Norovirus

Background

Norovirus, also known as Norwalk virus and commonly referred to as the winter vomiting bug, is the most common infectious cause of vomiting and diarrhoea in adults in the UK. Norovirus is a single-stranded positive-sense RNA non-enveloped virus. Norovirus is highly contagious with only a small number of viral particles (as few as 18) needed to cause infection.

Epidemiology

In the UK, seasonal peaks tend to occur in the winter months, particularly between November and April. It is a major contributor to outbreaks in healthcare settings, care homes, schools, and cruise ships, often leading to significant public health and economic burdens. The virus is responsible for over 60% of all cases of infectious gastroenteritis in the UK.

Incubation Period

The typical incubation period for norovirus is 12 to 48 hours following exposure. Symptoms often begin suddenly and resolve within 1–3 days in otherwise healthy individuals.

Modes of Transmission

Transmission primarily occurs via the faecal-oral route including:

• Direct contact with infected individuals
• Consumption of contaminated food or water
• Contact with contaminated surfaces or fomites
• Aerosolised vomit particles that can settle on surfaces or be inhaled

In hospitals, nosocomial transmission can lead to widespread outbreaks, requiring ward closures and significant infection control efforts. The virus is resistant to many disinfectants and can survive on surfaces for days, making stringent hygiene and decontamination measures essential.

Pathological Basis

Norovirus primarily targets the epithelial cells of the small intestine, where it causes disruption of the brush border, leading to malabsorption, increased intestinal permeability and transient inflammation.

This typically results in non-bloody, watery diarrhoea, often accompanied by vomiting, abdominal pain, fever, and malaise. The disease is self-limiting in healthy individuals but can cause severe dehydration, particularly in the elderly, very young, or immunocompromised.

Clinical Features

• Sudden onset vomiting and watery diarrhoea
• Abdominal cramps
• Low-grade fever
• Headache and fatigue
• Dehydration can occur especially in vulnerable populations

Diagnosis
Diagnosis is often clinical during outbreaks, based on symptom clusters and rapid onset. Laboratory confirmation is important for public health monitoring. RT-PCR (NAAT) of stool samples is the gold standard.

Management

Management is mainly supportive with a focus on maintaining hydration via fluid replacement. Prevention of further spread is via good hygiene measures and limiting exposure to others.

Public Health Implications

Due to its high transmissibility and environmental persistence, norovirus outbreaks necessitate:

• Exclusion from work or school for at least 48 hours after symptoms resolve
• Enhanced infection control in hospital wards and communal environments
• Notification and surveillance to manage and prevent large-scale outbreaks