Causes of Norwalk-like viruses


Cause of Norwalk-like viruses: Viral gastroenteritis due to caliciviruses has been associated with eating contaminated oysters. Oysters can become contaminated before harvest or during preparation. Water and ice are other sources of infection. 1

Cause details for Norwalk-like viruses: Later in food processing, other foodborne microbes can be introduced from infected humans who handle the food, or by cross contamination from some other raw agricultural product.  For example, Shigella bacteria, hepatitis A virus and Norwalk virus can be introduced by the unwashed hands of food handlers who are themselves infected.  In the kitchen, microbes can be transferred from one food to another food by using the same knife, cutting board or other utensil to prepare both without washing the surface or utensil in between.  A food that is fully cooked can become recontaminated if it touches other raw foods or drippings from raw foods that contain pathogens.  2

Shellfish become contaminated via infected fecal matter from sick food handlers, or by the practice of some harvesters and/or recreational boaters of dumping raw sewage overboard. (Note: the only source of calicivirus is feces from sick persons.) 1

Since 1993, three oyster-related gastroenteritis outbreaks, attributed to calicivirus, have been documented in Louisiana. In 1993, 73 persons 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. The current outbreak implicates sewage from oyster harvesting vessels as the probable source. 1

Oyster-related outbreaks probably will continue to occur until seafood regulators and the oyster industry develop and enforce standards for proper disposal of human sewage. Food handlers with symptoms of Norwalk-like illness should limit contact with other persons and be excluded from food handling and preparation. 1

Related information for causes of Norwalk-like viruses: Further relevant information on causes of Norwalk-like viruses may be found in the risk factors for Norwalk-like viruses and underlying causes of Norwalk-like viruses.

1. excerpt from Facts About Norwalk-like Viruses: CDC-OC
2. excerpt from Foodborne Infections General: DBMD

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