Sanitation and customer service strategies implemented during COVID-19 correlated with lower Listeria monocytogenes prevalence in retail delicatessens

The purpose of this study was to evaluate the prevalence of L. monocytogenes and validate a predictive statistical model for assessing L. monocytogenes contamination risk at retail which coincided with the COVID-19 pandemic. Ten environmental samples per store were collected during daily operations two times over 12 months in 44 retail deli departments across seven states. Each sample was tested for L. monocytogenes and other Listeria spp.; confirmation was conducted via whole genome sequencing and PCR amplification of the sigB gene, respectively. A 117-question survey was developed based on previous work in retail deli departments and distributed to store or deli managers once during sampling. Survey questions were correlated with L. monocytogenes using linear regression and ANOVA statistical models. A Firth's bias-corrected logistic regression model was developed to predict the probability of a deli having high L. monocytogenes prevalence (>10%). L. monocytogenes prevalence decreased from 5.8% prior to March 2020 to 4.3% during the pandemic. Squeegees and standing water had the highest L. monocytogenes prevalence of all sampling sites in the study; L. monocytogenes was not found on scales or trash cans. Cleaning and sanitation protocols most highly correlated with L. monocytogenes prevalence. The logistic regression model accurately predicted high L. monocytogenes prevalence in 10/17 stores with high prevalence (α < 0.0001, β = 0.1186) during the COVID-19 pandemic. The COVID-19 pandemic heightened awareness of disease transmission and the importance of sanitation to prevent spread of SARS-CoV-2. This study indicates that there were additional benefits to enhanced sanitation and changes in service practices (i.e., reduced L. monocytogenes prevalence and therefore reduced risk of transmission to foods) beyond decreasing SARS-CoV-2 transmission.