Efficacy of Warewashing Protocols and Selected Sanitizers for Removal of Foodborne Bacteria and Viruses from Contaminated Tableware

Introduction: Epidemiological outbreak data have identified five major risk factors related to foodborne outbreaks in retail food establishments. The U.S. FDA Food Code addresses controls for all five, including science-based controls for contaminated equipment. One limitation of the controls related to contaminated equipment is that they only address how to reduce bacteria on food-contact surfaces and not viral agents. 

Purpose: The purpose of this study was to evaluate the efficacy of selected sanitizers (tap water control, 200 ppm sodium hypochlorite, acidic electrolyzed water [AEW] and neutral electrolyzed water [NEW]) for removal of bacteria (Salmonella Typhimurium, Listeria innocua) and human norovirus surrogates (murine norovirus [MNV], Tulane virus [TV]) from contaminated tableware using established manual and mechanical warewashing protocols.

Methods: Cream cheese was inoculated with L. innocua, S. Typhimurium, MNV, or TV.  The cheese was applied to ceramic plates to simulate a worst-case contamination scenario.   Plates were cleaned using manual (43°C) and mechanical (49°C) warewashing protocols, and sanitized with one of the test sanitizers. After 1 hour of air-drying, plate surfaces were swabbed and surviving bacteria quantified using nonselective and selective agars, while viruses were quantified using viral plaque assays.

Results: Manual and mechanical warewashing procedures produced a > 5 log and < 4 log reduction in S. Typhimurium and L. innocua, respectively.  MNV and TV showed a < 4 log reduction in viral titer after warewashing.  The use of 200 ppm sodium hypochlorite, AEW, or NEW sanitizers only slightly enhanced microbial inactivation when compared to a tap water control. 

Significance: These data suggest that current manual and mechanical warewashing operations are sufficient for removal of bacteria from contaminated tableware, but are not as effective on foodborne viruses.  Since noroviruses are highly infectious, optimizing warewashing procedures to remove these pathogens is a significant public health challenge.