Norovirus

Norovirus is the most common cause of epidemic gastroenteritis worldwide. In the UK, norovirus outbreak is usually seen in the winter months.

Norovirus is a small non-enveloped RNA virus of the caliciviridae family.

It has ten genogroups, but I, II and IV are primarily implicated in human infection. Genogroup II is most common in the UK. Genogroups have a preference for the blood groups; for example, genogroup I has a preference for A and O, while II prefers A and B.

Norovirus is transmitted from human to human by contact, faeco-oral route, fomite and airborne droplets.

Foodborne outbreaks have been associated with green leafy vegetables, fruits, sandwiches, salads and shellfish.

The infective dose of this virus is very low – only about 100 viruses are required to infect an individual.

Norovirus has an incubation period of approx 1 to 2 days.

The most typical symptom of norovirus infection is vomiting, which is often projectile. It also causes diarrhoea, abdominal pain, malaise, myalgia, headache and fever. The symptoms usually last about 2 to 3 days. Reinfection is also known to occur.

Norovirus may precipitate reversible malabsorption, which may last two weeks or more.

Symptomatic individuals may shed the virus in stool for weeks, on average, four weeks. However, maximum shedding occurs usually 24-48 hours after the onset of symptoms.

Some patient groups are at a higher risk of developing severe disease, for example, immunocompromised, elderly and infants. Chronic diarrhoea may occur in immunocompromised patients. Seizure has been reported from children’s, and they also may shed the virus longer, even if asymptomatic.

Norovirus may cause a mild increase in the white cell count. Relative lymphopenia can be seen.

Laboratory diagnosis of norovirus is made mainly by PCR. Asymptomatic shedding of the virus is known to occur; hence the result should be correlated with clinical and epidemiological pictures.

Norovirus infection is mostly self-limiting. Supportive treatment with fluids and nutrition is sufficient. Infection control measures should be implemented to prevent the spread of disease.

All symptomatic patients should be isolated, preferably in a single room with an ensuite facility.

Contact and droplet precautions should be implemented.

Strict hand hygiene is the most important intervention.

Norovirus is unaffected by alcohol gel; hence, staff and visitors should use soap and water for handwashing.

WHO 5 moments of hand hygiene should be followed.

Staff caring for the patients should use appropriate personal protective equipment (PPE) – Disposable gloves, apron and fluid resistant surgical masks. Staff should risk assessing the need for eye/face protection.

The patient’s environment and instruments used should be cleaned with chlorine-based detergents. Norovirus can survive on any surface, including equipment and refrigerated food for up to 10 days.