Norovirus Infection

Norovirus is the leading cause of acute gastroenteritis across all age groups in resource rich settings. It is a small, non enveloped ribonucleic acid virus of the Caliciviridae family.

Infectivity is extremely high because the infectious dose is very low and the virus is environmentally stable. It causes large outbreaks in closed or semi closed settings, including care homes, hospitals, cruise ships and schools.

Illness is typically brief but intense. Prominent, often projectile vomiting is very frequent.

Pathophysiology and transmission

The virus infects small intestinal enterocytes and causes transient injury. This produces malabsorption and secretory diarrhoea.

Transmission occurs by:

• the faecal oral route and direct person to person contact
• contaminated food or water. Shellfish, particularly oysters, are a recognised source because filter feeding concentrates virus from contaminated water.
• aerosolisation of vomitus, which contributes significantly to the rapid and extensive transmission seen in outbreaks

Outbreak settings need specific environmental and infection control measures beyond standard contact precautions alone.

Onset is acute, with vomiting that is often sudden, forceful and projectile. Watery diarrhoea and abdominal cramping accompany it. Incubation is short, 12 to 48 hours. Low grade fever, headache and myalgia frequently accompany the gastrointestinal symptoms.

The illness is typically brief, generally resolving within 24 to 72 hours in otherwise healthy individuals.

It can be more prolonged and cause significant dehydration in young children, elderly patients and those with significant comorbidity or immunocompromise. In significant immune impairment, chronic norovirus shedding and symptoms have been described.

The attack rate within affected settings is very high. This reflects the extremely low infectious dose, environmental persistence of the virus, and aerosolised transmission during vomiting. A single index case in a closed setting frequently leads rapidly to multiple further cases if control measures are not promptly instituted. This is relevant to outbreak recognition and control.

Diagnosis is generally clinical, based on the characteristic acute onset of vomiting and diarrhoea, particularly in the context of a recognised local outbreak or exposure to an affected setting, without the routine need for specific laboratory confirmation in individual, mild, self limiting community presentations.

Stool polymerase chain reaction testing provides sensitive and specific confirmation where pursued, particularly relevant for outbreak investigation and confirmation within institutional settings (care homes, hospitals), supporting appropriate infection control decision making and, where relevant, public health notification and broader outbreak management.

Management is entirely supportive. Oral rehydration therapy is the mainstay for the great majority of presentations.

Give small, frequent volumes. Prominent vomiting can make adequate oral fluid intake challenging without a careful, gradual approach.

Antiemetics, particularly ondansetron at standard age appropriate doses, support oral rehydration where vomiting is a significant barrier. Reserve intravenous rehydration for significant dehydration or failure of oral rehydration, following standard principles.

No specific antiviral treatment is available. Antibiotics have no role given the viral aetiology. The illness resolves spontaneously within a relatively short timeframe in the great majority of otherwise healthy individuals.

Rigorous infection control matters given the outbreak potential of this virus.

• Strict hand hygiene with soap and water. Alcohol based hand sanitiser is less effective against this non enveloped, environmentally resistant virus, similar to rotavirus.
• Prompt and thorough environmental cleaning with a chlorine based disinfectant effective against norovirus.
• Isolation or cohorting of symptomatic individuals within institutional settings.
• Exclusion of affected staff and, where relevant, visitors until at least 48 hours after complete resolution of symptoms. Viral shedding and infectivity continue during this period even after clinical recovery.

Recognise and report suspected outbreaks in institutional settings promptly to local infection control and public health teams. Transmission can be rapid and extensive. Timely control measures include, where necessary, temporary closure of affected wards or facilities to new admissions.