Norovirus was first identified in 1972 as the cause of a gastroenteritis outbreak in Norwalk, Ohio, and it became famous because of severe outbreaks on cruise ships in 2002.

Global Trends

Norovirus is the most common cause of acute gastroenteritis, annually causing an estimated 685 million cases. About 200 million cases are seen among children under 5 years old, leading to an estimated 50,000 child deaths every year, mostly in developing countries. However, norovirus illness is a problem in both low- and high-income countries.

Every year, norovirus is estimated to cost $60 billion worldwide due to healthcare costs and lost productivity. Norovirus illnesses and outbreaks are usually more common in cooler winter months. The majority of all outbreaks occur from November to April in countries above the equator, and from May to September in countries below the equator. However, in places closer to the equator, norovirus may be less seasonal.


Since 2002, GII.4 viruses (genogroup II genotype 4) have caused the majority of norovirus outbreaks worldwide. Although in recent years, non-GII.4 viruses, such as GII.17 and GII.2, have temporarily replaced GII.4 viruses in several Asian countries. Between 2002 and 2012, new GII.4 viruses emerged about every 2 to 4 years, but since 2012, the same virus (GII.4 Sydney) has been the dominant strain worldwide. Often, but not always, these new strains lead to a global increase in norovirus outbreaks.

Norovirus Spreads Easily

Norovirus spreads in the feces and vomit of people and animals with the infection. People with norovirus illness can shed billions of norovirus particles. And only a few virus particles can make other people sick.You can get norovirus from: having direct contact with an infected person, consuming contaminated food or water, touching contaminated surfaces and then putting your unwashed hands in your mouth, you can get norovirus illness many times in your life because there are many different types of noroviruses.Infection with one type of norovirus may not protect you against other types. It is possible to develop immunity to specific types. But, it is not known exactly how long immunity lasts. This may explain why so many people of all ages get infected during norovirus outbreaks. Also, whether you are susceptible to norovirus infection is also determined in part by your genes.


Although norovirus more commonly causes infection during the winter months, it can affect people at any time of the year. People sometimes incorrectly refer to a norovirus infection as “stomach flu.” The medical term is gastroenteritis, and it does not have a connection with the flu, which is a respiratory infection.Typically, the first symptom of norovirus is nausea. Other common symptoms include : vomiting, stomach pain, abdominal cramps, watery or loose diarrhea, feeling unwell and lethargic, fever and chills, which are usually mild, body aches and headaches.

During the brief period when symptoms are present, people can feel very ill and vomit many times a day, often violently and without warning. Signs and symptoms usually last 1–3 days and appear between 12 and 48 hours after the initial infection. In some cases, diarrhea may last longer than 3 days. It is important to note that once the symptoms have resolved, the virus can still spread through the stool and vomit for 2 weeks.

Risk Factors

Here’s All to Know about Norovirus

Risk factors for becoming infected with a norovirus include: eating in a place where food has been handled by someone with norovirus infection or the food has been in contact with contaminated water or surfaces, attending preschool or a child care center, living in close quarters, such as in nursing homes, staying in hotels, resorts, cruise ships or other destinations with many people in close quarters, having a weakened immune system and having contact with someone who has norovirus infection.

Outbreak Risk Factors

About 70% of foodborne norovirus infection outbreaks occur due to the direct contamination of food by a handler with norovirus immediately before its consumption. Outbreaks have often had links to cold food, including salads, sandwiches, and bakery products.Authorities have also implicated liquid food items, such as salad dressing and cake icing, as outbreak causes. Sometimes, oysters from contaminated waters have taken the blame for widespread gastroenteritis outbreaks. Sewage contamination of wells and recreational water has also caused waterborne outbreaks of norovirus infection in community settings.


In the vast majority of cases, a norovirus infection resolves itself within a few days and has no complications. Less commonly, the following complications may occur: malnutrition, constipation, dyspepsia and refluxSome people are unable to drink enough liquids to replace those that they lose through vomiting or diarrhea. They may become dehydrated and require special medical attention. Young children, older adults, and individuals of any age who need a caregiver are especially vulnerable.

Causes of The High Communicability of Norovirus

The infectious dose is very low (18–100 particles), and patients of all ages are susceptible. High levels of viral shedding can precede illness onset. Shedding gradually decreases over days to weeks but can last for months in patients who are immunocompromised. The virus is stable for a long time in the environment at temperatures from 0°C to 60°C.The virus is dispersed by projectile vomiting.

There are many modes of transmission (e.g., person-to-person contact, droplets, contaminated fomites, environment, food, water). Norovirus has a high degree of genetic and antigenic diversity because of mutations and recombination.

Infection results in short-term immunity with incomplete cross-protection among strains. Repeat infections can occur throughout life, creating a large human reservoir. After a norovirus infection, people have temporary immunity from further infection, although this usually only lasts for about 2–3 years.

Prevention of Norovirus Infection


Wash your hands thoroughly with soap and water for at least 20 seconds, especially after using the toilet or changing a diaper and before you prepare food and eat or drink. Alcohol-based hand sanitizers aren’t as effective against noroviruses as using soap and water.

Avoid contaminated food and water, including food that could have been prepared by someone who was sick. Wash fruits and vegetables before eating. Cook seafood thoroughly.

Disinfect surfaces that might have been contaminated. Wear gloves and use a chlorine bleach solution or a disinfectant that is effective against noroviruses.

Use caution when traveling. If you’re traveling to areas with a high risk of norovirus infection, consider eating only cooked foods, drinking only hot or carbonated beverages, and avoiding food sold by street vendors. Avoid traveling until 2 to 3 days after your symptoms are gone.