Diseases & Conditions


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Norwalk agent virus infection


Infection by a family of several small viruses that can cause viral gastroenteritis with diarrhea. Although viral gastroenteritis may be caused by a number of viruses, the Norwalk family is responsible for about a third of all cases in children (except for infants). Norwalk virus is also the most common cause of viral contamination in shellfish. Although anyone can get Norwalk virus, those at highest risk are children under age four. Norwalk virus was first identified as the cause of an outbreak of gastroenteritis among children at a school in Norwalk, Ohio, and among their teachers and their families. Norwalk and Norwalk-like viruses are being recognized more frequently as important causes of food-borne disease in the United States. However, since no routine diagnostic test is available, the true prevalence is not known. Outbreaks commonly occur in schools, camps, hospitals, and, in particular during 2002 and 2003, on cruise ships. Many oyster-related outbreaks of intestinal illness linked to Norwalk-like viruses have been reported in Louisiana, Florida, Maryland, and other states where oyster harvesting is common. In 1993, 73 people in Louisiana and about 130 others in the United States who ate oysters from Louisiana became ill. A malfunctioning sewage system was the cause of an outbreak in 1996, and an outbreak in 1997 was linked to sewage from oyster-harvest-ing boats. In 2003 the U.S. Centers for Disease Control and Prevention (CDC) has assisted with four outbreaks of Norwalk virus-related gastrointestinal illness aboard cruise ships. The Sun Princess (Princess Cruise Lines) sailed from Los Angeles to Hawaii on January 25, 2003, for a 15-day cruise, but three days later, 267 of 2,029 passengers and 29 of 877 crew became sick with gastrointestinal illness. Princess Cruises terminated the cruise on February 4 as a precautionary measure and returned passengers home by airline. On a Sundream (Sun Cruises, U.K.) cruise between January 20 and February 3, 2003, gastrointestinal illness was reported in 95 of 1,085 passengers and 12 of 403 crew. The ship made one stop in St. Thomas, U.S., en route to Venezuela. The Olympia Voyager (Royal Olympic Cruises, Greece) left port from Port Everglades, Florida, and ended in Houston, and between January 15 and February 3, 2003, gastrointestinal illness was reported among 35 of 756 passengers and 5 of 356 crew. Cleaning and disinfection were initiated during the first week of the cruise and no new cases were identified on the second week. At virtually the same time, the Carnival Spirit reported 102 of 2,143 passengers and 10 of 902 crew ill on a cruise between January 27 and February 4, 2003. Stool specimens were submitted to the CDC for analysis. Extensive cleaning and disinfection were carried out on all cruise ships immediately following reports of illness, and the CDC continued to monitor the situation. Cause Outbreaks of Norwalk gastroenteritis often occur in settings where there is close contact between many children. The virus is found in stool and on hands and surfaces that have had contact with stool and can be transmitted by eating contaminated food or drinking tainted water. In addition, the virus can be transmitted from person to person. Water is the most common source of outbreaks and may include water from city supplies, wells, recreational lakes, swimming pools, and water stores in cruise ships. Shellfish and salad ingredients are foods most often implicated in Norwalk outbreaks. The virus is destroyed by cooking but not by freezing Everyone who ingests the virus and who has not recently had an infection with the same strain is susceptible to infection and can develop symptoms. Infection is most common in older children (and adults). Symptoms Within two to three days of infection, symptoms of vomiting, abdominal cramps, mild diarrhea, fatigue, and muscle aches appear. Most people experience only a mild illness and recover within 48 hours. About three months after infection, children will develop a short-term immunity. After this period of time, however, it is possible to be reinfected. Severe illness or hospitalization is very rare. Diagnosis Research labs can look for virus in stool specimens; a blood test can uncover antibodies to the virus. Specific diagnosis of the disease can only be made by a few labs. Treatment Because the diarrhea is caused by a virus, there is no cure. When a person becomes infected, the body develops antibodies that destroy the virus. Rest, clear fluids, and acetaminophen for headaches and body aches will help. Patients who do not experience vomiting can continue to eat solids. Prevention There are no specific preventive measures, since scientists do not know enough about how the virus is transmitted. However, it is wise to follow guidelines for avoiding food-borne illness and follow precautions for food and beverage safety when traveling to tropical countries. Hands should be washed before preparing or serving foods, and someone else should prepare food if the cook has cramps, nausea, vomiting, diarrhea, or open sores on the hands. Children and their caregivers should wash thoroughly before eating and after toileting.