Noroviruses (Norwalk-like Viruses)

Fact Sheet about Noroviruses (Norwalk-like Viruses)

What are Noroviruses (Norwalk-like Viruses) ?

Norwalk virus, Norwalk-like viruses (NLV) or noroviruses are a group of viruses (germs) that cause diarrheal illnesses. These viruses are named after the original strain that caused an outbreak in Norwalk, Ohio. They are also sometimes referred to as small, round-structured viruses (SRSV) or caliciviruses.

What are the symptoms of NLV infection?

The symptoms of NLV infection include nausea, vomiting, diarrhea, and abdominal cramps. Other symptoms can include headache, fever, and chills, and muscle aches. These symptoms usually begin 1-2 days after exposure to the virus and will last about 1-2 days in most people, with no long-term effects.

How are NLV spread?

NLV must be swallowed to cause infection. NLV are then passed in the stool and vomit of infected people from the day they start to feel ill up to as long as 2-3 weeks after they feel better. NLV are usually spread by eating or drinking contaminated food or drinks or by close contact with an infected person. Foods can become contaminated by infected foodworkers. Some foods, like oysters and berries, can be contaminated with NLV before being delivered to a restaurant or store if they come in contact with contaminated water.

How common is NLV in Massachusetts?

NLV are believed to be one of the most common causes of foodborne illness in the United States. Since it is difficult to test for NLV in the laboratory; it is hard to say how many people get infected by NLV in Massachusetts.

Who gets NLV infection?

Anyone can get infected with NLV but older children and adults are more likely to get more severe symptoms. Also, since there are many strains of these viruses, people can get sick from them many times during their life.

How is NLV infection diagnosed?

NLV is difficult to detect in a laboratory, but it can be found by testing stool or vomit from an infected person. Only a few laboratories are able to perform this test so it is only done under special circumstances. Usually, health care providers will first try to rule out other germs that may have caused the illness, then base their diagnosis on symptoms and how long they last.

What is the treatment for NLV infection?

There is no specific treatment for NLV infection. NLV cannot be treated with antibiotics and people usually get better without medical attention in 1-2 days. There is a risk for dehydration due to vomiting and diarrhea so it is important to drink plenty of fluids. If symptoms persist or worsen, contact your health care provider.

What can you do to prevent NLV infection?

Follow the tips below; if you make them your habits, you can prevent infection by NLV – as well as other diseases:

  • Always wash your hands thoroughly with soap and warm water before eating or preparing food, after using the toilet, and after changing diapers.
  • Make sure all food preparation areas are clean before use.
  • Cook your food completely. Wash all fruits and vegetables.
  • When traveling to an area that might have contaminated water, drink bottled, preferably carbonated, beverages and do not use ice.
  • After episodes of vomiting or diarrhea, clean contaminated surfaces immediately with a bleach-based household cleaner.
  • If you are taking care of someone who has vomited or who has diarrhea, wash your hands with plenty of soap and warm water after cleaning the bathroom, helping the person use the toilet, or changing diapers, soiled clothes or soiled sheets.
  • If you or your child has persistent diarrhea (with or without a fever), or the diarrhea is very bad, call your health care provider for advice.

Are there any restrictions for people with NLV?

Yes. Because NLV can easily be spread to other people, health care providers are required by law to report cases of NLV to the local board of health. In order to protect the public, workers at food-related businesses who have NLV must stay out of work for 72 hours after their symptoms have stopped. In NLV outbreaks at food-related businesses, food handling employees will be required to provide stool specimens for testing. This law also applies to workers in schools, residential programs, day-care and health care facilities who feed, give mouth care or dispense medications to clients or patients.

For more information contact:

  • Your local board of health (listed in the telephone directory under “Government”)
  • Your health care provider
  • Massachusetts Department of Public Health: Division of Epidemiology and Immunization (617) 983-6800 or toll-free at (888) 658-2850 or on the MDPH website, or Division of Food & Drugs (617) 983-6700

Spanish and Portuguese translations of this fact sheet are available under additional resources.

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