Norovirus Infection: A Cause for Travelers' Concern?

Reported outbreaks of norovirus infection on cruise ships 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.

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 contact with 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.

Norovirus is killed at temperatures above 60 C (140 F), so steaming or boiling (usual minimal time is one minute) can kill the virus. However, 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 not possible for an individual to completely prevent the infection. No vaccine is available, although a vaccine is in clinical trials with excellent preliminary results in children. 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. In summary, you can decrease your chances of contracting norovirus infection if you:

• Wash fruits and vegetables thoroughly before eating them
• Ensure that oysters and other shellfish are cooked thoroughly before consumption
• Disinfect kitchen surfaces with a bleached-based cleanser
• Wash laundry carefully if a person has experienced symptoms of norovirus infection. If possible, use disposable gloves to handle soiled laundry
• Avoid close contact with anyone with a gastrointestinal illness that includes nausea, vomiting, and diarrhea.
• Always remember proper hand washing with soap and warm water. Alcohol-based sanitizers may help in between washings, but these should not be used as a substitute for washing with soap and water.
• Never prepare food if you have symptoms of norovirus infection, and wait until you have been symptom-free for at least 3 days before resuming food preparation.