Norovirus cases rise by 41 per cent to twice average level

Norovirus cases have risen by more than 40 per cent in a fortnight, fuelled by a new dominant variant, new data indicate.

The number of people testing positive for norovirus in the national laboratory reporting system jumped by 41 per cent in the two weeks to Sunday 20 October, according to figures from the UK Health Security Agency (UKHSA)

This puts laboratory-detected cases at more than twice the average level for this time of year seen in the past five years.

Meanwhile, norovirus outbreaks in hospitals have been 37 per cent higher than the five-year average this season, with 26 outbreaks reported since the season began in July, the figures show.

Although these figures don’t give a precise indication of the number of norovirus infections in the general population, they do give a reasonable sense of the degree to which cases are rising or falling, scientists said.

It is unclear why the virus is quite so high for the time of year, although a UKHSA spokesperson noted that “there has been an increase GII.17 variant since April 2024, and during the first 16 weeks of the 2024-25 season this was the most commonly detected norovirus genotype. The increase of the variant has been observed in other counties and is being closely monitored”.

It is also unclear whether GII.17, which is not new but has only recently gained dominance in the UK, is intrinsically more contagious than the previous most common variant, GII.4.

But research has suggested that immunity built up from being previously infected by GII.4 may not protect as effectively against infection with GII.17 – and this could be a key factor behind soaring cases.

Norovirus is a highly contagious virus that causes gastroenteritis – an inflammation of the stomach and intestines.

It spreads easily through contaminated food, water, surfaces, and direct contact with an infected person.

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Common symptoms include nausea, diarrhoea, and vomiting and in some cases, people suffer additional symptoms such as fever, headaches, and body aches.

“We are heading into the winter season with norovirus levels higher than usual, and we expect norovirus to spread more in the coming weeks,” said Gauri Godbole, deputy director gastrointestinal infections at UKHSA.

“Recently, we’ve seen the biggest rise in cases in adults, especially those aged 65 and over.

Ms Godbole added: “To help reduce the spread of norovirus you can take steps to avoid passing the infection on. If you have diarrhoea and vomiting, do not return to work, school or nursery until 48 hours after your symptoms have stopped and don’t prepare food for others in that time either. If you are unwell, avoid visiting people in hospitals and care homes to prevent passing on the infection in these settings.

“Washing your hands with soap and warm water and using bleach-based products to clean surfaces will also help stop infections from spreading. Alcohol gels do not kill norovirus so don’t rely on these alone.”

Simon Williams, a behavioural scientist and public health expert at Swansea University, added: “Our behaviour is at the core of why noroviruses are spreading and also how to prevent outbreaks and our risk of catching it.”

“Handwashing is an obvious one. It’s one of the main ways to help prevent the spread of norovirus and similar viruses. But it’s surprising how many people don’t necessarily handwash effectively. And although hand hygiene really increased when the pandemic hit, it seems some people have been returning to bad hand hygiene habits,” he added.

Dr Williams points to a study by the Food Standards Agency which found the proportion who reported handwashing with soap and warm water “always” or “most of the time” declined from 79 per cent in April 2020, at the peak of concerns about the pandemic, to 68 per cent in January 2022. And he expects that number to have fallen further since then.

Professor Sheena Cruikshank, of Manchester University, added: “I can’t say for definite why it’s so high this year. However, it’s a virus that can be spread by inhaling aerosols as well as a good ability to survive on surfaces so when we gather together more indoors its better able to spread.

“And we have a lot of poorly ventilated buildings which will not help,” she added.

The data relate to England but scientists say trends in viruses are typically similar across the UK.