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17 May 2017
Norovirus Infection  

Causative agent

Norovirus infection typically causes acute gastroenteritis. It is also a common cause of food poisoning and is usually related to consumption of undercooked shellfish. People can also get norovirus from an infected person, contaminated food or water, or by touching contaminated surfaces. Norovirus can also cause outbreaks of acute gastroenteritis in settings where people are staying close together such as schools, elderly homes, hotels and cruise ships. The disease affects people of all age groups and tends to be more common during winter. The virus is previously known as ‘Norwalk-like viruses’.

Clinical features

Symptoms include nausea, vomiting, diarrhoea, abdominal pain, low-grade fever and malaise. The symptoms are usually self-limiting, most people will get better within 1 – 3 days.

Modes of transmission

The infection can be transmitted via the following ways:

  1. by food or water contaminated with the virus;
     
  2. by contact with vomitus or faeces from infected persons;
     
  3. by contact with contaminated objects; or
     
  4. by aerosol spread with contaminated droplets of splashed vomitus.

Incubation period

The incubation period is usually 12 – 48 hours.

Management

Given adequate fluids to prevent dehydration and supportive treatment, the patient usually recovers within 1 – 3 days. Antibiotics are of no value in treatment.

Prevention

No vaccine is available for norovirus infection. As a general measure to prevent gastroenteritis, members of public are advised to:

Maintain good personal hygiene

  • Wash hands thoroughly with liquid soap and water before handling food or eating, and after using the toilet or handling vomitus or faecal matter.
     
  • Refrain from work or school, and seek medical advice if suffering from fever, vomiting or diarrhoea.
     
  • Exclude infected persons and asymptomatic carriers from handling food and from providing care to children, elderly and immunocompromised people.

Maintain good food hygiene

  • Adopt the 5 Keys to Food Safety in handling food, i.e. Choose (Choose safe raw materials); Clean (Keep hands and utensils clean); Separate (Separate raw and cooked food); Cook (Cook thoroughly); and Safe Temperature (Keep food at safe temperature) to prevent foodborne diseases.
     
  • Drink only boiled water from the mains or bottled drinks from reliable sources.
     
  • Avoid drinks with ice of unknown origin.
     
  • Purchase fresh food from hygienic and reliable sources. Do not patronise illegal hawkers.
     
  • Wash and peel fruit by yourself and avoid eating raw vegetables.
     
  • Cook all food, particularly shellfish, thoroughly before consumption.

* Please visit the website of Centre for Food Safety for more information on food safety.

Maintain good environmental hygiene

  • Maintain good indoor ventilation.
     
  • Cleanse vomitus/ faeces and disinfect the contaminated areas properly and immediately (please refer to the guidance on disinfection below for details). Keep other people away from the contaminated areas during cleansing.
     
  • Wear gloves and a surgical mask while disposing of or handling vomitus and faeces, and wash hands thoroughly afterwards.
     
  • Maintain proper sanitary facilities and drainage system.
     
  • Cleanse and disinfect toilets used by infected person and the soiled areas.

Guidance in disinfection of area contaminated by vomitus/ faecal spillage from patients with norovirus infection

  • Keep other people away from the contaminated area.
     
  • Wear gloves and a surgical mask throughout the disinfection procedure.
     
  • Discard all food if vomiting and diarrhoea occurs in an area where open food is displayed.
     
  • Remove the bulky waste cautiously from all soiled linens and clothing before washing. Then, soak them in 1 in 49 diluted household bleach for 30 minutes and then wash thoroughly. If immediate washing cannot be arranged, place the soiled linens and clothing inside sealed bags and wash them as soon as possible.
     
  • Use disposable towels to wipe away all the vomitus/ faecal spillage from outside inward. Then apply 1 in 49 diluted household bleach to the contaminated surface and the adjacent areas liberally (as a rough guide, preferably disinfect areas within 2 metres from the edge of the vomitus/ faecal spillage), especially the frequently touched surfaces e.g. door knobs, hand rail, etc. Leave bleach on the soiled surface for 15 – 30 minutes to allow time for the bleach to inactivate viruses. Then rinse the surface with clean water. Leave the surface air dry. For metallic surface, disinfect with 70% alcohol. 
  • Never use floor mops for cleaning up the vomitus.
     
  • Soak all cleaning tools in 1 in 49 diluted household bleach for 30 minutes and then rinse thoroughly before reuse.
     
  • Wash hands thoroughly afterwards.
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