Norovirus infection

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at October 10, 2016
StartDiseasesNorovirus infection

Viruses are a type of tiny biological agent that can infect the cells of the human body, so they are responsible for many highly infectious illnesses. Each year, millions of people suffer from painful viral infections due to the norovirus that causes a condition commonly known as the stomach flu but which is more accurately called gastroenteritis so as not to be confused with flu which is caused by the flu virus.


Definition & Facts

Norovirus infects roughly 267 million people per year, and in some cases, it can even be a fatal disease. When a person is infected by a strain of norovirus, they typically develop gastroenteritis. This is an inflammation of the stomach and intestines that causes many gastrointestinal symptoms.

Though norovirus normally only lasts a few days and is not too severe, it can be dangerous if a patient becomes dehydrated. Infants, seniors, and immunocompromised patients may end up needing to get emergency medical care if they develop a norovirus infection. 

Symptoms & Complaints

Symptoms of norovirus generally start to show up within one to two days of infection. This type of illness does not develop gradually. For many patients, the first sign of norovirus infection is a sudden bout of nausea and vomiting.

People tend to experience unpleasant abdominal cramps that often result in more vomiting as the infection progresses. When norovirus causes gastroenteritis, patients may experience excessively watery bowel movements or diarrhea. All of this gastrointestinal upset is often so severe that patients have difficulty eating or drinking anything.

Though most symptoms of a norovirus infection are gastrointestinal, it can cause a few other types of complaints. The non-gastrointestinal symptoms of a norovirus infection are somewhat similar to typical influenza. Norovirus may be accompanied by a mild fever, and it can also cause widespread muscular pain.

If patients vomit or have diarrhea for too long, they may become dehydrated. This causes a headache, dry skin, weakness, and dizziness. When norovirus infections include severe dehydration or bloody stool, it is necessary to seek medical care. Norovirus infection symptoms generally start to fade within three days, but patients can still be contagious even after they no longer show symptoms.


The symptoms of a norovirus infection are caused by infection with the norovirus. Since the virus can live for weeks on hard surfaces and years in liquids, it is very easy for humans to be infected by this virus. This type of virus is not harmed by extreme heat or cold, and even many typical disinfectants do not stop it from infecting others.

Humans are infected by norovirus when they ingest the virus pathogens. Infection often occurs after a person has consumed contaminated foods or beverages. Waterborne outbreaks of norovirus can happen after drinking water or ingesting small particles of contaminated water while swimming in it. A norovirus infection can also happen if a person touches a contaminated surface and then uses their hands to eat a food or touch their mouth.

Though norovirus infections are most caused by ingestion, it can also be caused by breathing air near a person with the virus because the virus can become airborne during vomiting. After being infected with norovirus, a patient will briefly maintain immunity to the virus, but they can get affected again after six to 24 months.

Diagnosis & Tests

Because the symptoms of norovirus are so apparent, doctors can typically diagnose this infection just by physically examining the patient. A norovirus diagnosis is particularly straightforward if the patient has been around someone else who recently suffered from a norovirus infection.

However, if a patient is exhibiting other symptoms due to unrelated health problems, the diagnosis can be trickier. When symptoms are caused by a combination of a norovirus infection and other health conditions, it is normally necessary to test the patient and see if there are traces of the norovirus within their body. There are tests available that examine stool samples for traces of the virus.

Most of these tests use polymerase chain reaction assays, so they are very quick and reliable. A norovirus stool sample analysis usually just takes a few hours, and it returns a positive diagnosis as long as there are just ten or more individual norovirus pathogen particles. ELISA antibody tests can also be used to detect norovirus, but they are not quite as sensitive to minor traces of the virus.

Treatment & Therapy

Since it is not a bacterial infection, norovirus cannot be treated with a simple course of antibiotics. Instead of curing the infection, gastroenteritis treatment relies on keeping the patient comfortable and relatively healthy while waiting on the virus to run its course. The main focus is providing fluids to avoid dehydration.

Patients typically benefit from water, tea, broths, and electrolyte-replacement sports drinks. The norovirus infection will only last a few days, and during this time it is mostly just important for the patient to get plenty of rest and liquids. If the diarrhea or nausea is very severe, people can end up in the hospital for norovirus treatment.

This type of treatment is normally just an intravenous hydrating solution and some anti-diarrhea and anti-nausea medications. If a patient is suffering from a low grade fever or body pain, some over-the-counter pain relievers can be useful. However, aspirin is not recommended for children with a viral infection because it can result in a rare but serious condition called Reye's syndrome.

Prevention & Prophylaxis

Norovirus prevention mostly relies on practicing proper hygiene. If possible, one should avoid anyone who is infected with a norovirus. Washing hands thoroughly with both soap and water before eating or handling food is also important.

All fruits and vegetables should be washed before eating, and meat or seafood should be cooked thoroughly. People caring for patients with norovirus should be careful to disinfect any contaminated substances with a solution made from chlorine bleach. If a patient is sick with a norovirus, they should try to stay home to prevent spreading the infection to others.