Norovirus

Background

• Noroviruses, also called Norwalk-like viruses, are a group of RNA viruses with over 30 genotypes (GI, GII, and GIV infect humans).
• They are the leading cause of viral gastroenteritis in adults in the UK.
• In young children (<5), rotavirus has traditionally been the most common, although norovirus is increasingly important since rotavirus vaccination.

Transmission

• Spread is typically person-to-person via the faeco-oral route.
• Transmission also occurs via aerosolised particles from vomit/diarrhoea, contaminated food and water, and contaminated surfaces.
• Very low infectious dose (10–100 viral particles) makes norovirus highly contagious.

Pathophysiology

• Noroviruses infect the small bowel epithelium (enterocytes), causing villous blunting, malabsorption, and secretory diarrhoea.
• Immunity is short-lived and strain-specific, so reinfections are common.
• Some individuals are genetically resistant to certain strains due to their histo-blood group antigen (“secretor status”).

Clinical features

• Incubation period: typically 24–48 hours (median ~24 hours).
• Symptoms: watery diarrhoea, nausea, malaise, fever, and often profuse vomiting.
• Illness usually lasts 12–60 hours, though longer in children, the elderly, or immunocompromised patients.

Diagnosis

• Usually a clinical diagnosis.
• PCR is the most sensitive and specific test. ELISA antigen detection is less sensitive.
• Laboratory confirmation is generally reserved for outbreak/public health purposes.
• For individual management, identifying the causative organism has little clinical impact.

Management

• Supportive care with oral or IV rehydration.
• Hygiene and infection control measures are key.
• Antiviral therapy is not indicated.

Epidemiology

• Outbreaks are common in hospitals, care homes, and schools.
• More frequent in winter but can occur year-round.
• Norovirus is not a notifiable disease in the UK, but institutional outbreaks are usually reported to Public health teams.