Norovirus, often dubbed the 'winter vomiting bug', is a family of viruses responsible for a significant global health burden, infecting an estimated 684 million people every year. This highly contagious pathogen causes acute gastroenteritis, leading to severe bouts of vomiting and diarrhoea.
How Norovirus Spreads and Why It's So Contagious
The virus is notoriously easy to catch. It primarily spreads via the faecal-oral route, where microscopic particles from an infected person's saliva or stool contaminate hands, food, or surfaces before entering another person's mouth. Dr Laraine Washer, an infection prevention expert at the University of Michigan, notes that the infectious dose is astonishingly low: fewer than 20 virus particles can cause illness. In comparison, Covid-19 typically requires 100-400 particles.
Viral particles can survive on hard surfaces like doorknobs for up to two weeks. Transmission can also occur through aerosolised particles when someone is actively vomiting. People become contagious about two days before symptoms appear and can remain so for days or weeks after recovery.
Close-contact settings are high-risk zones. Elderly care facilities, daycares, and airports are common hotspots. Cruise ships are particularly notorious; the US Centers for Disease Control and Prevention (CDC) reported 16 norovirus outbreaks on ships docking at US ports in 2025 alone.
Recognising Symptoms and Knowing When to Seek Help
Symptoms strike suddenly and can be intensely unpleasant. They typically include abdominal cramping, nausea, profuse vomiting, and watery diarrhoea, often accompanied by chills, sweating, and fatigue. Most cases are medically classified as mild, resolving within 72 hours, but the experience is far from trivial, often leaving individuals completely debilitated.
While most healthy adults and older children recover at home, the virus poses a serious threat to vulnerable groups. In the US, norovirus causes 570 to 800 deaths and 70,000 hospitalisations annually. Those at greatest risk are young children under five, adults over 65, and the immunocompromised.
Dr Ambreen Allana, an infectious disease physician, warns that severe dehydration from fluid loss is a major danger, potentially leading to kidney injury in older adults. She advises seeking medical care or visiting A&E for intravenous fluids if high-risk individuals cannot keep liquids down.
For home care, the priority is hydration. Dr Allana suggests matching fluid intake with output, using oral rehydration solutions, ice chips, or anything that can be tolerated. Anti-nausea medication may help, but anti-diarrhoeal drugs like Imodium should be avoided, as they can trap the virus in the gut and prolong the illness.
Prevention is Key: How to Avoid and Contain Norovirus
There is currently no vaccine for norovirus. Dr Andrea Love, an immunologist, explains that the virus's many strains and frequent mutations make vaccine development challenging. Therefore, prevention relies on rigorous hygiene and cleaning practices.
Thorough handwashing with soap and water for at least 20 seconds is the single most important defence. The CDC emphasises that alcohol-based hand sanitisers are ineffective against norovirus and are not a substitute for proper washing.
Cleaning contaminated surfaces requires specific agents. A diluted bleach solution (one cup per gallon of water) or undiluted 3% hydrogen peroxide is needed to kill the virus. Most common disinfectant wipes are insufficient. When laundering soiled items, use a hot wash (above 70°C/158°F) with bleach if possible.
During an outbreak in a household, if possible, designate a separate bathroom for the sick person. When travelling, use a paper towel to touch bathroom taps and door handles. Be cautious at communal dining events like buffets, as they present a high transmission risk.
Finally, do not assume past infection grants lasting immunity. People can be reinfected every few months, making consistent preventive measures essential year-round.
