CDC Answers Your Questions About

Noroviruses: Q&A

What are noroviruses?

Noroviruses are a group of viruses that cause the “stomach flu,” or gastroenteritis (GAS-tro-enter-I-tis), in people. The term norovirus was recently approved as the official name for this groupof viruses. Several other names have been used for noroviruses, including:

·  Norwalk-like viruses (NLVs)

·  caliciviruses (because they belong to the virus family Caliciviridae)

·  small round structured viruses.

Viruses are very different from bacteria and parasites, some of which can cause illnesses similarto norvirus infection. Viruses are much smaller, are not affected by treatment with antibiotics, andcannot grow outside of a person’s body.

What are the symptoms of illness caused by noroviruses?

The symptoms of norovirus illness usually include nausea, vomiting, diarrhea, and some stomachcramping. Sometimes people additionally have a low-grade fever, chills, headache, muscleaches, and a general sense of tiredness. The illness often begins suddenly, and the infectedperson may feel very sick. The illness is usually brief, with symptoms lasting only about 1 or 2days. In general, children experience more vomiting than adults. Most people with norovirusillness have both of these symptoms.

What is the name of the illness caused by noroviruses?

Illness caused by norovirus infection has several names, including:

·  stomach flu – this “stomach flu” is not related to the flu (or influenza), which is arespiratory illness caused by influenza virus.

·  viral gastroenteritis – the most common name for illness caused by norovirus.Gastroenteritis refers to an inflammation of the stomach and intestines.

·  acute gastroenteritis

·  non-bacterial gastroenteritis

·  food poisoning (although there are other causes of food poisoning)

·  calicivirus infection

How serious is norovirus disease?

Norovirus disease is usually not serious, although people may feel very sick and vomit manytimes a day. Most people get better within 1 or 2 days, and they have no long-term health effectsrelated to their illness. However, sometimes people are unable to drink enough liquids to replacethe liquids they lost because of vomiting and diarrhea. These persons can become dehydrated andmay need special medical attention. This problem with dehydration is usually only seen amongthe very young, the elderly, and persons with weakened immune systems. There is no evidence tosuggest that an infected person can become a long-term carrier of norovirus.

How do people become infected with noroviruses?

Noroviruses are found in the stool or vomit of infected people. People can become infected withthe virus in several ways, including:

·  eating food (see food handler fact sheet) or drinking liquids that are contaminated withnorovirus;

·  touching surfaces or objects contaminated with norovirus, and then placing their hand intheir mouth;

·  having direct contact with another person who is infected and showing symptoms (forexample, when caring for someone with illness, or sharing foods or eating utensils withsomeone who is ill).

Persons working in day-care centers or nursing homes should pay special attention to children orresidents who have norovirus illness. This virus is very contagious and can spread rapidlythroughout such environments.

When do symptoms appear?

Symptoms of norovirus illness usually begin about 24 to 48 hours after ingestion of the virus, butthey can appear as early as 12 hours after exposure.

Are noroviruses contagious?

Noroviruses are very contagious and can spread easily from person to person. Both stool andvomit are infectious. Particular care should be taken with young children in diapers who mayhave diarrhea.

How long are people contagious?

People infected with norovirus are contagious from the moment they begin feeling ill to at least 3days after recovery. Some people may be contagious for as long as 2 weeks after recovery.Therefore, it is particularly important for people to use good handwashing and other hygienicpractices after they have recently recovered from norovirus illness.

Who gets norovirus infection?

Anyone can become infected with these viruses. There are many different strains of norovirus,which makes it difficult for a person’s body to develop long-lasting immunity. Therefore,norovirus illness can recur throughout a person’s lifetime. In addition, because of differences ingenetic factors, some people are more likely to become infected and develop more severe illnessthan others.

What treatment is available for people with norovirus infection?

Currently, there is no antiviral medication that works against norovirus and there is no vaccine toprevent infection. Norovirus infection cannot be treated with antibiotics. This is becauseantibiotics work to fight bacteria and not viruses.

