A Norovirus infection is a type of stomach ailment known as viral gastroenteritis. The infection is also commonly (and incorrectly) known as the stomach flu, and is not related to the respiratory symptoms caused by the influenza virus.
The infection is caused by Noroviruses, which have also been termed Norwalk-like viruses and calciviruses.
Noroviruses are named after the “Norwalk virus,” which was the cause of a gastroenteritis outbreak in a school in Norwalk, Ohio, in 1968. Once called Norwalk-like viruses, they have since been officially designated as Noroviruses.
An infection caused by a Norovirus is usually not life threatening, but can certainly cause a person to feel miserable. Typically, a person develops the symptoms of infection suddenly and becomes ill for several days. Vomiting and diarrhea occur many times during the illness; the loss of fluids can cause dehydration. Dehydration can be serious in infants, elderly people, and people whose immune systems are not functioning efficiently.
Recovery is usually complete, with no lingering symptoms or infection. However, as different strains (types) of the Norovirus exist, repeated gastrointestinal infections throughout a person's life are possible.
WORDS TO KNOW
GASTROENTERITIS: Gastroenteritis is an inflammation of the stomach and the intestines. More commonly, gastroenteritis is called the stomach flu.
Norovirus are found in the intestinal tract. A Norovirus infection can occur when fecal material is transferred to food, liquid, or an object; most often this occurs when food has been handled or an object like a doorknob is handled by someone who has not properly washed their hands after having had a bowel movement. The virus is ingested by eating the contaminated food or handling the object and then touching that hand to the mouth—this is called the fecal-oral route. A person becomes contagious from the moment they display symptoms to as long as two weeks after the symptoms have ended.
There is no evidence that the virus can by transferred by inhaling virus-laden air, even though it has been shown that vomiting does release virus particles into the air.
Norovirus infection is common. The United States Centers for Disease Control and Prevention (CDC) estimates that about 23 million cases of Norovirus infection occur in the United States each year, with over 50% of all foodborne disease outbreaks being due to Noroviruses. Most of the foodborne outbreaks are due to the handling of food by someone whose hands are contaminated with virus-laden fecal material.
A wide variety of foods can be contaminated including salad dressing, deli-style meats, bakery items, cake icing, fruits, and vegetables. Seafoods such as oysters can become contaminated and can concentrate the virus in high numbers when they filter Norovirus-laden water and then eating the raw oysters can transmit the virus to people. Drinking water can also be contaminated with Norovirus.
Norovirus infections occur anywhere in the world. Indeed, because the virus is easily spread among persons, difficult to kill, and contagious, the probability exists of repeated, large-scale outbreaks.
IN CONTEXT: PERSONAL RESPONSIBILITY AND PROTECTION
- “Many local and state health departments require that food handlers and preparers with gastroenteritis not work until 2 or 3 days after they feel better. In addition, because the virus continues to be present in the stool for as long as 2 to 3 weeks after the person feels better, strict handwashing after using the bathroom and before handling food items is important in preventing the spread of this virus. Food handlers who were recently sick can be given different duties in the restaurant so that they do not have to handle food (for example, working the cash register or hostessing).”
- “People who are sick with Norovirus illness can often vomit violently, without warning, and the vomit is infectious; therefore, any surfaces near the vomit should be promptly cleaned and disinfected with bleach solution and then rinsed. Furthermore, food items that may have become contaminated with Norovirus should be thrown out. Linens (including clothes, towels, tablecloths, napkins) soiled to any extent with vomit or stool should be promptly washed at high temperature. Oysters should be obtained from reputable sources and appropriate documentation kept. Washing raw vegetables thoroughly before eating and appropriate disposal of sewage and soiled diapers also help to reduce the spread of norovirus and prevent illness. In small home-based catering businesses or family owned or operated restaurants, sick children and infants in diapers should be excluded from food preparation areas.”
SOURCE: Centers for Disease Control and Prevention, National Center for Infectious Diseases
Treatment for a Norovirus infection consists of keeping a person hydrated and as comfortable as possible while waiting for the infection to subside.
