Norovirus Infection

Norovirus ("stomach flu") is a very contagious illness that causes symptoms such as vomiting, diarrhea, nausea, and abdominal cramps.

• Norovirus is a virus that causes nausea, vomiting, and diarrhea, known as acute gastroenteritis or "stomach flu."
• Norovirus is the most common cause of food-borne disease outbreaks in the U.S.
• Norovirus is highly contagious and often occurs in outbreaks where people are in close contact, such as dorms, cruise ships, or nursing homes.
• Symptoms of norovirus typically last for one to three days.
• Norovirus infection typically resolves on its own with an excellent prognosis. The elderly, people with suppressed immune systems, and those with chronic health conditions may develop complications.
• There is no vaccine currently available to prevent norovirus infection.
• Because there are multiple strains of the virus and the fact that the body does not produce a strong immune response to the infection, experts believe it is possible to contract norovirus infection more than once in a lifetime.
• No specific treatment is generally required for norovirus, but it is important to maintain good hydration.
• Hand washing and good hygienic practices are key to preventing the spread of norovirus infection. Proper cooking and handling of food supplies can prevent outbreaks.

• Norovirus is a common viral infection that causes a person to develop a rapid onset of nausea, vomiting, diarrhea, and occasionally stomach cramping (all symptoms of gastroenteritis). In addition, the person may feel tired, have muscle aches, a headache, and a low-grade fever (less than 101 F) with chills. The symptoms last about one to two days. Although no long-term problems persist or develop with this viral infection, dehydration (loss of body water) may be significant enough to require medical treatment.
• Norovirus was probably first noticed by Dr. J. Zahorsky in 1929 and termed "winter vomiting disease." In 1968 in Norwalk, Ohio, there was an outbreak of gastroenteritis thought to be caused by a virus. The virus was termed the Norwalk agent (also termed particle or virus). It was classified as a "small round virus" and later, after genetic studies, classified as a member of the family Caliciviridae, with a single strand of RNA for its genome. The name of the genus, Norovirus, was approved in 2002 by an international committee.
• Researchers suggest norovirus is responsible for about 50% of all outbreaks of gastroenteritis in the U.S. and about 90% of epidemic nonbacterial gastroenteritis outbreaks worldwide. It is the most common cause of outbreaks of food-borne illness in the U.S. Most outbreaks or epidemics occur in places where people come together in close contact (for example, dorms, hospitals, prisons, cruise ships, schools, and nursing homes). Norovirus infections are transmitted from person to person, by contaminated food and water, and by contact with norovirus-contaminated surfaces.

• 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.

Norovirus is highly contagious from person to person. It is mainly spread by the fecal-oral route from person to person, either directly by contact with an infected individual or indirectly by contaminated foods or surfaces. The virus is also spread by droplets in the air (usually by droplets associated with vomiting), and if the droplets land on food or other objects, the virus can be transmitted to the mouth when touched by the hands.

Contaminated food is a common means of spread. Contamination of food occurs when infected people handle or prepare food under improper hygienic conditions. Foods that become contaminated with norovirus and are commonly involved in outbreaks of norovirus illness include

• leafy greens,
• fresh fruits, and
• shellfish.

Researchers have shown that human noroviruses can be carried by other animals such as dogs, which can transmit viruses to humans. Consequently, some investigators consider norovirus infections to be a zoonotic disease (a disease transferred between animals and humans).

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).

• Anyone can contract a norovirus infection. The virus infects both children and adults.
• Since the virus is spread from other infected people, risk factors include large group settings where people are in close contacts, such as dorms, hospitals, prisons, cruise ships, schools, and nursing homes.

• Symptoms and signs of a norovirus infection usually last from one to three days.

People with norovirus infection are contagious as soon as they begin to feel ill. They may remain contagious for about three days after they've recovered, but some people can remain contagious for up to two weeks after recovering.

In most cases of norovirus infection, medical care is not necessary as the infection resolves on its own without specific treatment. However, if replacement fluids cannot be or are not taken orally to keep a person hydrated, medical care should be sought.

• This inability to rehydrate is more often seen in infants, young children, the elderly, and in immunosuppressed people.
• Increased lethargy, decreased fluid intake, and decreased urination (signs of dehydration) often are indications medical care should be obtained.
• Patients with extensive vomiting may be at a high risk for dehydration or esophageal damage; these patients should also seek medical care.

• Most state laboratories in the U.S. have a reverse transcriptase polymerase chain reaction test (RT-PCR) that is very sensitive and specific for detecting the genetic material of norovirus. Stool, vomit, and environmental swabs can be used as samples for this test.
• Other diagnostic tests have been used for norovirus infection (for example, electron microscopy, serum antibody increases, and ELISA), but these tests are done infrequently and often are less sensitive and specific than RT-PCR.
• Testing outbreaks for norovirus is important because such testing can rule out diseases with similar symptoms (for example, diseases caused by rotavirus, Vibrio, Escherichia, and other organisms).

