Norovirus Infection: A Cause for Travelers' Concern?

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Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

A reported outbreak of norovirus infection on a cruise ship has 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.