Facts About Norovirus and Norovirus Disease

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Norovirus and Norovirus Disease

Norovirus is a highly contagious virus. It is sometimes called the "winter vomiting bug" in the UK and is a common virus which is usually prevalent in winter time and causes gastritis and colitis. There are many different strains of norovirus and the immunity acquired by a past infection may not work for different types. That means in a season when a new strain is prevalent, you may be infected with it even if you have suffered from norovirus in the past. We advise you to be careful of a new norovirus strain which is prevalent every year in Japan.

Infection Route of Norovirus

Active norovirus exists in the feces and vomit of a virus carrier. Because it ends up in waterways via the sewer system, the fact that the virus is found in rivers, especially in big cities, is not surprising. As a result, the virus accumulates in aquatic life such as shellfish (especially oysters). Therefore, eating raw shellfish in a prevalent season is one of risks of its infection.

Furthermore, kitchen utensils and water used with contaminated shellfish could also become contaminated with the virus. This means that other food items in the kitchen could also be contaminated. Norovirus infection may occur by eating these items, even if it is not raw shellfish.

When your fingers are contaminated with norovirus, it can enter the body via your mouth, establishing the infection. Because norovirus can be found in the feces of a virus carrier, he/she may carry the virus on their fingers after using the lavatory. The norovirus can be washed off through proper hand washing. However, if the carrier do not wash his/her hands sufficiently and/or properly, the virus may still be present on his/her fingers. If the carrier touches the surfaces of various objects with the contaminated hand, the surface is also contaminated, and the virus can be transmitted to another person who touches those surfaces.

Norovirus can be found in the vomit of a virus carrier and can continue to survive in dried vomit causing the virus to become airborne. This can infect other people when the virus is ingested through the mouth.

Clinical Course of Norovirus Disease

The most obvious symptoms of norovirus disease are diarrhea and nausea/vomiting (throwing up). They are usually associated with stomach pain, headache, and fever. These symptoms develop 12-48 hours after being exposed to the virus and disappear 1 to 3 days after the onset of symptoms. Sometimes when vomiting and diarrhea are severe, dehydration may develop.

Treatment for Norovirus Disease

No specific treatments are available for norovirus infections. Take a lot of water containing salt to prevent dehydration due to vomiting and diarrhea. It is recommended to take sports drinks or oral rehydration fluids. The latter can be bought at a pharmacy without a prescription. In case of severe dehydration, hospitalization may be necessary. An anti-nausea drug, such as domperidone may be effective for nausea/vomiting caused by norovirus disease. If you are not able to take an oral tablet because of vomiting, it is available in suppository form at medical clinics. You can ask for domperidone at the Health Center on each campus of Keio University, but only the tablet form is available.

Prevention of Norovirus Infection

Hands infected with norovirus can be cleaned by washing them properly with soap and water. Thus, washing your hands before eating and cooking is very important in the prevention of norovirus infection.

Food that has come into contact with shellfish contaminated with norovirus may also be contaminated. Thus, all food and the sink in which they are cleaned or prepared should also be washed thoroughly with tap water.

Norovirus can be killed by sufficient heating, for example, at 100OC for more than 3 minutes. Although raw oysters are delicious, it is recommended to sufficiently fry or boil them at least during seasons when norovirus is prevalent. Be aware that norovirus resists heat rather well--just pouring boiling water over it is not enough to kill the virus.

When you are suffering from norovirus disease, it is necessary for you to pay attention to prevent spreading it to others. Wash your hands well, especially after using the lavatory. Avoid preparing food and avoid contact with other persons as much as possible. It is better for you to be isolated from children, old persons, and sick persons. It is a good idea to use disposable eating utensils. Be aware that norovirus may continue to exist in a patient's feces for up to 2 weeks after infection even when he/she is free from any symptoms. Thus, please continue to wash your hands well even after you recover from the disease.

Because alcohol (ethanol) is not effective in killing norovirus, a sprinkling of alcohol is NOT an effective disinfectant of norovirus. Instead of alcohol, use a sodium hydrochloride solution as a sanitizer. A 0.02% solution* is recommended for sanitizing toilet seats, doorknobs, desks, etc. Wipe them with a cloth or tissue which has been soaked in the solution. In terms of kitchen utensils, you can soak them in the solution for a while and washed thoroughly with tap water after the treatment.

Because vomit from a norovirus carrier is a source of norovirus infection, it must be cleaned as soon as possible. Furthermore, after cleaning it up, the surfaces that come into contact with it should be treated with a 0.1-0.5% sodium hydrochloride solution* to totally kill the virus.

*You can buy a bottle of bleaching agent such as "Kitchen Haiter," a 5% sodium hydrochloride solution, at a pharmacy. To make a 0.02% sodium hydrochloride solution, fill a 500 ml pet bottle with tap water and add 2 ml of Kitchen Haiter. To make a 0.1% solution, add 10 ml of Kitchen Haiter to 500 ml of tap water.

In case that you are diagnosed as being infected with norovirus

If you are diagnosed with norovirus at a medical institution including the Keio University Health Centers, you are prohibited from attending classes until symptoms disappear. This is a measure to prevent spreading the infection to other students on campus. Before you attend classes again, you should stop by the Health Center and get permission from a doctor at the Center.