Norwalk Viruses Widespread

All of us know someone who has been ill with a “stomach bug” this season. Many of these are undefined viral or bacterial illnesses that typically cause some discomfort for a few days and then disappear as mysteriously as they showed up. But there’s a good chance that the culprit may have been either the Norwalk virus or one of its many relatives.

Norwalk virus caused an outbreak of illnesses in Norwalk, Ohio in the 1970’s, and each subsequent related outbreak has been termed “Norwalk-like.” The viruses are second only to the common cold in the occurrence of viral illnesses in the US. The Centers for Disease Control and Prevention (CDC) reports that an estimated 181,000 cases of Norwalk or Norwalk-like infection occur annually in the United States. The high incidence was brought to light last year when hundreds of cruise ship passengers became ill during their trips. The outbreaks, which took place on ships from several different companies, were all determined to be associated with Norwalk-like viruses.

Mary Beth Graham, MD, Assistant Professor of Infectious Diseases at the Medical College of Wisconsin, says that symptoms of Norwalk virus infection include nausea, vomiting, diarrhea and abdominal cramps. Headache and low-grade fever may also occur. “Fortunately,” reports Dr. Graham, “this is a self-limited illness, and people usually recover in 24 to 72 hours. The Norwalk and Norwalk-like family of viruses are representative of a larger group of viruses called the caliciviruses. Infection with these viruses affects the intestine and is a common cause of gastrointestinal illness. Dr. Graham reports that as many as one-third of all of reported gastroenteritis cases could be associated with Norwalk viruses. “Accurate documentation is difficult because Norwalk is virtually indistinguishable from any other gastroenteritis,” reports Dr. Graham, and testing is usually not cost-effective.

Where Do the Viruses Come From?
“Humans are the only hosts of these viruses,” said Dr. Graham. “The illness is carried in human fecal material.” Fecal-oral contamination can occur when people involved in food preparation don’t properly wash their hands or the food prep area. Shellfish such as oysters and clams often become contaminated via infected fecal matter from sick food handlers, or by the practice of some harvesters and recreational boaters of dumping raw sewage overboard. Other foods associated with outbreaks have been linked to cold-prepared, ready-to-eat foods such as salads, coleslaw and sandwiches. Outbreaks have also been connected to drinking water and recreational water from pools, ponds or lakes where swimmers could have ingested water contaminated with feces from an infected person.

How Do the Viruses Spread?
Norwalk and Norwalk-like viruses are transmitted when people consume food or water contaminated with feces from an infected person. These viruses are easily spread from person-to-person. Dr. Graham reminds us that it’s not possible to become immune to a Norwalk-like virus. “Just because you’ve had it once doesn’t mean you’ll never get it again.”

What Are the Symptoms of Infection?
The most common symptoms of infection with the Norwalk viruses are nausea with vomiting, diarrhea, and cramps. These symptoms occur in all age groups, although diarrhea is more common among adults and vomiting is more common in children. Many people also experience headache, fever, chills and muscle aches. The symptoms usually appear within 24 to 48 hours after exposure to the virus, but might appear any time from 10 to 50 hours after exposure. People are infectious (and able to spread the disease) as long as symptoms are present, and up to four days after diarrhea has stopped.

How Do I Avoid Infection?
Thorough handwashing following toilet use and prior to handling food is the best way to prevent the spread of these viruses. “Washing hands is the most obvious way to avoid transmitting the virus,” says Dr. Graham. “And the new alcohol-based hand rubs are very effective when soap and water are not available.” Dr. Graham emphasizes that people who are already ill should never prepare food for anyone else. In addition, those currently ill with diarrhea or vomiting should not work in day care centers or care for patients in a health care facility until these symptoms have stopped.

No Specific Treatment
Illnesses caused by Norwalk viruses have no specific treatment. Rest and oral rehydration are recommended, and Dr. Graham suggests drinks such as Pedialyte, Gatorade or juices, rather than plain water, because they have added salts and nutrients that your body needs. “Try to avoid milk,” says Dr. Graham, “because it might not be digested as well as the oral rehydration solutions and can cause additional gastrointestinal problems.” Dr. Graham also suggested the following recipe for an oral rehydration drink that approximates most store-bought solutions can be prepared inexpensively at home:

To one liter of water, add