Predictive risk models combined with employee- and management-implemented SSOPs identified and reduced Listeria monocytogenes prevalence in retail delis

Abstract

Ready-to-eat (RTE) deli meats sliced at retail are predicted to cause 83% of deli meat-associated listeriosis cases annually. While Listeria monocytogenes is commonly found in delis, environmental prevalence varies by store (0–40%). A deep clean sanitation standard operating procedure (SSOP) executed by a third-party cleaning service immediately reduced L. monocytogenes prevalence in delis, but reductions were not sustained over time. The purpose of this study was to assess the efficacy of a L. monocytogenes predictive risk model and a subsequent deep-clean SSOP (deep clean) conducted by store employees and management complemented with training and facilities improvements all aimed to reduce L. monocytogenes prevalence in stores with known high L. monocytogenes prevalence and evidence of persistence. Fifty delis among six states were screened using a predictive logistic regression model that estimates the probability of high L. monocytogenes prevalence in a deli. The model identified 13 stores with potentially high L. monocytogenes prevalence; seven stores were confirmed and enrolled for further study. Retail employees executed deep clean; additional interventions (e.g., facilities improvements, training) were incorporated in stores. Environmental samples (n = 20) were collected immediately before and after, and for six months post-deep clean. Deep cleans immediately reduced L. monocytogenes prevalence in six of seven stores tested. A total of 21/138 (15.2%) samples before and 8/139 (5.8%) samples after deep-cleaning were positive for L. monocytogenes, with a marginal 16.0% decrease on non-food-contact surfaces (NFCS) immediately after deep clean (p = 0.0309, αadj = 0.0125) and a marginal 10.8% on NFCS during follow-up (p = 0.0337, αadj = 0.0125). Employee executed deep cleans with training, education, and maintenance programs can reduce environmental L. monocytogenes prevalence in retail delis, a pivotal part of preventing subsequent cross-contamination to RTE deli meats.