Norwalk is an extremely common family of viruses that cause non life-threatening forms of gastroenteritis or food poisoning. It's so common, in fact, that only the common cold is reported more frequently as a cause of illness.

Once called winter vomiting disease, the virus is named after an outbreak in Norwalk, Ohio, when the pathogen was first identified 30 years ago. Later, other viruses with similar features were described and are called Norwalk-like viruses. The virus itself is called a calicivirus because of the virus's characteristic "Star of David" shape with cup-shaped indentations.

Symptoms of Norwalk infection are not pleasant: severe nausea, severe vomiting, and severe diarrhea. Thankfully, the symptoms usually last just one to three days, with no permanent effects. Hospitalization is rarely required, though may be necessary if dehydration occurs.

Laboratory diagnosis of Norwalk is difficult, so diagnosis is often based on the observation of a combination of symptoms and the short duration of the illness.

Once infected, a Norwalk sufferer will develop immunity for a time, but the immunity is not permanent and reinfection can occur. That's because of the large number of Norwalk-like viruses. A bout with one won't necessarily make you immune to another.

Norwalk-like viruses are spread through food and water contaminated with infected feces. Those infected can then pass it on through physical contact with others.

The virus is commonly transmitted from person to person in cold weather, when people are indoors more often and in closer contact. It flourishes in environments such as cruise ships and nursing homes, where hundreds of passengers and crew mingle in close quarters, providing ideal conditions for a virus to spread.

Water is the most common source of outbreaks and may include water from municipal supplies, well, recreational lakes, swimming pools, and water stored aboard cruise ships. The virus is also particularly resilient out of the water too, with teh ability to survive for days on objects such as bathroom facuets and doorknobs.

Shellfish and salad ingredients are the foods most often implicated in Norwalk outbreaks. Ingestion of raw or insufficiently steamed clams and oysters poses a high risk for infection with Norwalk virus. Foods other than shellfish are contaminated by ill food handlers.

To prevent Norwalk virus infection, wash hands often with soap and warm water, particularly after every toilet visit and before preparing or eating food. Cook all shellfish thoroughly before eating and wash raw vegetables before eating.

If you get the virus, there is little really treatment that will help. If you can keep it down, anti-nauseants such as Gravol can help. The diarrhea will require you to drink plenty of fluids. It will also mean you'll need to be near a bathroom, so forget about going to work. Besides, no one there wants you bringing the bug there either.