December 16, 2016

Norovirus - Symptoms, Treatment and Key Facts

Norovirus, also called winter vomiting bug in the UK, is the most common cause of viral gastroenteritis in humans. It is a very contagious virus that can be transmitted from person-to-person, and also from food, water or surfaces contaminated by feces or aerosolization of vomited virus.

Causative agent

Noroviruses (NoV) are a genetically diverse group of single-stranded positive-sense RNA, non-enveloped viruses belonging to the Caliciviridae family. According to the International Committee on Taxonomy of Viruses, the genus Norovirus has one species, which is called Norwalk virus.


Norovirus is called the "winter vomiting bug" because it's more common in winter (roughly from December to February, although November can often suffer very wintry conditions too), although you can catch it at any time of the year.

It causes about 18% of all cases of acute gastroenteritis worldwide. Thus, it is the most common pathogen implicated in outbreaks of gastroenteritis globally. It is relatively common in developed countries and in low-mortality developing countries (20% and 19% respectively) compared to high-mortality developing countries (14%). Proportionately it causes more illness in people in the community or in hospital outpatients (24% and 20% respectively) as compared with hospital inpatients (17%) in whom other causes are more common.

Norovirus affects people of all ages. Age and emergence of new norovirus strains do not appear to affect the proportion of gastroenteritis attributable to norovirus.

Norovirus is a common cause of epidemics of gastroenteritis on cruise ships. The US Centers for Disease Control and Prevention through its Vessel Sanitation Program record and investigate outbreaks of gastrointestinal illness—mostly caused by norovirus—on cruise ships with both a U.S. and foreign itinerary; there were 12 in 2015, and 10 from 1 January to 9 May 2016. An outbreak may affect over 25% of passengers, and a smaller proportion of crew members.


Noroviruses are transmitted directly from person to person (62–84% of all reported outbreaks) and indirectly via contaminated water and food (i.e. fecal-oral and contamination). They are extremely contagious, and fewer than twenty virus particles can cause an infection (some research suggests as few as five).

Transmission can be aerosolized when those stricken with the illness vomit, and also can be aerosolized by a toilet flush when vomit or diarrhoea is present; infection can follow eating food or breathing air near an episode of vomiting, even if cleaned up. The viruses continue to be shed after symptoms have subsided and shedding can still be detected many weeks after infection.

Signs and Symptoms

Norovirus causes inflammation of the stomach or intestines or both leading to acute gastroenteritis. Symptoms often start with sudden onset of vomiting and/or diarrhoea.

The most common symptoms are diarrhoea, throwing up, nausea, and stomach pain. Other symptoms may include fever, headache, and body aches.

A person usually develops symptoms 12 to 48 hours after being exposed to the virus. Most people with Norovirus illness get better within 1 to 3 days.

If you have Norovirus illness, you can feel extremely ill and throw up or have diarrhoea many times a day. This can lead to dehydration, especially in young children, older adults, and people with other illnesses.


There is no specific medicine to treat people with the illness. Norovirus infection cannot be treated with antibiotics because it is not a bacterial infection. Treatments aim to avoid complications such as dehydration from fluid loss caused by vomiting and diarrhoea, and to mitigate symptoms using antiemetics and antidiarrheals.

Oral fluids should be taken as can be tolerated to replace fluid lost from throwing up and diarrhoea. This will help prevent dehydration. Severe dehydration may require hospitalization for treatment with intravenous fluids.

Preventing Norovirus infection

It's not always possible to avoid getting Norovirus, but following the advice below can help stop the virus from spreading.
  • Stay off work or school until at least 48 hours after the symptoms have passed. You should also avoid visiting anyone in hospital during this time.
  • Wash your hands frequently and thoroughly with soap and water, particularly after using the toilet and before preparing food. Don't rely on alcohol hand gels, as they do not kill the virus.
  • Disinfect any surfaces or objects that could be contaminated. It's best to use a bleach-based household cleaner.
  • Wash any items of clothing or bedding that could have become contaminated separately on a hot wash to ensure the virus is killed.
  • Don't share towels and flannels.
  • Flush away any infected poo or vomit in the toilet and clean the surrounding area.
  • Avoid eating raw, unwashed produce and only eat oysters from a reliable source, as oysters can carry norovirus.
Also read: How to Wash Your Hands the Right Way to Stay Healthy

1). World Health Organization: Communicable diseases - International travel and health. Accessed 13 December 2016. Available here:
2). World Health Organization: WHO’s first ever global estimates of foodborne diseases find children under 5 account for almost one third of deaths - Media Center. Accessed 13 December 2016. Available here:
3). NHS Choices: Norovirus. Accessed 13 December 2016. Available here:
4). Centers for Disease Control: Norovirus. Accessed 13 December 2016. Available here:
5). Wikipedia, The Free Encyclopedia: Norovirus. Accessed 13 December 2016. Available here:


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