According to the Centers for Disease Control and Prevention (CDC), noroviruses cause 19-21 million infections, 56,000-71,000 hospitalizations, and 570-800 deaths every year in the United States.
Although noroviruses more commonly strike during the winter months, they can appear at any time of the year.
Here are some key points about norovirus. More detail and supporting information is in the main article.
- Around 90 percent of non-bacterial cases of gastroenteritis worldwide are believed to be caused by noroviruses.
- Although known as the winter vomiting bug, norovirus can strike at any time of year.
- Norovirus outbreaks are more likely to occur in crowded or closed communities.
- The most common cause of norovirus is believed to be contaminated food.
- Simple measures of personal and food hygiene can substantially reduce norovirus transmission.
What is norovirus?
The majority of non-bacterial outbreaks of gastroenteritis are attributable to noroviruses.
Noroviruses include Norwalk, Snow Mountain, and Hawaii viruses. Approximately 90 percent of all non-bacterial outbreaks of gastroenteritis are believed to be caused by noroviruses globally.
Noroviruses are shed in the feces (stools) and vomit of infected people and animals.
The infection can be transmitted by:
- consuming contaminated foods
- drinking contaminated water
- touching an infected person with your hand and then touching your mouth
- touching a contaminated surface with your hand and then touching your mouth
It is not easy to eliminate noroviruses because they can survive in both hot and cold temperatures, and are resistant to many disinfectants.
As noroviruses undergo genetic changes all the time, humans tend to become infected more than once during their lifetimes. Normally, if you have recurring infections, symptoms are less severe each time.
Norovirus infection outbreaks are more likely to occur in crowded or closed communities, such as cruise ships, long-term care facilities, prisons, overnight camps, and dormitories - places where the virus can spread rapidly from human-to-human.
Nausea, vomiting and abdominal pain are typical symptoms of norovirus infection.
Typical norovirus symptoms include:
- nausea - usually the first symptom
- vomiting - sometimes violent and sudden
- stomachache (abdominal pain)
- abdominal cramps
- watery or loose diarrhea
- feeling unwell and lethargic (malaise)
- fever and chills, usually mild
- myalgias (body aches)
During the brief period when symptoms are present people can feel very ill and vomit, often violently without warning, many times a day.
Signs and symptoms, which usually last from 1-3 days, appear about 24-48 hours after initial infection - in some cases, the incubation period may only be 12 hours. Sometimes, the diarrhea can last longer than 3 days.
According to the Centers for Disease Control and Prevention (CDC), the virus can be in the stool and vomit of an infected person from the day they start to feel ill to as long as 2 weeks after they feel better.
Norovirus treatments and risk factors
No specific therapy exists for norovirus gastroenteritis, so management is primarily to prevent dehydration and provide symptom control.
Experts say that fasting will not speed up recovery. Therefore, patients should eat a light diet with foods that are easy to digest, such as rice, bread, soups, or pasta. Babies should be given what they would usually eat.
It is important to replace the fluids that are lost through vomiting or diarrhea, especially with very young children and elderly people.
The speed of dehydration can be sudden and in some cases life-threatening. Young children and elderly patients are particularly susceptible to dehydration, which means dehydration is an important component to look out for, because the symptoms occur so abruptly. Patients who are not able to drink enough liquids may need to receive fluids intravenously.
The following risk factors may increase a person's likelihood of becoming infected with the norovirus:
- Weakened immune system - people whose immune systems are impaired, such as organ transplant recipients or individuals with AIDS have a higher risk of becoming infected and developing symptoms.
- Food hygiene - living in a house where food hygiene procedures are not correctly observed can result in infection.
- Children - living with a child who goes to a childcare center or attends preschool can increase the risk of infection.
- Accommodation - staying in hotels, cruise ships, vacation resorts where there are lots of people together increases the risk of infection.
- Isolated living arrangements - living in closed or semi-closed communities, such as nursing homes, hospitals, or retirement centers can make infection more likely.
After being infected with a norovirus, people have temporary immune protection, which usually lasts no more than 14 weeks.
Causes of norovirus
The U.S. Department of Health and Human Services informs that the most common causes of human norovirus infections are:
- contaminated foods
- ready-to-eat foods that were handled by infected workers (salads, ice, cookies, fruit, and sandwiches)
- any food contaminated with the feces or vomit of an infected person
The norovirus can spread via human contact with an infected person, through contact with contaminated surfaces or objects, or by consuming contaminated water or food.
Norovirus outbreak risks
According to the CDC, the majority of foodborne norovirus infection outbreaks most likely arise through direct contamination of food by an infected handler immediately before its consumption.
Outbreaks have often been linked to cold food consumption, including salads, sandwiches and bakery products. Such liquid items as salad dressing or cake icing have also been implicated as outbreak causes. Sometimes, oysters from contaminated waters have been linked to widespread gastroenteritis outbreaks.
Waterborne outbreaks of norovirus infection in community settings have commonly been caused by sewage contamination of wells and recreational water, says the CDC.
People infected with norovirus should stay at home to avoid contaminating surfaces in public places.
The best way to prevent the spread of foodborne noroviruses is to practice proper food handling. Good hand hygiene and food cleaning are important to prevent transmission of norovirus.
Noroviruses can survive freezing, as well as temperatures as high as 140° F (60° C). Some people may even become infected after eating steamed shellfish. Noroviruses can survive up to 10 parts per million chlorine, levels much higher than that found in current public water systems.
In spite of these features, experts say that relatively simple measures of personal and food hygiene substantially reduce foodborne transmission of noroviruses.
The following steps are known to reduce the risk of norovirus infection:
- Handwashing - washing hands frequently and thoroughly with soap and warm water, especially after going to the toilet, changing a diaper, and before preparing meals.
- Cleaning surfaces - preferably with a bleach-based household cleaner. When possible, let the bleach remain on the surface for about 10 minutes. Infected people may often vomit violently, without warning (the vomit is infectious). Any surfaces near the vomit should be thoroughly cleaned promptly.
- Raw foods and food in general - avoiding shellfish that may have come from contaminated waters and any foods that may have been prepared by someone who was sick should be thrown out. Fruits and vegetables should be washed and scrubbed thoroughly.
- Infected feces and vomit - make sure they are flushed away and clean the surrounding toilet area immediately with a bleach-based household cleaner.
- Clothing and bed clothes - if they could have become contaminated, wash with hot soapy water.
- Keep the toilet seat down - when flushing a toilet, keeping the toilet seat down can prevent infectious microbes from entering the air.
- If infected - stay at home, especially for patients whose job requires handling food.
- Disposable towels - if you are especially vulnerable to infection, e.g. you are caring for an infected person, use disposable paper towels to dry you hands rather than cloth ones; the virus may survive for some time on objects.
- Healthcare facilities - for example, hospitals should focus on methods to limit transmission by isolating patients.
- Traveling - those traveling to where sanitation is suspect should only drink bottled water, even for brushing teeth. In addition, it is advisable to avoid buffets and uncooked foods.
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:
Some people are unable to drink enough liquids to replace those lost through vomiting or diarrhea, and may become dehydrated and require special medical attention. Young children, the elderly, and individuals of any age who are unable to take care of themselves are especially vulnerable.
Examples of oral rehydration fluids (ORF) include: Infalyte, Kao Lectrolyte, Naturalyte, Oralyte, and Pedialyte.