Good personal hygiene is the best prevention strategy. Proper handwashing is crucial in preventing transfer of the virus. Similar to the viruses that cause the common cold and influenza, having an infection does not produce an immunity to future infections since there are many, slightly different version of Norovirus. An immune response to one version is not protective against other versions of the virus.
Washing fruits and vegetables before eating them, especially those labeled organically grown, is wise, as some organic produce is fertilized with manure. Because virus particles require a host cell before they can replicate, Norovirus particles that adhere to produce can remain capable of causing an infection for a long time.
The intensity of the symptoms of a Norovirus infection is of most concern when the infection occurs in settings such as a day care, cruise ship, school, or a hospital. This is because the rapid loss of fluid that occurs with repeated bouts of diarrhea and vomiting can be quickly dehydrating. In an infant or an infirmed person, the combination of the infection and dehydration can be dangerous.
The consequences of the immune catch-up response that occurs when a new version of Norovirus appears can be enormous. An example involves the high number of Norovirus infections that occurred in the United States and Europe in 2002 with the appearance of a new Norovirus variant. The majority of cases occurred in hospitals, cruise ships, and nursing homes. In some cases, patient and surgical wards and the emergency room were temporarily shut down, crippling hospital services and escalating medical costs. Cruise lines cancelled cruises, quarantined ill crewmembers, and kept ships out of service for cleaning and sanitizing. Outbreaks of Norovirus occurred in 25 cruise ships bound for U.S. ports in 2002, affecting almost 3,000 passengers. Cruise ships sailing into U.S. ports are required to notify the CDC of each case of gastroenteritis diagnosed aboard ship 24 hours prior to arrival. If the number of affected passengers or crew reaches 2%, the ship must file an alert informing U.S. health authorities of the outbreak. The CDC monitors reports of outbreaks of gastroenteritis aboard cruise ships on a daily basis, and helps to identify the causative agent.
Another outbreak of Norovirus among people in close quarters occurred in the Reliant Astrodome in Houston, Texas, during September 2005, when it was used to house evacuees from hurricane Katrina. Approximately 1,500 evacuees and relief workers received treatment for gastroenteritis at the Astrodome complex between September 2–12, 2005. The causative agent was later identified as a Norovirus, and despite the rapidly changing population of evacuees, the outbreak was contained within one week by isolating persons with symptoms within one area of the complex, distributing hand sanitizer, conducting handwashing awareness campaigns, and installing additional portable sinks in the facility.
Protection against Noroviruses in the form of a vaccine is not available, although at least one pharmaceutical company is attempting to develop an inhalable vaccine. Norovirus infection also has consequences for the military. The debilitating and contagious natures of the infection can lessen the combat readiness of troops. Recognizing this, the vaccine development effort is being largely funded by U.S. defense agencies.
IN CONTEXT: TRENDS AND STATISTICS
With regard to the disease burden of norovirus gastroenteritis, in August 2006 the Centers for Disease Control and Prevention (CDC) estimated that:
- 23 million cases of acute gastroenteritis are due to Norovirus infection, and it is now thought that at least 50% of all foodborne outbreaks of gastroenteritis can be attributed to noroviruses.
- Among the 232 outbreaks of norovirus illness reported to CDC from July 1997 to June 2000, 57% were foodborne, 16% were due to person-to-person spread, and 3% were waterborne; in 23% of outbreaks, the cause of transmission was not determined. In this study, common settings for outbreaks include restaurants and catered meals (36%), nursing homes (23%), schools (13%), and vacation settings or cruise ships (10%).
- Most foodborne outbreaks of Norovirus illness are likely to arise though direct contamination of food by a food handler immediately before its consumption. Outbreaks have frequently been associated with consumption of cold foods, including various salads, sandwiches, and bakery products. Liquid items (e.g., salad dressing or cake icing) that allow virus to mix evenly are often implicated as a cause of outbreaks. Food can also be contaminated at its source, and oysters from contaminated waters have been associated with widespread outbreaks of gastroenteritis. Other foods, including raspberries and salads, have been contaminated before widespread distribution and subsequently caused extensive outbreaks.
- Waterborne outbreaks of Norovirus disease in community settings have often been caused by sewage contamination of wells and recreational water.
SOURCE: Centers for Disease Control and Prevention, National Center for Infectious Diseases
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