One diner vomited, and norovirus spread table by table across the restaurant
In December 1998 a single guest was sick on a restaurant floor; staff cleaned up and dinner went on. Days later 52 of the 126 diners fell ill. Researchers mapped the seating and found infection rates fell with distance, from over 90 percent at the guest's own table to 25 percent across the room.
Norovirus, once called Norwalk virus after a 1968 outbreak in Norwalk, Ohio, is the leading cause of gastroenteritis. It causes vomiting, watery diarrhoea and stomach pain, typically starting about a day after exposure and clearing within one to three days. Globally it accounts for roughly 685 million cases and 200,000 deaths a year, with children under five the most affected. In the United States it is behind about half of all foodborne outbreaks, and cases cluster in winter.
Its reach comes from how easily it moves. Most reported outbreaks, between 62 and 84 percent, pass directly from person to person, and vomiting can put the virus into the air. At a scout jamboree in the Netherlands each sick person infected about 14 others until hygiene was tightened, and still about two afterwards. People keep shedding virus for weeks after they feel well. Shellfish cooked below 75 degrees Celsius and salad ingredients are the foods most often blamed, and a 2017 outbreak in Quebec that sickened over 700 people was traced to imported frozen raspberries.
Part of the difficulty is structural. The virus has no outer lipid envelope, which is why alcohol hand sanitisers tend to work poorly against it; the source points instead to hand washing and disinfecting surfaces. There is no vaccine and no specific treatment, only supportive care with fluids. Immunity after infection lasts from six months to two years but covers only the same genotype, and the virus mutates quickly even by the standards of RNA viruses.
Most human infections come from two of at least seven genogroups, and one strain family, GII.4, drives the majority of adult outbreaks and periodically sweeps the globe. Laboratory PCR tests are sensitive enough to detect as few as 10 virus particles. Serious illness is rare, but the young, the elderly and people with weak immune systems can be endangered by dehydration.
Source: Norovirus
