Assessing microbial contamination on produce and farm worker hands throughout the production process on farms and packing sheds in northern Mexico

Introduction: Although produce associated outbreaks are a serious public health burden, few studies have characterized contamination routes or points in the production process where contamination has occurred. Thus, we aim to: 1) quantify contamination by fecal indicators on produce and farm workers' hands at different points in the chain of events surrounding the production and post-harvest handling process, and 2) assess the association of microbial levels between matched produce and hand rinse samples. Methods: Produce rinses (160 cantaloupe, jalapeņo, and tomato samples) and matched farm worker hand rinses (107) were collected from 9 farms in northern Mexico at four points: before and after harvest, at the point of distribution from the field, and at the packing shed. Generic E. coli, Enterococci, fecal coliforms, and coliphage were enumerated. Results: Logistic regression found that the risk of E.coli presence on produce was 7 times greater when the matched handrinse had E.coli, (OR=7.1, 95% CI=2.3-21.6), and a significant increased risk was also seen with coliphage (OR=95.6, 95% CI=8.5-1076.4). Spearman's correlations indicated that the concentrations of E. coli (rho=0.9), Enterococci (rho=0.5), and coliphage (rho=0.7) were significantly correlated between hands and produce. Chi-square tests revealed that the prevalence of contamination on produce varied significantly across points in the chain for E. coli (χ2=21.9, p<0.001), Enterococci (χ2=23.5, p<0.001), and coliphage (χ2 =14.5, p=0.002). The prevalence of E. coli on produce increased from 28% before harvest to 67% at the packing shed, Enterococci increased from 69% to 90%, and coliphage from 38% to 61%. Discussion: Hand hygiene and the packing shed environment should be targeted for effective interventions to mitigate the risk of microbial hazards on produce.