A Look at the New Strain of Norovirus

A new strain of norovirus, known as “GII 4 Sydney” since it was first identified in Australia last year, has caused more than 140 outbreaks of stomach illness in the U.S. from the time when it first emerged here in September 2012. According to the Centers for Disease Control and Prevention, GII 4 Sydney is now responsible for at least 60% of the norovirus outbreaks in the U.S.

It’s particularly difficult to control norovirus cross-contamination because the bug resists traditional methods of sanitizing, said Melvin Pascall, PhD, associate professor in the department of food science and technology at Ohio State University. In a study published in PLoS One in December, Dr. Pascall and colleagues contaminated dishware with norovirus, E. coli, and Listeria, and then tried both hand-washing and dishwasher sanitation with the commonly used agents chlorine and quaternary ammonium to remove the bugs.

Both hand-washing and mechanical dishwashing reduced E. coli and Listeria to safe levels, but the norovirus was still going strong. “The structure of the virus makes it very small and very sticky, which means that it is difficult to remove,” said Dr. Pascall.

“Norovirus is highly contagious and it takes only a few viral particles to infect humans,” noted Jianrong Li, PhD, assistant professor of food virology at Ohio State University. “These results would indicate that neither the detergents nor sanitizers used in current cleaning protocols are effective against the norovirus at the currently used concentrations.”

Dr. Pascall and Dr. Li are now investigating several new cleaning agents that may prove more effective at removing norovirus. In the meantime, they caution restaurants, food distributors, and others in the food supply chain to make sure that workers who appear ill take sick leave rather than running the risk of cross-contamination. “Keep sick employees out of the kitchen,” Dr. Pascall urged.

Dr. Pascall also recommended vigilance in dishwashing practices. “If you observe that the automatic dishwasher has not effectively removed old food, get those dishes rewashed and scrubbed,” he said. “If just one or two dishes in a batch come out like that, it’s better to rewash the whole batch because it tells you that the washer is not working at optimum performance.”