Purpose: This study developed and tested the efficacy of a model to identify retail delis with high levels of environmental LM contamination from a limited number of samples.
Methods: Forward-stepwise selection constructed a Firth’s bias-corrected logistic regression model using sites from a longitudinal retail deli study (n = 30 stores, 6 months, 4508 samples). Since not all delis have floor drains yet, floor drain and drain-associated sites (e.g., floor adjacent drain) were the largest predictors (OR = 243; CI95= 32, >999) in the model, a second model was constructed excluding drain-associated sites. Models were externally validated using data from the second 6-month sampling period (n = 30 stores, 4495 samples); then used to screen 50 additional delis for evidence of high LM prevalence.
Results: External validation of model A–floor drain included—successfully predicted high prevalence LM contamination in 166/180 events (α = 0.056, β = 0.022). External validation of model B–drain-associated sites excluded—successfully predicted high prevalence LM contamination in 165/180 events (α = 0.050, β = 0.033). We tested the models in 50 delis among 6 states. Collectively the models identified 13 of 50 delis with previously unknown LM contamination history to have increased risk for high LM prevalence; 7 stores were confirmed highly prevalent with evidence of persistence through LM environmental testing (≥2 of 20 food and non-food contact surfaces LM positive ≥2 months).
Significance: The developed screening models are conservative and potentially useful for retailer resource focusing efforts, but not recommend for use in a regulatory capacity due to the considerable false-positive identification rate.