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Symptoms and Signs of Norovirus Infection

Doctor's Notes on Norovirus Infection

Norovirus is a common virus that infects humans. It is the most common cause of gastroenteritis (often referred to erroneously as “stomach flu”) in the US. People get the virus by ingesting food or drink that has been contaminated with small amounts of feces or fluids from infected people, such as occurs with poor handwashing. Foods and water may become contaminated during processing, preparation, or handling.

Characteristic signs and symptoms of norovirus infection are vomiting, nausea, and a watery diarrhea. The symptoms usually last 2-3 days and the go away on their own. Fluid lost through diarrhea and vomiting can lead to associated symptoms of dehydration, and young children and the elderly are most at risk for these complications. Other possible associated symptoms are fever, abdominal cramping, muscle aches, tiredness, and headache.

Medical Author:
Medically Reviewed on 3/11/2019

Norovirus Infection Symptoms

The symptoms and signs of norovirus infection usually occur within 12-48 hours of contact (incubation period) with the virus and often are first noticed within a cluster of people in a group (for example, military or school dorms, cruise ships, and nursing homes).

  • Groups of people (although occasionally individuals) rapidly develop nausea, vomiting, diarrhea, and abdominal discomfort or cramping.
  • Some people may develop a low-grade fever (less than 101 F), headache, weakness, muscle aches, and loss of taste. Diarrhea may be frequent (many watery stools in 12-24 hours).
  • For children, the elderly, pregnant women, or immunocompromised patients, diarrhea can lead to dehydration (body water loss).

The norovirus infection is usually self-limited and resolves in about one to three days, but people with severe dehydration can develop complications (for example, electrolyte imbalances, coma, or infrequently death).

Norovirus Infection Causes

Norovirus is transmitted from person to person. Ingestion of food or contact with other material contaminated with fluid or feces from a person infected with norovirus causes norovirus infection.

After an individual has contracted norovirus, it first attaches to cells in the gastrointestinal tract. The virus enters the cells, triggering the gastrointestinal tract to cause vomiting and preventing good fluid adsorption, which results in diarrhea. Because the virus is very difficult to cultivate in the laboratory, it has not been precisely determined exactly how the virus causes disease. The norovirus has been referred to by many names (for example, Norwalk virus, Norwalk-like virus or NLV, SRSV [small round structured viruses], and Snow Mountain virus). Many of these names often arise from the area or region where an outbreak occurs, like Toronto virus, Hawaii virus, or Bristol virus. Common names like "winter vomiting virus" or "stomach flu" are also used. "Stomach flu" is not related to any type of influenza; the term was likely coined because of the frequent watery diarrhea norovirus produces which is like the frequent clear or "watery" nasal discharge of the flu.

Viral Infection Types, Treatment, and Prevention Slideshow

Viral Infection Types, Treatment, and Prevention Slideshow

Viruses are small particles of genetic material (either DNA or RNA) that are surrounded by a protein coat. Some viruses also have a fatty "envelope" covering. They are incapable of reproducing on their own. Viruses depend on the organisms they infect (hosts) for their very survival. Viruses get a bad rap, but they also perform many important functions for humans, plants, animals, and the environment. For example, some viruses protect the host against other infections. Viruses also participate in the process of evolution by transferring genes among different species. In biomedical research, scientists use viruses to insert new genes into cells.

When most people hear the word "virus," they think of disease-causing (pathogenic) viruses such as the common cold, influenza, chickenpox, human immunodeficiency virus (HIV), and others. Viruses can affect many areas in the body, including the reproductive, respiratory, and gastrointestinal systems. They can also affect the liver, brain, and skin. Research reveals that that viruses are implicated in many cancers as well.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.