Norovirus illness is usually brief in healthy individuals. When people are ill with vomiting anddiarrhea, they should drink plenty of fluids to prevent dehydration. Dehydration among youngchildren, the elderly, the sick, can be common, and it is the most serious health effect that canresult from norovirus infection. By drinking oral rehydration fluids (ORF), juice, or water,people can reduce their chance of becoming dehydrated. Sports drinks do not replace thenutrients and minerals lost during this illness.

Can norovirus infections be prevented?

Yes. You can decrease your chance of coming in contact with noroviruses by following thesepreventive steps:

·  Frequently wash your hands, especially after toilet visits and changing diapers and beforeeating or preparing food.

·  Carefully wash fruits and vegetables, and steam oysters before eating them.

·  Thoroughly clean and disinfect contaminated surfaces immediately after an episode ofillness by using a bleach-based household cleaner.

·  Immediately remove and wash clothing or linens that may be contaminated with virusafter an episode of illness (use hot water and soap).

·  Flush or discard any vomitus and/or stool in the toilet and make sure that the surroundingarea is kept clean.

Persons who are infected with norovirus should not prepare food while they have symptoms andfor 3 days after they recover from their illness (see food handler information sheet). Food thatmay have been contaminated by an ill person should be disposed of properly.

Influenza

Influenza, or “the flu”, is a contagious respiratory illness caused by an influenza virus (type A or B).  The illness is characterized by a variety of symptoms that can include fever, headache, sore throat, nasal congestion, dry cough, fatigue and muscle aches.  Some people may also have associated gastrointestinal symptoms such as nausea, vomiting and diarrhea.  Young children, the elderly and people with certain underlying medical conditions (such as asthma, chronic lung disease, diabetes and heart disease) are particularly susceptible to influenza and its complications, most notably pneumonia and respiratory failure.  Each year, 5-15 % of the world population comes down with the flu.  3-5 million people develop severe flu-related illness and 250-500 thousand deaths occur worldwide from influenza-related complications.

Influenza viruses are spread via respiratory droplets from coughing and sneezing.  Direct person-to-person contact is the major mode of transmission for the flu, but indirect contact via the touching of contaminated environmental surfaces (and then touching your nose, mouth or eyes) can also lead to influenza infection.  After becoming infected by the virus, most people will show symptoms within 2-5 days.  The treatment for most people with the flu is rest, fluids and acetaminophen (Tylenol) or ibuprofen (Advil/Motrin) for the fever, headache and body aches.  The acute illness typically lasts for less than a week.  People infected with the influenza virus can be contagious from the day prior to the onset of symptoms up to 5 days after their illness begins.

The primary method of flu prevention is annual immunization against the particular strains of influenza that are predicted to be prevalent that year.  The most widely used method for immunization is the “flu shot”.  This is an inactivated (killed virus) vaccine that is developed based upon input from worldwide medical authorities to address the influenza (types A and B) threat for a particular flu season.  It can be used in people older than 6 months of age, both those who are healthy and those with chronic medical conditions.  An alternative to the injectable vaccine is a nasal spray vaccine that is made with live, weakened viruses (LAIV or Live Attenuated Influenza Vaccine) that do not cause the flu.  It can be used in healthy people from age 5 to 49 years who are not pregnant.

The flu season in the United States and much of the Northern Hemisphere is October to May with the peak incidence for influenza running from December through March.  It takes about 2 weeks after flu vaccination for your immune system to develop adequate protection against the influenza virus.  Therefore, it is recommended that people get vaccinated in October or November near the beginning of the flu season, though later vaccination can also help to avoid getting the flu as the season progresses. 

It is important for the international traveler to realize that the flu season in the Southern Hemisphere runs from April to September (the Fall and Winter months) and that the influenza viruses for the season (as well as those used in the formation of the flu vaccine) may differ from those in the Northern Hemisphere.

