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National Infectious Disease Surveillance Center
Information for families and ordinary citizens

Norovirus, which causes vomiting, diarrhea and other forms of gastrointestinal distress, becomes especially common between November and April. This viral infection spreads rapidly from person to person, and outbreaks have occured at pre-schools, kindergartens, elementary schools and other institutions where a large number of children interact in a small amount of space for an extended period of time.

Norovirus is well known as a cause of food poisoning in individuals who consume shellfish. However, the majority of outbreaks at pre-schools, kindergartens and elementary schools involve person to person transmission that begins with a single individual. This kind of transmission is extremely effective at spreading the virus. While it is impossible to completely prevent the spread of norovirus during peak season, there are ways to minimize the risk of outbreaks. Please read the following to increase your awareness of norovirus symptoms and ways you can help prevent norovirus from spreading.

１》    Norovirus symptoms and treatment
①    Symptoms：
The primary symptoms of Norovirus are nausea, vomiting and diarrhea. Norovirus does not normally cause blood in the stool. While fever is a possible symptom, extremely high fevers are uncommon in norovirus cases. Vomiting is especially common in young children that contract norovirus, and children with norovirus may experience vomiting or diarrhea up to 10 times a day in extreme cases. The incubation period (the period between infection and the onset of symptoms) for norovirus is short, ranging from several hours to an average of 1-2 days. Individuals that contract norovirus typically experience symptoms for an average of 1-2 days.

Although norovirus does not require extended hospitalization, even for individuals with other medical conditions or weakened immune systems, please be aware that, in extremely rare cases, it is possible for individuals with norovirus to choke as a result of vomit entering the throat.

②    Treatment：
There is no panacea for treating norovirus symptoms. The most important thing during the period when an individual experiences norovirus symptoms is hydration. In extreme cases, an individual with norovirus may have to be hydrated intravenously. Antibiotics are not used to treat norovirus, as they have no effect and may prolong diarrhea symptoms. The most common treatment for norovirus is medicine that suppresses vomiting and other gastrointestinal symptoms. If diarrhea persists, doctors may recommend antidiarrhetic medication, but such medication should not be used when symptoms first appear.

２》 Prevention
There is no vaccine for norovirus and transmission, especially among children and the elderly, is somewhat difficult to prevent. The most effective way to prevent norovirus transmission is hand washing with soap and water. Other prevention methods are listed below.

However, please be aware that exposure to norovirus is common during norovirus season and that allowing children to attend school with symptoms can cause the infection to spread between households and across a region.

①    Food Preparation and Serving：
Norovirus can be contained in the stool of an infected individual even if the individual does not exhibit any noticeable symptoms (this is known as “subclinical infection”). It is possible for parents, guardians or other adults to transmit the virus to children unknowingly. Please be aware of the following to prevent transmission while preparing and serving food.

・Before and after cooking, wash hands thoroughly with soap and water (liquid soap is recommended).
・When cooking shellfish in the shell, be sure to cook the shellfish thoroughly. Immediately use boiling water to disinfect knives and cutting boards used to prepare shellfish.
・It is recommended to wash hands before serving food. This is critical for individuals experiencing diarrhea or vomiting.

②    Disposing of vomit and loose stool：
Vomit and stool of infected individuals contain large amounts of norovirus pathogens. It only takes a small amount of the virus to infect another person. Disinfecting surfaces contaminated with norovirus requires chlorine-based (common brands include Milton and Purelox) or bleach-based cleaners (common brands include Haita), as other cleaners are ineffective for this purpose. Vomit and stool of individuals that have contracted norovirus should be handled with caution.

３》Advice for families
Norovirus transmission often occurs in the home, even if the onset of symptoms occurs at school, work or other institution. Young children and the elderly are particularly vulnerable to norovirus. Please keep the following in mind in your home.

①    Hand washing (with soap and water) is the most important way to prevent norovirus transmission. Make sure that every member of the family washes their hands after returning home and before meals.
②    Norovirus can be transmitted via consumption of raw shellfish. It is recommended that young children and elderly avoid consuming shellfish due to their increased risk.
③    Wash hands thoroughly with soap and water before preparing or serving food.
④    Use hypochlorite based cleaner (concentration of 200 ppm or above, or in the case of household bleach dilute 1 part bleach with 200 parts water) to disinfect clothing, objects and areas contaminated with norovirus.

※Do not use hypochlorite or bleach based cleaners to disinfect the次body or hands.

For more information on norovirus, please visit the website below.
http://www.mhlw.go.jp/topics/syokuchu/kanren/yobou/040204-1.html