Norovirus Infection

Norovirus- Terminology Also known as (amongst other things) Winter vomiting virus Small Round Structured Virus Norwalk virus Belongs to the Calicivirus family (Sapovirus, another virus belonging to the Calicivirus family, can also cause gastroenteritis) Single stranded non-enveloped RNA virus

Bacteria Viruses Infective Parasites Diarrhoea Non-infective

Main Causes of Viral Gastroenteritis ROTAVIRUS Most common cause of severe diarrhoea in childhood, but not uncommon in adult populations. Endemic ENTERIC ADENOVIRUS Rotavirus-like childhood diarrhoea, endemic NOROVIRUS Causes most outbreaks of gastroenteritis, epidemic in all age groups ASTROVIRUS Endemic diarrhoea in young children, some outbreaks.

Norovirus Epidemiology Affects all age groups Patients with Blood group O most severely affected. 6 main genogroups (I-VI). I, II and IV can affect humans. Genogroups I&II most of human outbreaks. Genotype GII.4 main cause of outbreaks since 2002.

Norovirus Infected patients can shed billions of virus particles Infectious dose of 10-100 virus particles 24-48 hour incubation period 6-60 hour duration of illness A “mild” and short-lived illness Viral shedding of 2 weeks or more (However risk of transmission is likely to drop dramatically once symptoms settle)

Transmission of Norovirus Faecal oral Large droplet spread via aerosolised vomit Contaminated water Fomites Environmentally hardy Withstands heating to 60oc, freezing and chlorine concentrations up to 10 parts per million Best disinfectant for cleaning is household bleach (sodium hypochlorite) at 1 in 1000 dilution.

“A suspected outbreak” 2 or more patients with gastro-enteritis symptoms that are linked epidemiologically and with no other obvious cause for their symptoms. Factors making you think of Norovirus Vomiting Staff affected Short duration of symptoms New Cases Inform the ICN and Public Health promptly

Outbreak Management Case Definition Diarrhoea – 3 or more loose stools over 24/24 period Vomiting – 2 or more episodes over 24/24 period D’s & V’s – 1 or more episodes over 24/24 period (Exclude longstanding diarrhoea) (Exclude other causes)  

Clinical Features Diarrhoea 85% Nausea 81% Abdominal cramps 72% Vomiting 54% Low grade fever 51% Also joint pain, headache, rigors common 30% “asymptomatic infection” Vomiting more common in young Diarrhoea more common in elderly

Laboratory Testing Culture. Electron Microscopy Enzyme Immunoassay PCR Not feasible Electron Microscopy Catch-all Not practical for routine lab, slow, labour intensive Enzyme Immunoassay Poor sensitivity 50-60% PCR Current test, reasonably sensitive(80-90%), expensive Exclude bacteria, rotavirus, parasites and C.diff as cause of the outbreak. Typing can be considered if necessary to link individual cases.

Laboratory Testing- Norovirus One stool per patient. Vomitus can be tested but less sensitive. Stop testing when Norovirus has been confirmed in a particular ward/area.

Nursing during a Norovirus Outbreak Communication Hand Hygiene between patients is essential. Use of PPE (Personal Protective Equipment) Investigations should be “urgent only” particularly for symptomatic cases. Patient transfers to other wards should be restricted. Minimise the number of nurses looking after patients on an affected ward. If you contract Norovirus, then you should be asymptomatic for two days before returning to work. Restrictions on visiting.

Useful Resources on Norovirus http://www.cdc.gov/norovirus/hcp/index.html