Ready-to-eat (RTE) food safety recalls and outbreaks due to product contamination of Listeria monocytogenes from the environment are devastating to affected consumers and their families, the originating food plants, and the food industry. RTE food plants must develop a risk-based environmental monitoring program (EMP) that covers the eight “W”s: why, who, which, where, when, what, what if, and what’s going on.
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The goals of an EMP are to verify the effectiveness of Listeria control and to seek and destroy the pathogen and harborage sites (if present) for regulatory compliance (e.g. FDA Food Safety Modernization Act), recall prevention, audit readiness (e.g. Global Food Safety Initiative), brand protection, and customer and consumer satisfaction.
Although the food safety team develops and implements an EMP, successful implementation relies on the senior management team. This team commits to nurture food safety culture so the EMP is not the flavor of the month to pass an audit.
Listeria spp. is the most suitable indicator and includes psychrotrophic Listeria monocytogenes with relatively low infective dose to cause listeriosis but with relatively high mortality rate in high-risk populations (e.g. young, old, pregnant woman, and immunocompromised patients). For low water activity foods, Enterobacteriaceae and Salmonella spp. are the target indicators.
A master list is required to document Zone 1 food contact surfaces (FCS), Zone 2 non-food contact surfaces (NFCS) in close proximity to FCS, Zone 3 more remote NFCS that are in or near the processing areas and could lead to contamination of Zones 1 and 2, and Zone 4 NFCS in remote areas outside of the processing area from which environmental pathogens can be introduced into the processing environment.
During routine sampling, it is recommended to sample and test at least 10 FCS and 10 NFCS per RTE line in a larger food plant. Within a defined period of time, all sites in the master list are sampled and tested.
Samples should be taken several hours into production (e.g. three to four hours) or preferably just prior to cleanup, which allows time for L. monocytogenes (if present) in harborage sites to contaminate the sampling sites. Frequency should be based on risk, regulation, and industry best practices. According to FDA’s draft guidance for “Control of Listeria monocytogenes in RTE Foods,” higher risk products do not receive a listericidal treatment to adequately reduce L. monocytogenes, are not formulated to prevent the growth of L. monocytogenes or be lethal to L. monocytogenes, and are handled extensively after the pathogen reduction step and prior to packaging. They also do not receive a listericidal control measure in the package, support the growth of L. monocytogenes under normal storage conditions, and have a relatively longer refrigerated shelf life. During routine sampling, high-risk RTE lines should be tested weekly on a random production day. Low-risk RTE lines can be tested at a lower frequency.
An approved sampling and testing method with proper application should be followed by an accredited laboratory (e.g. the FDA’s 2015 “Testing Methodology for Listeria species or L. monocytogenes in Environmental Samples”). A 1 foot x 1 foot area should be sampled if applicable. Proper neutralizing buffer (e.g. D/E neutralizing broth) should be used to neutralize residual sanitizer on the sponge, if applicable, to prevent false negative results.
A finding of Listeria spp. in the RTE processing environment should trigger corrective actions such as intensified cleaning and sanitizing, intensified sampling and testing, comprehensive investigation and root cause analysis, “hold and test” procedures, and preventative measures. Corrective actions should be risk-based (e.g. NFCS versus FCS, low- versus high-risk line, routine versus intensified sampling phase, and isolated versus persistent findings) in reference to regulatory policy and industry best practices. Advances in molecular technology tools (e.g. ribotyping and whole genome sequencing) facilitate definitive root cause analysis.
What’s Going On
Trend analysis is conducted to review the past, take actions today, and improve the future. Trend analysis is conducted to verify Listeria control via time and/or spatial patterns by observing if Listeria findings are increasing in particular sites or areas, increasing in the same area on multiple but non-consecutive sampling occasions, increasing in overall percentage, and/or moving from NFCS to FCS. Statistical methods (e.g. Pareto analysis) should be applied in trend analysis and root cause analysis. Management review should be performed regularly to assess the prevalence of Listeria spp., identify their fluctuations over time (especially at sites with sporadic positives that may have gone unnoticed previously), detect trends, and verify corrective actions.