What is norovirus infection?
Noroviruses refer to a group of viruses that cause inflammation of the stomach and intestines. This inflammation is called gastroenteritis, or the stomach flu. In the United States, noroviruses are the second leading cause of illness. Outbreaks have occurred in settings such as cruise ships, restaurants, nursing homes, and hospitals, locations where the virus can spread quickly to a large group of people.
The noroviruses are highly contagious. They are spread by fecal to oral contamination of water and food. Infection can occur through contaminated municipal water supplies, recreational lakes, swimming pools, wells, and water stored on cruise ships; by ingesting raw (or improperly steamed) shellfish, especially clams and oysters, and other foods and drinks that are contaminated by infected food handlers; and by touching contaminated surfaces such as door knobs and then touching one’s mouth. The viruses can also spread by direct contact with an ill person. This is common in day-care centers and nursing homes.
The following factors increase the chance of developing norovirus infection: exposure to a contaminated water supply, consuming contaminated foods or liquids, touching contaminated surfaces, and taking care of someone who is infected with the virus. A person is contagious from the start of symptoms to a minimum of three days after recovery. A person can sometimes be contagious up to three weeks.
Even if a person had been infected with a norovirus in the past, he or she can become ill again if this new virus is of a different strain or if more than twenty-four months have passed since the last exposure. Norovirus infection is more common in adults and older children than it is in the very young.
Symptoms of norovirus infection include nausea and vomiting (an infected person may vomit often, sometimes violently and without warning, during one day), diarrhea, abdominal pain, headache, low-grade fever, chills, muscle aches, tiredness, and dehydration. Dehydration may require medical attention, especially in children, the elderly, and those with compromised immune systems. One can prevent dehydration by drinking increased amounts of fluids, including water and juice.
After exposure to the virus, symptoms often appear within twenty-four to forty-eight hours. A person may feel ill as early as twelve hours. Symptoms often last about twenty-four to sixty hours.
Diagnosis can be made based on a stool specimen. Often, a doctor can determine this illness without ordering laboratory tests.
There are no treatments for norovirus infection. Because gastroenteritis is caused by a virus, antibiotics cannot cure it. There are no antiviral medications or vaccines. The illness, however, is often brief, and the only complication would be dehydration caused by vomiting and diarrhea. In certain groups of people, dehydration may require a hospital stay to replenish fluids.
Noroviruses can survive extreme heat and cold. The viruses also can live in water with chlorine levels of up to ten parts per million. (This is much higher than the levels of public water supplies.) There are ways, though, to limit exposure to the viruses.
To help reduce the chance of getting norovirus infection, one should wash hands thoroughly after using the toilet (or after changing diapers). This is important before handling food or eating. Caregivers should ensure that infected persons thoroughly wash their hands.
Food preparers should wash fruits and vegetables and steam oysters and clams. One should not prepare food if having symptoms and should wait three days after recovery before handling food again. Also, one should throw away contaminated food.
If ill or caring for someone who is ill, the caregiver should immediately clean and disinfect contaminated surfaces using bleach cleaner and should remove and wash soiled linens (using hot water and soap).
Sick persons should not go to work. Staying home will prevent passing the virus to others. If the norovirus-infected person works in a health care facility, sick persons in that facility should be isolated to keep the virus from spreading.
Centers for Disease Control and Prevention. “Outbreaks of Gastroenteritis Associated with Noroviruses on Cruise Ships--United States, 2002.” Morbidity and Mortality Weekly Report 51 (2002): 1112-1115.
Dolan, Raphael. “Noroviruses--Challenges to Control.” New England Journal of Medicine 357 (2007): 1072-1073.
Fankhauser, R. L., S. S. Monroe, J. S. Noel, et al. “Epidemiologic and Molecular Trends of Norwalk-Like Viruses’ Associated with Outbreaks of Gastroenteritis in the United States.” Journal of Infectious Disease, no. 186 (2002): 1-7.
National Institute of Allergies and Infectious Diseases. “Foodborne Diseases: Norovirus Infection.” Available at http://www.niaid.nih.gov/topics/norovirus.
“Norwalk Virus Family.” In The Bad Bug Book: Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition. Available at http://www.fda.gov/food/foodsafety/foodborneillness.