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Norovirus - GPs' questions answered

Mr John Harris, epidemiologist at the Health Protection Agency answers some common GP questions on norovirus

Mr John Harris, epidemiologist at the Health Protection Agency answers some common GP questions on norovirus

How do I distinguish norovirus from other forms of diarrhoea?

Norovirus is characterised by sudden onset of nausea projectile vomiting and explosive diarrhoea. The disease comes on swiftly and often without warning. The disease was historically known as 'winter vomiting disease' due to its seasonality and typical symptoms.

What is the likely course of the clinical illness?

The symptoms of norovirus infection will begin around 12 to 48 hours after becoming infected. They will start with the sudden onset of nausea followed by projectile vomiting and watery diarrhoea. Diarrhoea tends to be short-lived and less severe than with other causes of gastroenteritis. Some people may have other symptoms such as fever, headaches, myalgia, aching limbs, and abdominal cramps.

The illness is self-limiting and the symptoms generally will last for 12 to 60 hours and most people recover rapidly thereafter. However some people (usually the very young or elderly) may become dehydrated and require hospital treatment. It is important to drink plenty of fluids to prevent dehydration.

There is no treatment for norovirus. The only option (apart from rehydration therapy) is to let the disease run its course. Antibiotics are not needed.

Does it vary according to age?

There is no one specific age group at risk of contracting norovirus – it affects people of all ages, though the highest rates are in children. Immunity is short lived (usually just a few months) so previous exposure to norovirus does not give immunity to future infections.

Is post viral malaise more common that with other viruses?

Recovery is usually complete with no evidence of long term sequelae. Most people are fully recovered within 1-2 days of infection.

How long do you remain infectious (exclusion from school)?

Infectivity usually lasts for 48 hours after symptoms have resolved. Some patients such as immunocompromised may continue to be infectious for many weeks.

Infants at nursery or pre-school groups and those involved in food preparation or clinical and social care staff who have direct contact with highly susceptible patients should be excluded for 48 hours after symptoms have disappeared.

Other people present minimal risk of spreading disease and may return to school or work when their symptoms have resolved and their stools have returned to a normal consistency.

One of the ways to protect against the infection or to help prevent yourself or others becoming infected is by practising good hygiene. This includes thorough hand washing especially after using the toilet and any contaminated surface should be thoroughly disinfected after an episode of illness.

Does the virus frequently mutate so people cannot persist in immunity?

Immunity to norovirus last only about 6 months. In addition, immunity is at least partly strain-specific. Noroviruses are antigenically diverse, and new strains continually emerge. In any year there are a number of strains circulating in the community so you could be infected with one strain and recover and still be susceptible to infection with a different strain.

Is it particularly resilient to normal cleaning methods both of hands and furnishings?

Hand washing should be carried out using soap and water. Alcohol gels are not effective against norovirus.

Hard surfaces should be cleaned with a detergent and hot water to remove deposits and then disinfected with a dilute hypochlorite solution. Care should be taken to follow manufacturer's instructions and protective clothing (gloves) should be worn. It is not recommended for hypochlorite solution to be used on carpets or soft furnishing.

Any furniture or soft surfaces which could have been exposed should be cleaned with hot water and detergent and if possible steam cleaned. If covers can be removed they should be laundered at 70 degrees Celsius.

If practical, carpets should be steam cleaned if they are heat tolerant. If floor covering is heat sensitive or bonded to the backing material with glue, or steam cleaning is not practical, then they should be cleaned with a carpet shampoo. It is not recommended that vacuum cleaning is carried out on contaminated areas as this may risk spreading the virus around.

Any food which may have been exposed should be discarded.

Should we have toys and books in the waiting room?

Fomites can settle on any surface and it is about balancing risks. Books and magazines can easily be wiped clean. It may be best to have toys in the waiting room that can be easily cleaned if they are contaminated.

What is the most common mistake GPs make in the management of this virus?

The majority of those infected will be unlikely to come to the surgery as the illness comes on quite suddenly and it is normally over in one or two days. Those who do visit the GP could potentially infect other patients.

If symptoms are prolonged for more than a couple of days and a GP has any doubts as to the cause of the symptoms then it is advisable to take stool samples to exclude other potential causes with similar presentation such as Salmonella or Campylobacter

All patients, and especially the elderly and the young, should be encouraged to drink plenty of fluids to keep hydrated.

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