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Norovirus may linger on dishes, utensils in restaurants
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Norovirus appears harder than bacteria to remove from tableware through the standard sanitization processes used in many food service establishments, according to study results published online recently.
Researchers from the department of food science and technology at The Ohio State University evaluated the sanitization efficacies of manual and mechanical protocols for washing all types of tableware and flatware used in restaurants. The investigators studied the survivability and response to the experimental conditions of Escherichia coli K-12 and Listeria innocua compared with murine norovirus 1 (MNV-1).
The findings indicate that the current protocols, which include sanitization with sodium hypochlorite (chlorine) and quaternary ammonium, did not achieve the required 5-log reduction in MNV-1. After washing, a maximum of 3-log reduction in the virus was obtained; tap water served as control.
Tableware and flatware in the study were contaminated with cream cheese and reduced-fat milk inoculated with MNV-1, E. coli K-12 and L. innocua.
“We know that when public food establishments follow the cleaning protocols, they do a very good job at getting rid of bacteria,” study researcher Melvin Pascall, PhD, said in a press release. “Now we can see that the protocols are less effective at removing and killing viruses — and this may help explain why there are still so many illnesses caused by cross-contaminated food.”
Norovirus is the leading cause of epidemic gastroenteritis worldwide and causes at least 50% of all US gastroenteritis outbreaks, according to the CDC.
The investigators plan to study hepatitis A and influenza viruses using the same study design.
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Andi L. Shane, MD, MPH, MSc
Researchers from the department of food science and technology at the Ohio State University evaluated the in vitro inactivation of mechanical and manual tableware washing procedures with chlorine, quaternary ammonium (QAC) sanitizing solutions, or tap water (control). Ceramic plates, drinking glasses, and stainless steel forks were contaminated with cream cheese and fat-free milk containing murine norovirus-1, E. coli K-12, and Listeria inocula to simulate contamination in the presence of food residues. Items were then subjected to mechanical or manual cleansing with chlorine, QAC, or tap water. Viral titers and bacterial titers per item of tableware were compared. Standardized evaluations to simulate procedures in commercial kitchens demonstrated that the use of QAC and sodium hypochlorite were sufficient for sanitization of the test bacterial organisms but not for the murine norovirus. Mechanical dishwashing offered a slight advantage over hand-washing in reduction of organism titer.
The incomplete sanitization of tableware with conventional products combined with a low infectious dose could explain the relationship between norovirus and commercial food preparation activities. Long-term care facilities are the most commonly reported places for norovirus outbreaks in resource endowed settings, along with restaurants, cruise ships, communal dinners, summer camps, and child care centers; all settings where food preparation and service is carried out by multiple handlers in large volumes.
Strategies to reduce norovirus infections include aggressive removal of food residues prior to sanitization, limiting the number of handlers involved in food preparatory activities, and evaluating combinations of sanitizers to maximize efficacy. A revised approach to sanitization may be required to induct food preparation facilities into the "clean plate" club.
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