What to know about norovirus

Also known as the winter vomiting bug, norovirus is a common cause of sickness, diarrhea, and gastroenteritis.

Norovirus is causing gastroenteritis in 19–21 million people per year in the United States, according to the Centers for Disease Control and Prevention (CDC). The virus also accounts for 56,000–71,000 annual hospitalizations and 570–800 deaths each year in the US.

While norovirus causes infection more frequently during the winter months, it can affect people any time of year.

People often misinterpret a norovirus infection as “stomach flu.” Gastroenteritis is the medical term, and it has no link with flu which is a respiratory infection.

We describe the signs and causes of norovirus in this article, and explain how to treat and prevent infection.

What is norovirus?

Norovirus is a member of the Virus family Caliciviridae. These viruses are responsible for around 90 percent of outbreaks of viral gastroenteritis, and about 50 percent of cases worldwide.

Norovirus has the infection circulating in the urine and vomiting of humans and animals. Individuals will contract the virus by following:

• consuming contaminated foods
• drinking contaminated water
• touching their mouth with the same hand that they just used to touch someone who has norovirus or a contaminated surface

Because they can survive in hot and cold temperatures, and they are resistant to many disinfectants, eliminating noroviruses can be hard.

Noroviruses undergo continuous genetic alterations. For this reason, during their lifetime, humans tend to develop a norovirus infection more than once although the symptoms are usually less severe each time.

Symptoms

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
• headaches

People can feel extremely sick and vomit several times a day, often violently and without notice, during the brief period when symptoms are present.

The CDC reports that signs and symptoms usually last 1–3 days, and occur after the initial infection between 12 and 48 hours. Diarrhea can in some cases last longer than 3 days.

It is important to note that the virus can still spread through the stool and vomit 2 weeks after the symptoms have resolved.

Treatment

There is no specific treatment for noroviral gastroenteritis. Doctors, instead, aim to prevent the symptoms of dehydration and control.

Fasting doesn’t speed recovery. People with norovirus should eat a light diet that consists of easily digestible foods, such as rice, bread, soups, and pasta. Norovirus infants will continue to take their regular diet.

A person will need to make sure that the fluids they lose through vomiting or diarrhea are replaced. It is especially important to replace fluids in very young children and older adults, as people in those age groups are particularly susceptible to very rapid dehydration.

Certain people may find taking oral rehydration fluids helpful. The products available include Infalyte, Kao Lectrolyte, Naturalyte, Oralyte, and Pedialyte, among others.

Dehydration can be abrupt, and life threatening to some persons. People with dehydration who can’t drink enough fluids intravenously may need to obtain fluids.

Risk factors

The following risk factors can increase the likelihood that a individual will get infected with the norovirus:

• having a weakened immune system, for example, people who have undergone an organ transplant and individuals living with HIV
• living in a household whose members do not correctly observe food hygiene practices
• living with a child who attends a child care center or preschool
• staying in a hotel, cruise ship, or vacation resort where many people congregate
• living in a closed or semi-closed community, such as a nursing home, hospital, or retirement center

People have temporary immunity from further infection after a norovirus infection, although this typically only lasts for 2–3 years.

Causes

The Department of Health and Human Services states the most common causes of human norovirus infections are as follows:

• contaminated foods
• shellfish
• ready-to-eat foods, such as salads, ice, cookies, fruit, and sandwiches, that a worker with a norovirus infection has handled
• any food that contains particles of the feces or vomit of a person with norovirus

Outbreak risk factors

According to the CDC, about 70 percent of outbreaks of foodborne norovirus infection occur due to the direct contamination of the food by a norovirus handler immediately prior to consumption.

Outbreaks have often had links to cold foods, including salads, sandwiches and products from bakeries.

Authorities have also involved liquid food items such as salad dressing and cake icing as causes for the outbreak.

Oysters from contaminated waters have sometimes taken blame for widespread outbreaks of gastroenteritis.

Sewage contamination of wells and recreational water in community settings has also caused waterborne outbreaks of norovirus infection.

Prevention

The best way to prevent foodborne noroviruses from spreading is to practice proper handling of the food. Good hand hygiene and food cleaning are key to preventing norovirus transmission.

Noroviruses can survive freezing temperatures, and temperatures up to 140 ° F or 60 ° C. After eating steamed shellfish some people may develop an infection even. Noroviruses can also survive in up to 10 parts of chlorine per million, levels that are much higher than those currently available in public water systems.

Despite these survival characteristics, experts say that relatively simple measures of personal and food hygiene can significantly reduce norovirus transmission from foodborne.

The following steps will reduce the risk of a person being infected with norovirus:

• Handwashing: Washing the hands with soap and warm water regularly and thoroughly may reduce the risk of infection, particularly after going to the bathroom or changing a diaper and before preparing meals.
• Cleaning surfaces: People should be washing ideally with a household cleaner focused on bleach. They should allow the bleach to stay on the surface for around 10 minutes, if possible. People with norovirus will often vomit violently, with no warning. They should immediately and thoroughly clean any surfaces near the vomit, since the vomit can be infectious.
• Avoiding risky foods: People should try to avoid shellfish that may have come from contaminated waters. They should also discard any foods that a person with norovirus may have prepared. People should thoroughly wash and scrub all fruits and vegetables.
• Removing infected feces and vomit: People need to ensure that they flush these away and clean the surrounding toilet area immediately with a bleach-based household cleaner.
• Washing clothing and bedclothes: If these items could have become contaminated, people should wash them with hot, soapy water.
• Keeping the toilet seat down: When flushing a toilet, people should keep the toilet seat down to prevent infectious microbes from entering the air.
• Staying at home: Eviting public contact will lower norovirus spread. This advice is especially relevant to people who have norovirus and are working in a job that requires them to handle food.
• Using disposable towels: Persons who are especially vulnerable to infection, such as those who care for an infected person, should dry their hands with disposable paper towels, rather than cloth towels. The virus will live on artifacts for some time.
• Taking care when traveling: People traveling to a location with a less developed sanitation system should use bottled water only, even for teeth brushing. The avoidance of buffets and uncooked foods is also recommended.

There is also a role for hospitals and other health care facilities in preventing transmission. They should focus on methods for limiting the virus’s spread, such as isolating people with an infection.

Complications

A norovirus infection clears itself in the vast majority of cases within a few days, and has no complications.

Less commonly, the following complications may occur:

• malnutrition
• constipation
• dyspepsia
• reflux

Some people can not drink enough fluids to replace the ones they lose from vomiting or diarrhea. They may become dehydrated, and need special medical treatment.

Particularly vulnerable are young children, older adults and people of any age who need a caregiver.