Identification and classification of sampling sites for pathogen environmental monitoring programs for Listeria monocytogenes: Results from an expert elicitation.

Pathogen Environmental Monitoring (PEM) programs for Listeria are important to reduce the contamination risk for exposed Ready-To-Eat (RTE) food products with L. monocytogenes. Specific guidance to identify appropriate sampling sites in individual facilities, including equipment and other sites, will facilitate effective L. monocytogenes control and PEM programs. Key goals of Listeria PEM programs are to (i) identify and eliminate niches that allow for Listeria growth and survival and (ii) verify and validate preventive controls such as sanitation programs and sanitation standard operating procedures (SSOPs), sanitary equipment and facility design. Here, an initial list of 77 sampling sites covering Zones 1-4 was assembled based on current literature and guidance documents with initial classification of sites into (i) Zones 1, 2, 3, and 4; (ii) likely niches or transfer sites, and (iii) verification sites or indicator sites. An expert elicitation that included responses from 16 food safety professionals was used to (i) refine sampling site descriptions and identify 6 new sampling sites that were not included in the original list, (ii) refine classification of sites (e.g., into niches versus transfer sites), and (iii) rank sites on level of importance from 1 to 5. The final sample site list includes sampling sites classified by zone and type of site as well as relative importance of site based on reviewer feedback. This document thus provides an initial set of sites that can be used by industry to help in the development or refinement of Listeria PEM programs. The availability of this ranked list of sampling sites should reduce barriers to development of science based Listeria PEM programs.

Enhanced Sanitation Standard Operating Procedures Have Limited Impact on Listeria monocytogenes Prevalence in Retail Delis.

In a recent longitudinal surveillance study in 30 U.S. retail delicatessens, 9.7% of environmental surfaces were positive for Listeria monocytogenes, and we found substantial evidence of persistence. In this study, we aimed to reduce the prevalence and persistence of L. monocytogenes in the retail deli environment by developing and implementing practical and feasible intervention strategies (i.e., sanitation standard operating procedures; SSOPs). These SSOPs were standardized across the 30 delis enrolled in this study. SSOP implementation was verified by systems inherent to each retailer. Each deli also was equipped with ATP monitoring systems to verify effective sanitation. We evaluated intervention strategy efficacy by testing 28 food and nonfood contact surfaces for L. monocytogenes for 6 months in all 30 retail delis. The efficacy of the intervention on the delis compared with preintervention prevalence level was not statistically significant; we found that L. monocytogenes could persist despite implementation of enhanced SSOPs. Systematic and accurate use of ATP monitoring systems varied widely among delis. The findings indicate that intervention strategies in the form of enhanced daily SSOPs were not sufficient to eliminate L. monocytogenes from highly prevalent and persistently contaminated delis and that more aggressive strategies (e.g., deep cleaning or capital investment in redesign or equipment) may be necessary to fully mitigate persistent contamination.

Listeria monocytogenes and Listeria spp. contamination patterns in retail delicatessen establishments in three U.S. states.

Postprocessing contamination in processing plants has historically been a significant source of Listeria monocytogenes in ready-to-eat delicatessen meats, and therefore a major cause of human listeriosis cases and outbreaks. Recent risk assessments suggest that a majority of human listeriosis cases linked to consumption of contaminated deli meats may be due to L. monocytogenes contamination that occurs at the retail level. To better understand the ecology and transmission of Listeria spp. in retail delicatessens, food and nonfood contact surfaces were tested for L. monocytogenes and other Listeria spp. in a longitudinal study conducted in 30 retail delis in three U.S. states. In phase I of the study, seven sponge samples were collected monthly for 3 months in 15 delis (5 delis per state) prior to start of daily operation; in phase II, 28 food contact and nonfood contact sites were sampled in each of 30 delis during daily operation for 6 months. Among the 314 samples collected during phase I, 6.8% were positive for L. monocytogenes. Among 4,503 samples collected during phase II, 9.5% were positive for L. monocytogenes; 9 of 30 delis showed low L. monocytogenes prevalence (<1%) for all surfaces. A total of 245 Listeria spp. isolates, including 184 Listeria innocua, 48 Listeria seeligeri, and 13 Listeria welshimeri were characterized. Pulsed-field gel electrophoresis (PFGE) was used to characterize 446 L. monocytogenes isolates. PFGE showed that for 12 of 30 delis, one or more PFGE types were isolated on at least three separate occasions, providing evidence for persistence of a given L. monocytogenes subtype in the delis. For some delis, PFGE patterns for isolates from nonfood contact surfaces were distinct from patterns for occasional food contact surface isolates, suggesting limited cross-contamination between these sites in some delis. This study provides longitudinal data on L. monocytogenes contamination patterns in retail delis, which should facilitate further development of control strategies in retail delis.