Norovirus (vomiting bug)

Overview

Norovirus is a very contagious stomach bug that causes vomiting and diarrhoea. Most people recover within a few days without specific treatment. Young children, older adults and people with other illnesses are at higher risk of dehydration. It spreads by direct contact with an infected person, through contaminated food or drink, and through contaminated surfaces.

Symptoms

What a clinician may find

• Vomiting and diarrhoea.
• A high temperature in some people.
• Signs of dehydration, such as dark urine, passing less urine than usual, or fewer wet nappies in babies.

Complications

• Dehydration, from fluid lost through vomiting and diarrhoea.
• More severe or prolonged illness in some people, including older adults and those with weakened immune systems.

Diagnosis

Diagnosis is usually based on the symptoms. Stool test panels can detect norovirus.

Treatment

There is no specific cure or antiviral medicine, and antibiotics do not work because the cause is a virus. Care focuses on rest and drinking plenty of fluids to prevent dehydration. A pharmacist can supply oral rehydration powder when there are signs of dehydration.

Prevention

Washing hands with soap and water is the key measure, because alcohol-based hand gels do not inactivate the virus. UK guidance advises staying away from work, school and hospital or care home visits, and avoiding preparing food for others, until 48 hours after symptoms stop. The CDC says no norovirus vaccine is currently available.

Key facts

What are the symptoms of norovirus?

The NHS says the main symptoms of norovirus usually start suddenly. They are feeling sick, being sick and diarrhoea. The CDC lists nausea, stomach pain, fever, headache and body aches among the symptoms, and says they usually start 12 to 48 hours after exposure.

The CDC says most people get better within one to three days. The NHS says symptoms typically last up to two or three days, and UKHSA says most people recover in two to three days without needing any medicine.

The CDC says frequent vomiting and diarrhoea can cause dehydration, which is most dangerous for young children, older adults and people with other illnesses. NHS pages describe signs such as dark yellow, strong-smelling urine, passing urine less often than usual and feeling dizzy or lightheaded. In babies, the signs include fewer wet nappies than usual. The CDC adds that children may cry with few or no tears.

How does norovirus spread?

The CDC says norovirus spreads mainly by the faecal-oral route, either through direct contact with an infected person or through contaminated food or drink. It can also spread when people touch contaminated surfaces and then put unwashed fingers in their mouths. CDC guidance gives an estimated infectious dose as low as 18 virus particles.

The CDC says people are most contagious while they are ill and in the few days after recovering, and that studies show some people can still spread the virus for two weeks or more after feeling better. UKHSA says people may still be shedding the virus for 48 hours after symptoms stop.

Shellfish such as oysters can carry norovirus when grown in polluted water, and the CDC advises cooking shellfish thoroughly. A CDC analysis found that most foodborne norovirus contamination happens during food preparation.

The CDC says outbreaks often occur where people live or gather closely, including hospitals, nursing homes and other long-term care facilities, cruise ships, camps, dormitories and hotels.

How is norovirus diagnosed and treated?

The CDC Yellow Book says norovirus infection is generally diagnosed from clinical symptoms. It also notes that stool test panels can detect the virus with good sensitivity and specificity.

The NHS says there is no specific medicine for norovirus and that the illness has to run its course. The CDC Yellow Book says antibiotics are not useful, and UKHSA says they do not work because norovirus is a virus. Care centres on resting and drinking plenty of fluids to prevent dehydration.

The NHS advises avoiding fruit juice and fizzy drinks, which can make diarrhoea worse, and says children under 12 should not be given medicine to stop diarrhoea. NHS guidance also says children under 16 should not be given aspirin.

For babies, NHS guidance says breastfeeding or bottle feeding can continue, formula should be made up at its usual strength, and smaller, more frequent feeds may help breastfed babies who are being sick. A pharmacist can recommend oral rehydration powder when there are signs of dehydration, and the CDC says oral rehydration fluids are most helpful for mild dehydration.

When should someone get help for the vomiting bug?

The NHS says to call 999 or go to A&E if vomit contains blood or looks like coffee grounds, or is green. It gives the same advice for a sudden severe headache, a stiff neck with sensitivity to light, severe tummy pain, confusion or difficulty breathing. Dehydration can also lead to shock, and the NHS says to call 999 for signs such as blue, grey, pale or blotchy skin, severe difficulty breathing, confusion or being hard to wake.

The NHS says to call NHS 111 if diarrhoea lasts more than 7 days or vomiting lasts more than 2 days, if fluids cannot be kept down, or if there is blood in the diarrhoea. NHS 111 is also the route for concerns about a baby under 12 months, and for a child under 5 with signs of dehydration such as fewer wet nappies.

UKHSA asks people with symptoms not to go to A&E or a GP surgery unless advised to. Phoning the GP or NHS 111 is the suggested first step, and a pharmacist can advise on oral rehydration.

How can the spread of norovirus be reduced?

The NHS and CDC say washing hands with soap and water is the key measure, and that alcohol hand gels do not kill norovirus. The CDC also advises cleaning and disinfecting contaminated surfaces and washing laundry in hot water. UKHSA advises using bleach-based products on surfaces. NHS guidance says soiled clothes and bedding should be washed separately on the hottest cycle the fabric allows.

UKHSA advises staying at home until 48 hours after symptoms stop, and not preparing food for others during that time. The NHS and UKHSA also ask people who are unwell not to visit hospitals or care homes.

UK outbreak guidance for health and care settings describes keeping affected people apart, frequent cleaning of touched surfaces with chlorine-based products, and closing affected bays, wards or care homes to new admissions where appropriate.

The CDC says no norovirus vaccine or antiviral is currently available and that vaccine development is advancing.

Frequently asked questions