Purpose: This study was conducted to identify environmental and temporal factors associated with L. monocytogenes and Listeria spp. isolation from produce production environments following rain and irrigation events.
Methods: Two spinach fields, one with a high and one with a low expected risk for L. monocytogenes isolation, were sampled 24, 48, 72 and 144-196 h following irrigation and rain events. Expected field risk was a function of a field’s proximity to water and roads. Environmental and temporal factors were evaluated for their association with L. monocytogenes and Listeria spp. isolation using a generalized linear mixed model. Differences in allelic type diversity between samples were calculated using the Shannon-Weiner Index and T-Hutcheson tests.
Results: The risk for L. monocytogenes and Listeria spp. isolation from soil samples was highest during the 24 h immediately following irrigation and rain events (OR = 23.4 and OR = 7.59, respectively). Additionally, L. monocytogenes and Listeria spp.-positive isolates associated with irrigation events were significantly less diverse than those associated with precipitation events (P = < 0.001), suggesting that irrigation water may be a point source for L. monocytogenes and Listeria spp. contamination.
Significance: These findings suggest that small changes in management practices, such as treating irrigation water or waiting 24 h after rain or irrigation events to harvest crops, may reduce the risk of L. monocytogenes of fresh produce.