Moisture matters: unintended consequences of performing wet sanitation in dry environments

Cross-contamination of low-moisture foods (LMFs) with pathogens from equipment and environmental surfaces during production is a food safety concern. Wet sanitation is sometimes employed to mitigate cross-contamination in LMF facilities, but the introduction of moisture to otherwise dry environments can inadvertently promote microbial growth. This study evaluated the risks associated with wet sanitation in LMF facilities by characterizing evaporation kinetics on powdered infant formula (PIF)-soiled surfaces, monitoring relative humidity (RH) in an LMF facility during and after wet sanitation, and assessing the growth of Salmonella, Listeria monocytogenes, Cronobacter sakazakii, and Enterococcus faecium spot inoculated on PIF-soiled stainless steel coupons under dynamic RH conditions. As expected, higher RH slowed drying of PIF-soiled surfaces, prolonging periods when the soil's water activity (a_w) was high enough to support microbial growth. Correspondingly, all four organisms grew significantly at 81% and 97% RH over 120 h (P < 0.05), while only E. faecium grew significantly below 81% RH (P < 0.05). Monitoring of RH during and after wet sanitation in a commercial facility revealed spikes up to 100% RH during sanitation and sustained RH above 75% for more than 7 h in poorly ventilated areas. When those facility RH conditions were simulated in the laboratory, Salmonella populations on PIF-soiled coupons increased by more than 3.5 log CFU within 66 h. These findings demonstrate the potential for wet sanitation to unintentionally enable environmental pathogen growth and highlight the importance of moisture and RH control in LMF facilities.IMPORTANCEWet sanitation is commonly employed by low-moisture food (LMF) manufacturers for allergen changeovers and to prevent cross-contamination from surfaces, but regulators, manufacturers, and researchers have all expressed concerns that wet sanitation may promote the growth of pathogens in otherwise dry production environments. Despite these concerns, research on the impact of wet sanitation on facility relative humidity (RH) and its influence on microbial proliferation in low-moisture production environments remains limited. This study provides evidence that wet sanitation substantially increases facility RH, leading to persistent hydration of soiled surfaces, creating conditions that enable microbial growth. These findings reinforce concerns over the use of wet sanitation in LMF production. This also demonstrates the need for reducing water use in LMF production facilities, implementing RH control strategies, as well as the adoption of alternative or supplemental dry sanitation strategies to mitigate microbial risks.