial process) by the addition of contaminated ingredients or through contact with contaminated workers, equipment, packaging materials, dust, moisture droplets, or other contaminated surfaces or fomites. Products that allow the growth of L. monocytogenes to high levels before consumption are at especially high risk due to their exposure to higher levels of this pathogen making illness more likely for susceptible individuals.
  • High-Risk Populations: Persons who have the greatest risk of experiencing severe morbidity and mortality listeriosis are pregnant women and their fetuses, the elderly, and persons with weakened immune systems. Although infected pregnant women may experience only mild, flu-like symptoms, their infections can lead to premature delivery, infection of the newborn or even stillbirth.
  • Mortality Rates: Listeriosis is characterized by a relatively high mortality rate compared to illnesses caused by most other foodborne pathogens (about 20% compared to <1 % for Salmonella or E. coli O157). This continues to be the case as was recently confirmed with the release of FoodNet’s (the Food-borne Disease Active Surveillance Network) preliminary 2018 data which showed that while the incidence of listeriosis cases, defined as the isolation of L. monocytogenes or detection of its nucleic acid sequences from a normally sterile site or from placental or fetal tissue in cases of miscarriage or stillbirth, was low (0.3%) it had the highest rate of hospitalizations (96%) and deaths (21%). In comparison Salmonella and Shiga toxin-producing E. coli had 27/0.4% and 22/0.4%, respectively.
  • Monitoring: FoodNet monitors cases of laboratory-diagnosed infection caused by eight pathogens commonly transmitted through food in 10 U.S. sites. In South Africa, a progressive increase in listeriosis cases starting in mid-June 2017, signaled the beginning of the world’s largest listeriosis outbreak to date. A total of 1,060 cases were reported from January 1, 2017 to July 17, 2018 with 216 (20%) fatalities. Whole genome sequencing (WGS) and epidemiological data were used to identify the source of the outbreak as RTE processed meat manufactured.

Government Oversight

L. monocytogenes continues to be a concern for food regulatory agencies and is an important focus and driver of environmental monitoring programs. In January 2017 the FDA released an updated version of their draft guidance “Control of Listeria monocytogenes in Ready-to-Eat Foods“. This document focuses on prevention, as dictated by the Food Safety Modernization Act (FSMA), including the use of environmental monitoring programs. The goals of these programs should be to:

  1. Verify the effectiveness of a control program for L. monocytogenes
  2. Find L. monocytogenes and harborage sites
  3. Ensure that corrective actions have eliminated L. monocytogenes and harborage sites

This document also provides “test and hold” guidelines when a food contact surface is found to be positive for L. monocytogenes.  FDA Guidance recommends that facilities collect environmental samples from specific food contact sites (FCS) on the production lines at least once every week when the plant is in operation, and test each FCS in the plant at least once each month.

The USDA requires control of L. monocytogenes in RTE meat and poultry products that are exposed to the process environment after undergoing a lethality treatment. Depending on the control method selected, testing of food contact surfaces in the post-lethality processing environment to ensure that they are sanitary and free of L. monocytogenes (or an indicator organism) may be required. An RTE product is considered adulterated if it contains L. monocytogenes, or if it comes into direct contact with a food contact surface that is contaminated with L. monocytogenes. Establishments are recommended not to release product that has been in contact with L. monocytogenes contaminated surfaces without reprocessing the product and verifying that the product is safe.

Retail for meat and poultry has shared jurisdiction with the FDA, state, local authorities, and FSIS. FSIS has developed a Best Practices Guidance document for “Controlling Listeria monocytogenes in Retail Delicatessens” which provides specific recommendations for actions that retailers can take in deli areas to control Listeria contamination of RTE meat and poultry products. It also includes a Deli Self-Assessment Tool that can be used to determine whether the appropriate procedures to control L. monocytogenes have been adopted.

Contact our experts to ensure your Listeria control program is up to the task.

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