What is the Norwalk virus? Several co-workers were diagnosed with this infection after eating cheese products at a local restaurant.

K.G.

Several viruses cause gastrointestinal illness in adults and children. Among the most common are the Norwalk virus and its relatives, called Norwalk-like viruses. Infections with these viruses are extremely common in sporadic cases as well as larger outbreaks. One such outbreak involved an elementary school in Norwalk, Ohio -- which is how the virus got its name.

The incubation period (the time between infection and disease) is about one to two days. Symptoms may develop abruptly. Usually there will be some combination of nausea, vomiting and diarrhea. There can also be muscle aches, general ill feeling and low-grade fever. The symptoms disappear in a few days, almost always with complete recovery.

It is very difficult to specifically diagnose Norwalk infection as opposed to a variety of other illnesses. Since the disease goes away without treatment, it is not very important to establish the diagnosis in most instances. In addition, there are no specific treatments. On occasion, a patient becomes severely dehydrated and requires intravenous fluids.

When people are infected with one of the Norwalk group of viruses, they become immune to re-infection. However, the immunity is directed only against the particular virus causing the infection, and the immunity is rather short-lived. After six months to two years, the same virus can cause infection again.