Norovirus Details

What is Norovirus?

Noroviruses are a group of related micro-organisms in the family Caliciviridae that cause acute gastroenteritis in humans. Noroviruses can cause symptoms typically known as “stomach flu,” but the viruses are unrelated to the micro-organisms that cause seasonal influenza or other influenza, including the 2009 H1N1 flu (so-called swine flu). Symptoms from Noroviruses also are sometimes called food poisoning, although there are other causes of food poisoning that can be unrelated to Noroviruses, and people do not necessarily have to eat contaminated food to contract Norovirus-related illnesses.


Although Norovirus-related illnesses are usually not serious, they cause a significant amount of nausea, vomiting, diarrhea, and some stomach cramping. Those symptoms can make it difficult for some people to maintain sufficient fluids, and those individuals can become dehydrated. The viruses are very contagious and can spread rapidly, particularly in community settings such as nursing homes and day care facilities. The virus is most commonly spread on people’s hands and on contaminated surfaces. Frequent, thorough handwashing and proper surface disinfection are critical to preventing norovirus contamination and to stemming its spread within a facility where it does occur.


How do people become infected with Noroviruses?

Noroviruses are highly contagious, and are passed in the stool and vomit of infected people. Therefore, frequent, thorough handwashing and good surface disinfection protocols are critical to stem the spread of the illness.


People become infected when they:

  • touch surfaces or objects contaminated with the viruses, then touch their mouths;
  • have direct contact with a person who has contracted a Norovirus illness, such as caring for someone with the illness, or sharing food or utensils with a person who is ill;
  • eat food or drinking liquids contaminated by Norovirus.


Norovirus illness can spread very quickly in contained communities, such as day care facilities, nursing homes, overnight camps, hospitals, cruise ships, prisons and dormitories. 


When do symptoms appear?

Symptoms of Norovirus illness usually begin about 24 to 48 hours after ingestion of the virus, but they can appear as early as 12 hours after exposure. The illness usually comes on suddenly and the infected person typically feels very sick.


Symptoms typically include nausea, vomiting, diarrhea and stomach cramping. Some people also experience a low-grade fever, chills, headache, muscle aches and/or tiredness.


Symptoms typically last only one to two days. However, the person may remain contagious up to two weeks after they have recovered from the illness. Frequent, thorough handwashing is critical during this time.


Who gets sick from Norovirus infections?

Anyone can become infected with these viruses. There are several strains of Norovirus, which makes it difficult for a person’s body to develop a lasting immunity to the virus. Therefore, Norovirus illness can recur throughout a person’s lifetime. Some people are more likely to become infected and develop more severe illness than others.


How can the spread of Norovirus be contained?

Frequent, thorough handwashing is critical to the reduction in the spread of many illnesses, including Norovirus-related illnesses. Following good surface disinfection protocols also is critical.

Thorough handwashing is particularly important at these times:

  • after using the bathroom, changing a diaper, or assisting someone who is using the bathroom;
  • after caring for someone who is ill;
  • before preparing food or handling raw food;
  • before eating or feeding a child or other person.


If a person is ill, follow these steps to stem the spread of infection to others:

  • Immediately remove any clothing, towels or bed linen that becomes soiled from vomiting or diarrhea. Immediately wash the items in hot water and laundry detergent.
  • Flush or discard any vomit or stool in the toilet. Clean the surrounding area using an appropriate disinfectant or a household cleaner that contains chlorine bleach.
  • Utensils and dishes used by the sick person should not be used by any other person until the items are washed thoroughly in hot water and dish soap. The person who is ill should not prepare food for anyone else while they have symptoms and for three days after they recover. Any food that may have been contaminated by the sick person should be discarded.
  • Thoroughly clean and disinfect contaminated surfaces immediately after a person is ill. Use an appropriate disinfectant or a household cleaner that contains chlorine bleach.


What treatment is available for people with Norovirus infection?

There are no vaccines or antiviral medications that are effective against Norovirus. Norovirus infection cannot be treated with antibiotics; antibiotics fight bacteria, not viruses.


Dehydration is the most serious health effect that can result from Norovirus infection. Anyone who is ill with Norovirus infection should drink plenty of fluids to prevent dehydration. Young children, the elderly and those with other illnesses or conditions are most likely to be affected by dehydration. 


Are there other names for Norovirus-related illnesses?

The term Norovirus is a relatively new term for a group of viruses that have been known by other names. These other names include:

  •  Norwalk-like viruses (NLVs)
  •  Caliciviruses (because they belong to the virus family Caliciviridae)
  •  small round structured viruses.


Illnesses caused by Noroviruses are sometimes called:

  • stomach flu; (This is not related to seasonal influenza or 2009 H1N1 flu (so-called swine flu) which are respiratory illnesses.)
  • viral gastroenteritis; (The term “gastroenteritis” simply means an inflammation of the stomach and intestines.)
  • acute gastroenteritis;
  • non-bacterial gastroenteritis;
  • food poisoning; (There are also other causes of food poisoning.)
  • Calcivirus infection.
The information provided herein is, by its nature, only general guidelines and not specific to any person’s individual situation or circumstances and is not in any way intended to replace or supplant advice or treatment that would be provided by your doctor. If you feel that you have been exposed to, or are otherwise vulnerable to, any disease or illness, please consult with your doctor as soon as practical.