Norovirus

Norovirus, also known as the winter vomiting bug, is one of the most common causes of gastroenteritis in the UK according to NHS England. It is a genus that encompasses a range of non encapsulated RNA virus species. The CDC (Centre for Disease Prevention and Control) estimates that 1 in 5 cases of infectious gastroenteritis are caused by norovirus, with 685 million cases per year worldwide.

• Develop within 15 - 50 hours of infection (quoted from the European Centre of Disease Control and Prevention), with patients experiencing nausea, vomiting, and diarrhoea, which may be accompanied by headaches, low-grade fevers, and myalgia.
• The majority of patients experience both vomiting and diarrhoea
• 10 - 22% reported a headache and up to 47% of patients reported fevers (Clinical Microbiology Reviews, Norovirus, January 2015)

• Faecal-oral route, with the virus becoming aerosolized when the patient vomits or when a toilet containing infected bodily fluids (vomit or faeces) is flushed.
• Viral particles are transmitted directly to surrounding potential hosts and to surrounding surfaces, from which they can be transmitted by cross-contamination (for example a patient visitor touching the patient environment, then eating without first washing their hands).
• Infection may also be transmitted from an infected individual in the process of direct physical contact, or contact with food preparation.
• The virus enters the cell via host receptor-mediated endocytosis and replicates in the small intestine. Norovirus is highly contagious, the European Centre of Disease Control and Prevention estimates that only 10 - 100 viral particles are required to cause an active infection.
• Norovirus is not at present considered to be a notifiable disease in the UK.

• Isolation of infected strongly recommended where possible, particularly in areas where the risk of person to person transmission is high, for example, in hospitals schools, and care facilities
• Good hand hygiene using soap and water is essential
• Alcohol hand gel has been shown to be less effective in reducing transmission

• Clinical history and stool culture viral PCR (polymerase chain reaction).

• Features most suggestive of norovirus include sudden onset vomiting, relatively short duration of symptoms and contact with others with similar symptoms.
• Rotavirus, E. coli and Salmonella infections will all cause similar clinical pictures, however, there are some important differentiating features.
• Salmonella infection has an incubation period of 6 - 72 hours and is often the result of contact with contaminated animal products, for example, unpasteurized eggs or milk. Unlike norovirus, salmonella gastroenteritis can cause bloody diarrhoea and patients often have a high fever.
• Rotavirus gastroenteritis causes symptoms very similar to those of norovirus, but predominantly affects children under the age of 5 years.
• E. coli infection, like Norovirus, causes vomiting and diarrhoea but has a longer incubation period (between 3-4 days but can be up to 10 days following pathogen exposure) and unlike Norovirus, E Coli infection commonly causes severe abdominal cramping and frequently causes bloody diarrhoea.

• The infection is self-limiting in immunocompetent patients and symptoms generally resolve within 72 hours
• Dehydration and electrolyte imbalances may arise as a result of vomiting and diarrhoea, leading to significant morbidity and mortality and patients should be managed supportively with rehydration and electrolyte supplementation where necessary.