In addition to an annual influenza vaccination, there are several other measures that people can utilize to lessen the likelihood of coming down with the flu.  In the event of a local or widespread flu outbreak, try to avoid contact with individuals who are sick as well as large crowds.  Cleaning your hands frequently throughout the day with soap and water or an alcohol-based hand sanitizer and being careful not to touch your eyes, nose and mouth will help to limit the chances of picking up the influenza virus from a contaminated surface.  Disinfection of contact surfaces (such as countertops, tables, telephones, door handles, faucets) in the home, schools, the workplace and other public areas can decrease the transmission of the virus.  Should you develop symptoms of the flu, it’s important to minimize the chances of spreading the virus to others by staying home while ill, avoiding close contact with others and remembering to cover your mouth and nose while coughing and sneezing.

Antiviral drugs are available for both prevention and treatment of the flu.  Amantadine, rimantadine and oseltamivir (Tamiflu) are approved for prevention of the flu and can be taken for 2 weeks or more during influenza outbreaks.  Amantadine, rimantadine, oseltamivir and zanamivir (Relenza) may be prescribed to people who are diagnosed with influenza.  The medications should be started within 2 days of becoming ill and then continued for 3-5 days.  They can reduce flu symptoms, shorten the length of your illness and help to make you less contagious to others.  Oseltamivir and zanamivir are effective against both influenza type A and type B.  Amantadine and rimantadine are effective only against influenza A.

Avian Influenza (Bird Flu) A H5N1 – An Emerging Health Concern

Avian influenza (bird flu) viruses are found in a variety of bird populations worldwide.  Wild birds are often asymptomatic carriers of the virus whereas domesticated birds such as chickens, ducks and turkeys can be highly susceptible to the viruses.  The resulting infection can range from mild symptoms to severe illness and death.  The infected birds shed the virus in their saliva, nasal secretions and droppings which can then be passed on to other birds either by direct contact or via contaminated surfaces, food and water.  The more virulent outbreaks can result in near total mortality of a flock within a couple of days.

Avian influenza A H5N1 is a particular subtype of bird flu virus that emerged in Hong Kong in 1997 and then resurfaced in several Asian domestic bird flocks in 2003.  Since then, more than 100 million birds have either died from the virus or were destroyed in an attempt to contain the outbreaks and spread of the illness.

It is unusual for avian influenza viruses to infect humans.  However, since 1997 more than 150 human cases of avian influenza A H5N1 infection have been reported, with an overall mortality rate of 50%.  Most of these cases were felt to be due to direct contact with infected domesticated birds or surfaces contaminated with their secretions and droppings, but rare cases of direct person-to-person transmission have also occurred.

A major concern regarding the avian influenza A H5N1 virus is that it could mutate and gain the ability to be passed directly from person to person.  Since this would result in a foreign influenza virus subtype being introduced into the world population, humans would have little or no natural immunity to the virus.  This in turn could result in seasonal epidemics and potentially an influenza pandemic (worldwide outbreak) such as those experienced in 1918, 1957 and 1968 that involved newly-introduced avian influenza virus subtypes.

Various international public health organizations, such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO), are closely monitoring the avian influenza outbreaks, particularly those that involve human victims.  Governments are developing pandemic influenza disaster programs that include enhanced vaccine production protocols, increasing the manufacture of antiviral medications (oseltamivir and zanamivir) that appear to be effective against the avian influenza A H5N1 virus, and revising quarantine guidelines.

Most travel health authorities have not yet recommended restrictions for travel to countries currently experiencing outbreaks of avian influenza A H5N1 in domestic bird flocks.  However, they do recommend that travelers avoid poultry farms, live animal markets and other direct contact with domestic and wild birds.  All poultry food products, including eggs, should be thoroughly cooked prior to consumption.  In addition, general influenza prevention guidelines, especially frequent hand washing, should be practiced whenever traveling during the flu season or to countries where there is a risk of being exposed to the avian influenza virus.  If you develop symptoms of the flu (fever, cough, sore throat, headache, body aches) while traveling in a region of the world with reported bird flu outbreaks or within 10 days of visiting the area, you should be evaluated by a health care provider to determine the cause of your illness and the appropriate treatment.

Additional information and updates regarding the current flu season, avian influenza A H5N1 and general international travel health recommendations are available at the CDC (www.cdc.gov) and WHO (www.who.int) web sites.