Noroviruses are part of a group of viruses that are the most common cause of gastroenteritis (upset stomach) in the UK. They're also known as the 'winter vomiting disease' because people usually get them during the winter months. However, they can occur at any time of the year.
There have been a series of "outbreaks" of such tummy upsets onboard various different ships in the last few years. It's nothing to worry about but if you understand what it is, it might help you understand what's happening if you ever are onboard a ship and people are being confined to their cabins...
How noroviruses are spread
It is estimated that the norovirus affects between 600,000 and one million people in the UK every year. Outbreaks of the illness are common, particularly within contained environments such as hospitals, nursing homes and schools - and so it's not uncommon on a cruise ship. This is because the norovirus spreads very easily from person to person and it can survive for several days in a contaminated area.
The norovirus can be spread through contact with an infected person, through contact with surfaces or objects that are contaminated with the virus, or by eating contaminated food or water.
There are many types of norovirus, and it is possible for infection to occur several times. This is because after getting the illness immunity to the virus only lasts for 14 weeks. Having recurring bouts of the norovirus may provide some protection from future infection.
Click here for a great resource on occurrences of noroviruses on ships
According to Medical Author: Melissa Conrad Stöppler, MD and Medical Editor: William C. Shiel Jr., MD, FACP, FACR, reported outbreaks of norovirus infection on cruise ships have left many would-be travelers worried about contracting the illness and wondering if they can prevent it. Many people may not be familiar with the term norovirus, but it's actually a relatively new term for an old disease. The many strains of noroviruses cause a self-limited gastrointestinal illness that many refer to as the "stomach flu." Outbreaks of norovirus infection have also been documented as coming from restaurants, schools, and nursing homes. Norovirus is now the official name for the group of viruses that, for a time, were referred to as "Norwalk-like" viruses, after the original strain "Norwalk virus," which caused an outbreak of gastroenteritis in a school in Norwalk, Ohio, in 1968. Other names for this group of viruses have included caliciviruses (the virus family name) and small round structured viruses (SRSVs).
After infection with one of the noroviruses, symptoms typically appear within one to two days. The sudden onset of nausea and vomiting, watery diarrhea, and abdominal cramping are the most common symptoms of norovirus infection. A low-grade fever may be present. The illness typically resolves on its own within 24 to 60 hours without serious long-term effects. However, dehydration is a potential complication, especially among children and the elderly, possibly requiring medical treatment.
Norovirus infection is very contagious. This is why rapid outbreaks can easily occur when many people are confined to a relatively small environment, such as on a cruse ship. It is estimated that noroviruses are responsible for at least 50% of cases of food-related gastroenteritis. The infection is spread by the fecal-oral route, meaning that people can get the infection by consuming contaminated food or water or directly from infected individuals. Since there are multiple strains of norovirus and it is unclear how long immunity to a particular strain can last, people can develop multiple norovirus infections throughout their lifetime.
Diagnostic tests are available at state reference laboratories to identify norovirus and are used to determine the cause of major outbreaks of illness (such as the cruise-ship outbreaks), but tests for norovirus are not routinely performed when an individual develops the stomach flu since there is no treatment specific for norovirus infection.
Noroviruses are able to survive freezing, temperatures as high as 60°C, and have even been known to cause illness after being steamed in shellfish. The viruses can also survive in chlorine levels greater than those normally present in public water systems. Because the viruses are so hardy and highly contagious, it is likely not possible for an individual to completely prevent the infection. However, safe hygienic practices in the handling of food and water, appropriate isolation of infected people (not allowing those with gastrointestinal illness to prepare or handle food and drink), and disinfection of contaminated surfaces can help avoid spreading the infection.
Reference: U.S. centers for Disease Control and Prevention (CDC): Norovirus fact sheet, accessed 3/5/2008.
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