Components in a Pathogen Environmental Monitoring Program

While there are many similarities in the risk evaluations for Salmonella and L. monocytogenes, there are a few key differences. One is L. monocytogenes can grow slowly at refrigeration temperatures, while Salmonella cannot. Another key difference is L. monocytogenes typically needs to grow to high numbers to cause infection, even in immunocompromised individuals. Salmonella can cause illness at relatively low numbers and often causes illness in otherwise healthy individuals. In general terms, L. monocytogenes has the greatest risk in ready-to-eat (RTE) perishable refrigerated products that allow the growth of this organism and have relatively long shelf lives (e. g., certain soft cheeses, salads, cooked seafood, fresh-cut produce, deli meats, and hot dogs). Alternatively a Salmonella PEMP has the greatest value in facilities manufacturing dry shelf-stable RTE products (e.g., nuts, nut butters, soy products, dry pet food, breakfast cereals, snacks, chocolate). Salmonellosis has also been linked to raw unpasteurized products such as meat, poultry, eggs, dairy, grains, spices, and produce. However, these product contamination events were caused by the inherent presence of the pathogen in the raw products, and not by contamination originating from food manufacturing facilities. A Salmonella PEMP is typically not necessary in facilities manufacturing these types of non-RTE products.

Under some circumstances, for example in dry grain processing facilities that lack a processing step to ensure the elimination of pathogens in the final product and for which the product is not intended for RTE applications, “for cause” pathogen environmental monitoring may be conducted. In these cases routine monitoring is not conducted, but “for cause” monitoring is triggered by the occurrence of an unanticipated event involving the ingress of water into a normally dry processing environment. Water could allow for the potential multiplication of pathogens in the plant environment and a possible increased presence of a pathogen in the finished product. A “for cause” PEMP would be appropriate to evaluate this heightened food safety risk but once the situation returned to a normal operating condition the need for ongoing sampling and testing would be unnecessary.

When the risk evaluation indicates a PEMP is necessary, the next component to consider is to determine the degree of stringency of the plan. Every product, process, and facility is different. The stringency of the plan is based on many factors, such as the historical linkage of the product type with illnesses (for Salmonella, often termed “Salmonella-sensitive ingredients or products). Another important factor is the degree of product exposure to the plant environment. Products exposed to the environment are those having a reasonable likelihood of becoming contaminated if the pathogen of concern exists in areas near product contact surfaces or in other places between the kill step and final product packaging. If product is conveyed in fully enclosed piping into the final container with little to no likelihood of contamination or “hot filled” under controlled conditions, the product would not be considered to be exposed to the plant environment. If the final kill step occurs after product is sealed in the final bacteria-impervious package, the product would also be considered to not be exposed. Other considerations include the history of pathogen findings in the facility, the amount of handling following the pathogen reduction step, the complexity and sanitary design of the equipment, packaging type, distribution conditions, shelf life, intended use of the product, and susceptibility of the targeted consumer. These factors will inform the facility personnel in developing the next component of the program, the sampling plan.

A Sampling Plan

Each facility and product type should have a science-based sampling plan for any PEMP deemed necessary based on the risk evaluation. Critical components of the sampling plan include the determination of the number of samples to collect in each sampled room, area or zone, how often sampling will be conducted (daily, weekly, monthly, etc.), which days of the week, and at what time during the shift samples will be taken. Sampling sites should not be entirely random but should instead target the most likely sites to harbor the organism of concern. Listeria growth niches can occur on product contact surfaces, so these surfaces should be included in the Listeria PEMP sampling plan. Difficult-to-clean sites in product contact areas and close to product contact areas should be heavily targeted. Also, the sampling focus should be on the environment in the most critical area of the plant (the area between the kill step and final packaging). Areas historically associated with Listeria growth niches (e. g., hollow rollers on conveyors, gasket material around doors, hollow support structures, grease inside bearings, slicers, dicers) should be preferentially included in the plan.