Purpose: The purpose of this study was to assess the efficacy of an aggressive twelve hour deep clean SSOP aimed to reduce persistent LM environmental contamination in retail delis.
Methods: We tested the efficacy of a deep clean SSOP in nine delis in three states. The developed SSOP protocol combined Food Marketing Institute recommended daily SSOPs and input from experts in Listeriacontrol from food manufacturing and sanitation. The SSOP was executed by a trained professional cleaning service during a 12 hour shut-down period. A modified BAM protocol was used to detect LM in 28 food and non-food contact surfaces samples taken immediately before and after each cleaning, and in samples taken monthly for 3 months.
Results: Delis (n = 5) with historically low LM prevalence (<5% samples; >300 samples tested) had no statistically significant changes in LM positive samples after the deep clean. Deep cleans in four delis with historically high LM prevalence (≥10%) had varying efficacy. In two delis, deep cleaning reduced LM positive samples by 50% and 75%; one deli had no change and one store had increased LM positive samples immediately post-deep clean. LM positive samples returned to pre-deep-clean levels in highly prevalent delis based on monthly sampling.
Significance: Deep cleaning delis can be immediately effective in delis with high LM prevalence and persistence and do not increase LM prevalence in stores with historically low LM prevalence. However, a single deep clean may not be sufficient to mitigate LM in some retail delis with evidence of persistence.