One scrap of norovirus is all it takes to infect

If you think SARS-CoV-2 is infectious, consider our old foe, norovirus. Research shows that imbibing just one of these beyond-tiny entities – a mere scrap of RNA – carries a 50 per cent chance that you will have to catapult out of bed several times in the night to worship the toilet bowl. A day or two on dry toast, sipping ginger ale, and most people are back to normal, perhaps a kilo lighter. So they don’t bother reporting it, and they certainly don’t want to tell the friends who hosted dinner.

We suspect that norovirus is our most common cause of foodborne illness (more than 40 per cent), and is vastly underreported because it doesn’t last as long as campylobacter or salmonella, which make you very sick for a week or more.

In the United Kingdom, it’s estimated that for every reported case of gastrointestinal infection, nearly 300 are unreported. In New Zealand, there are more than 6000 reported norovirus cases every year, although it is not a notifiable disease unless there is an outbreak. You can do the arithmetic. That’s a lot of lost work and study days, and a big hit to the economy over time.

Norovirus is a scourge in places where the young, elderly, and immunocompromised are at close quarters – hospitals, rest homes, cruise ships, and childcare centres. It is extraordinarily contagious and requires top to bottom disinfection of surfaces and isolation of infected people. Children can be superspreaders.

Coronaviruses have evolved to invade our respiratory tract, but noroviruses take the digestive route, and can withstand the strong acids in our stomachs. And while coronaviruses are short-lived outside their human or animal host (up to three days) and dislike warm temperatures, the hardy norovirus can survive for a long time (up to 41 days) in the environment, in and on food and surfaces such as keyboards and stainless-steel benches. How often do you eat your lunch at the laptop, and how often do you clean your keyboard?

Transmission of norovirus is by the faecal/oral route, which almost always means that someone at the source of an outbreak has not washed their hands properly after going to the toilet, or that food and water have become contaminated with faecal matter. Perhaps we will see a decrease in cases with everyone paying more attention to hygiene now, and keeping their distance during lockdown periods.

Cooking food thoroughly at 90 degrees Celsius minimum, for at least 90 seconds, will reliably inactivate noroviruses. For raw foods such as fresh produce and seafood it is critical that clean water is used for production and processing, and that food handlers, either in the orchard, processing environment or restaurant, exercise scrupulous hand hygiene.

Hand sanitisers are not as effective as washing hands with soap and water for the removal and/or inactivation of norovirus.

Bottom line: Wash and thoroughly dry your hands after going to the loo and before preparing food. And if you are sick with any sort of stomach upset, stay out of the kitchen.

We suspect that norovirus is our most common cause of foodborne illness.