What Is Norovirus Infection? What Causes Norovirus Infection?

Noroviruses, also known as Norwalk-like viruses, SRSV (small round structured viruses, are part of a group of viruses from the family Caliciviridae that are the most common cause of stomach upset (gastroenteritis) in the USA, Great Britain and Western Europe; about 90% of epidemic non-bacterial outbreaks of gastroenteritis around the world. Sometimes referred to as winter vomiting disease, norovirus infection often affects people during the winter months. However, people may be affected at any time of year.

After a person has a norovirus infection, immunity is only temporary - about 14 weeks - and usually incomplete. Individuals with blood type O are more susceptible to infection, while those with types B and AB are partially protected. Given the genetic variability of noroviruses, individuals are likely to be repeatedly infected throughout their lifetimes. However, experts say that having recurring infections does eventually provide some protection from future infection.

Norovirus infection outbreaks more commonly occur in closed or semi-closed communities, such as prisons, dormitories, cruise ships, schools, long-term care facilities and overnight camps - places where infection can spread rapidly from human-to-human or through tainted food and surfaces. Infection outbreaks may also occur from food that was handled by an infected person.

According to the Centers for Disease Control and Prevention (CDC) it is estimated that at least 50% of all foodborne outbreaks of gastroenteritis can be attributed to noroviruses. The National Health Service (NHS), UK, estimates that approximately between 600,000 and 1,000,000 British people every year are infected.

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.

According to the CDC, USA, 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.

According to Medilexicon's medical dictionary:

Caliciviridae is "A family of naked icosahedral single-stranded positive sense RNA viruses 30-38 mm in diameter associated with epidemic viral gastroenteritis and certain forms of hepatitis in humans."

What are the signs and symptoms of a norovirus infection?

A symptom is something the patient feels and reports, while a sign is something other people, such as the doctor detect. For example, pain may be a symptom while a rash may be a sign.

Norovirus infection causes gastroenteritis - inflammation of the stomach and the small and large intestines.

Norovirus infection signs and symptoms include:

• Nausea - usually the first symptom
• Vomiting - sometimes violent and sudden
• Stomachache (abdominal pain)
• Abdominal cramps
• Watery or loose diarrhea
• Weight loss
• Generally feeling unwell and lethargic (malaise)
• Fever/chills, usually mild
• Aching limbs
• Headache
• In rare cases patients may lose their sense of taste

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 generally last from one to three days usually appear about 24 to 48 hours after initial infection (incubation period of 24 to 48 hours) - in some cases the incubation period may only be 12 hours. Sometimes the diarrhea can last longer than three days.

An individual's feces (stools) may still have noroviruses for some time after they have recovered. According to the CDC, USA, the virus can be in the stool and vomit of infected persons from the day they start to feel ill to as long as 2 weeks after they feel better.

It is possible to be infected and have no signs or symptoms. In such cases, the person is contagious (can pass it on to other people).

Diagnosing norovirus infection

In the vast majority of cases diagnosis is based on the patient's signs and symptoms alone. The norovirus can be identified by testing a stool sample

Treatment for norovirus infection

Doctors tend to let the norovirus infection run its course. No specific therapy exists for norovirus gastroenteritis.

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 normally eat.

It is important to replace the fluids that are lost through vomiting and/or diarrhea, especially with very young children and elderly people. Young children and elderly patients are particularly susceptible to dehydration. Patients who are not able to drink enough liquids may need to receive fluids intravenously.

What are the risk factors for norovirus infection?

A risk factor is something which increases the likelihood of developing a condition or disease. For example, obesity significantly raises the risk of developing diabetes type 2. Therefore, obesity is a risk factor for diabetes type 2. The following risk factors may increase a person's risk 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.
• Living in a house where food hygiene procedures are not properly observed
• Living with a child who goes to a child care center or attends preschool
• Staying in hotels, cruise ships, vacation resorts where there are lots of people together
• Living in in closed or semi-closed communities, such as nursing homes, hospitals or retirement centers

What are the causes of norovirus infection?

Noroviruses are shed in the feces (stools) and vomit of infected people and animals.

The infection can be transmitted by:

• Consuming contaminated foods
• Consuming 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. Food and drinks can become contaminated with norovirus very easily because the virus is very small, and also because it probably takes fewer than 100 norovirus particles to make a person ill.

What are the possible complications of norovirus infection?

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:

• Dehydration
• Malnutrition

Some people are unable to drink enough liquids to replace those lost through vomiting and/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. A double-blind trial of oral rehydration solutions for children with diarrhea and vomiting related to acute viral gastroenteritis found that Gatorade is as effective as Pedialyte in correcting dehydration and improving bowel symptoms.

Prevention of norovirus infection

Methods of prevention of the spread of foodborne noroviruses is based on the provision of safe food and water. Noroviruses can survive freezing, as well as temperatures as high as 60C (140F). Some people may even become infected after eating steamed shellfish. Noroviruses can survive up to 10 ppm chlorine, levels much higher than that found in current public water systems.

In spite of these features, experts say that fairly simple measures of personal and food hygiene substantially reduce foodborne transmission of noroviruses.

The following steps are known to considerably reduce the risk of norovirus infection:

• Handwashing - wash your hands frequently and thoroughly with soap and warm water, especially after going to the toilet, changing a diaper (UK: nappy), and before preparing meals.
• Possibly contaminated surfaces - clean them with disinfectant, preferably a bleach-based household cleaner. It is important to heed the instructions that go with the product. When possible, let the bleach remain on the surface for about ten 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 - if you are going to eat raw foods make sure they are from a reliable source. Avoid shellfish that may have come from contaminated waters. If you steam oysters your chances of becoming infected are significantly reduced.
  
  Any foods that may have been prepared by someone who was sick should be thrown out. Carefully wash fruit and vegetables.
• 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.
• If you are infected - stay at home, especially if your job involves 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.
• Travelling - if you are travelling abroad, and sanitation is suspect, only drink bottled water, even for brushing your teeth. Avoid buffets and uncooked foods.
• Disinfecting drinking water - if you suspect your water may be contaminated it is possible to disinfect it before consumption:
  
  
  • Boiling - a full boil should last for at least one minute (one minute bubbling). If you are over 2,000 meters altitude (6,500 feet) the water should be boiled for an additional minute.
  • Iodine - if possible, warm the water to 20C, add in the iodine, mix it, and let it stand for at least 20 minutes. If the water is colder let it stand for 40 minutes. Follow the manufacturer's instructions regarding how much to use.
    
    Pregnant women should not use iodine drops to purify water. Do not use iodine to disinfect water for long periods as there is a risk of thyroid gland problems.