Wednesday, February 22, 2023

UKHSA: Worst Norovirus Season In A Decade


Although the winter months are typically the peak season for norovirus infections, over the past few weeks there have been a larger-than-normal number of media reports from around the world on this crazily contagious gastrointestinal malady. 

Mayo Clinic warns about above average rate of Norovirus cases

Multiple regions in China warn public of guarding against norovirus especially on campuses

Noroviruses, which are often mistakenly called `stomach flu’, are single-stranded RNA viruses that are able to evolve rapidly. Victims usually experience nausea, frequent vomiting & diarrhea, and stomach pain – and may also suffer from headache, fever, and body aches. 

The illness generally runs its course in 1 to 3 (very long) days, and most people recover fully. But among those who are aged or infirmed, the virus can take a heavy toll. According to the CDC, in the United States each year the norovirus produces:

The `standard’ mode of norovirus transmission is considered to be the fecal-oral route, but limited airborne transmission is suspected as well. In 2015, in CID Study: Airborne Norovirus In Healthcare Facilities, a study looked for - and found - norovirus in ambient air samples taken from 8 hospitals, both inside and outside of an infected patient’s room.

While the act of vomiting (see Vomiting Larry And His Aerosolized Norovirus) could account for this airborne infusion of the virus, the usual receptacle is a toilet, followed by a power flush (see Nature: Another Toilet Plume Study To Consider) which may also help disperse the virus through the air. 

All of which makes the rapid spread of norovirus the bane of crowded cruise ships, hospital wards, schools and households.  Making matters worse, the alcohol hand sanitizers are largely ineffective against norovirus (see Aye, There’s The Rub).  

In the UK, where norovirus infection is often referred to as the `winter vomiting bug', the UKHSA is reporting the worst norovirus season in a decade, with cases up about 66% above normal (see chart below). 

Yesterday they published:

UK Health Security Agency (UKHSA) data released shows a sharp increase in reports of confirmed cases of norovirus – the most common infectious cause of vomiting and diarrhoea.

UK Health Security Agency
21 February 2023 — See all updates

National surveillance data shows laboratory reports of the virus are 66% higher than the average at this time of year. The biggest increase in laboratory confirmed norovirus has been seen in the group of those aged 65 years and over. While high numbers of cases in this age group is expected at this time of year, these levels haven’t been seen in over a decade.

In response to the increase in cases, UKHSA is reminding the public of the actions that they can take to reduce the spread of norovirus.

Norovirus is highly infectious and is easily spread through contact with someone with the infection or with contaminated surfaces. One of the best ways to prevent the spread of norovirus is by practising good hand hygiene. Most people will make a full recovery within 2 to 3 days but it is important to drink plenty of fluids to prevent dehydration, especially for the very young, elderly or those with weakened immune systems who are more at risk.

The number of outbreaks caused by norovirus have increased in hospitals, schools and care homes, with the majority of outbreaks reported in care home settings.

Dr Lesley Larkin, Surveillance Lead, Gastrointestinal Infections and Food Safety (One Health) Division at UKHSA, said:
Norovirus levels are currently the highest we have seen at this time of year in over a decade. Most reported cases are in the over 65s and we’re also seeing a rise in reported outbreaks, particularly in care home settings.
Please stay at home if you are experiencing norovirus symptoms and do not return to work (particularly if you work with vulnerable people or food) or send sick children to school or nursery until 48 hours after symptoms have cleared. If you have a loved one in a care home or hospital, please avoid visiting until 48 hours after symptoms have cleared.
Regular hand washing is really important to help stop the spread of this bug, but remember, alcohol gels do not kill off norovirus so soap and warm water is best.

NHS Medical Director, Professor Sir Stephen Powis, said:
The number of people in hospitals with norovirus has risen significantly in line with what we are seeing in the community and in care homes – it is a really unpleasant illness to catch, but for the vast majority of people it will usually pass in a couple of days, and self-treating at home is the best way to help yourself and avoid putting others at risk.
How to reduce the spread of norovirus
  • Stay at home if you are experiencing norovirus symptoms. Do not return to work or send children to school until 48 hours after symptoms have cleared. Also avoid visiting elderly or poorly relatives, particularly if they are in hospital or a care home.
  • Wash your hands frequently and thoroughly with soap and warm water but especially after using the toilet or an episode of illness and before eating or preparing food. Alcohol gels don’t kill norovirus.
  • When someone with norovirus vomits, the droplets contaminate the surrounding surfaces. A bleach-based household cleaner or a combination of bleach and water should be used to disinfect potentially contaminated household surfaces and commonly used objects such as toilets, taps, telephones, door handles and kitchen surfaces.
  • If you are ill, avoid cooking and helping prepare meals for others until 48 hours after symptoms have stopped, as norovirus can be spread through food contaminated by the virus when food is handled by symptomatic people or infected individuals.
  • Wash any contaminated clothing or bedding using detergent and at 60°C and, if possible, wear disposable gloves to handle contaminated items. 
You can view the National norovirus and rotavirus surveillance reports: 2022 to 2023 season on GOV.UK.: 2022 to 2023 season on GOV.UK.

According to the UKHSA, so far this year `. . . the majority (77%) of samples characterised were norovirus Genogroup 2 (GII) of which the most frequently identified strain was genotype GII.4 (39%)'. 

While norovirus infection is mostly likely to produce an extremely unpleasant 24-48 hours for a healthy adult, it can be far more serious in young children and the elderly.  Globally, the CDC estimates:

Norovirus is the most common cause of acute gastroenteritis, annually causing an estimated 685 million cases. About 200 million cases are seen among children under 5 years old, leading to an estimated 50,000 child deaths every year, mostly in developing countries.

Regardless of your current age or health, this is virus very much worth avoiding if at all possible.