In the majority of norovirus infections, medical treatment is not required because most infections are self-limited and resolve with no lingering problems. Oral intake of fluids is recommended for all people with norovirus infection to avoid dehydration. People with severe nausea and vomiting are often given medicines to reduce or stop vomiting. Individuals who become dehydrated may require intravenous fluids with electrolytes to avoid complications of dehydration. A few severely dehydrated patients may require hospitalization.

• The best self-care with norovirus infection is to stay well hydrated with fluids. Although water helps to hydrate the body, it does not provide replenishment of the electrolytes the body loses rapidly with vomiting and diarrhea. Consequently, for adults, clear fluids (for example, sports drinks, Sprite, juices without any pulp, bouillon) are recommended.
• For children, commercially available solutions that do not require a prescription (for example, Pedialyte, Enfalyte, and Pediatric Electrolyte) are recommended. After each watery stool, the person should attempt to take in fluid roughly equal to the amount excreted (about 1-3 ounces for children under the age of 2, 3-8 ounces for older children, and 8 or more ounces in adults).
• Pregnant women with norovirus infections tend to become dehydrated faster than others, so they should rehydrate quickly. If a pregnant woman fails to take in adequate fluids and start to become dehydrated, seek medical care immediately.
• Most physicians do not recommend taking over-the-counter antidiarrheal medications such as diphenoxylate atropine (Lomotil) or loperamide hydrochloride (Imodium) because they may prolong the infection or cause complications.
• Since many underdeveloped countries have no commercially made electrolyte solutions available (both oral and IV), the World Health Organization (WHO) recommends the following for fluid rehydration, especially for children because they have a smaller fluid and electrolyte reserve than adults: Mix 2 tablespoons of sugar with ¼ teaspoon of table salt with ¼ teaspoon of baking soda in 1 liter of clean (treated or boiled) water. Other investigators suggest adding about ½ cup of clear (no pulp) fruit juice to this solution to provide added potassium.

• There is no specific drug available to treat norovirus infection.
• People with severe nausea and vomiting are often given medicine (for example, promethazine [Phenergan], prochlorperazine [Compazine], or ondansetron [Zofran]) intravenously to reduce or stop vomiting. If this is effective, patients may later receive oral or rectal preparations of these drugs and be monitored in the clinic by their physician.
• Individuals who become dehydrated may require intravenous fluids with electrolytes to avoid complications of dehydration. A few severely dehydrated patients may require hospitalization until their fluids and electrolytes are replenished.

• If the symptoms listed above for norovirus infection persist longer than three days or the person becomes dehydrated, medical help should be sought. Patients who are immunosuppressed, infants, and the elderly should follow up with their doctor to avoid getting dehydrated.
• People with norovirus infection should not return to work until about three days after all symptoms have resolved. Strict hygiene with good hand washing needs to be emphasized for these individuals, as some people shed virus in their feces for two weeks after symptoms resolve.
• A bland diet is recommended for children and adults as the symptoms of the norovirus infection diminish. Food items such as rice, bread, bananas, applesauce, pasta, and clear fluids are suggested.

• Norovirus infection typically resolves on its own without any adverse consequences in healthy people who receive adequate hydration and the prognosis is generally excellent.
• People with suppressed immune function, the elderly, or those with chronic medical conditions may have a higher risk of complications from the infection.

• The best method for prevention of norovirus infection is frequent hand washing and excellent hygiene, although hand sanitizers and washing are not absolutely effective. Avoid contact with any vomit or feces from ill individuals; discard the material in a toilet and clean any clothing and areas that may have come in contact with the material. Hot water and soap can help clean clothes. Because norovirus has been reported to survive on surfaces up to four weeks at room temperature, disinfection is recommended with commercial products or a solution of ½ cup of bleach to 1 gallon of water.
• Wash all linens and clothes immediately if they have come into contact with vomit or feces from an infected person.
• Carefully wash fruits and vegetables before preparing and eating them. Cook oysters and other shellfish thoroughly before eating them. Noroviruses are relatively resistant and can survive temperatures as high as 140 F and quick steaming processes that are often used for cooking shellfish. Many local and state health departments require that people with norovirus illness who work with food or prepare food not work until at least 48 hours after symptoms stop.
• Because of the potentially long (about two to four weeks) environmental survival of the virus at room temperature, often an area in which an outbreak occurs will need to be disinfected. Repopulating an area with uninfected people without disinfecting the area may produce another outbreak. Consequently, areas (for example, dorms, barracks, cafeterias, and cruise ships) should be disinfected after a norovirus outbreak to prevent further infections.
• There is currently no vaccine for norovirus. There are many different strains of the virus, which makes vaccine development difficult. Even the body's immune defense mechanisms have difficulty producing effective immune responses to norovirus. In addition, the infection is short-lived and usually self-limiting so some investigators suggest the body does not produce good immune responses to this infection. Although all of the reasons are not understood in detail, it is clear that most individuals can be reinfected with norovirus.