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A study conducted by the Centers for Disease Control and Prevention and published in Emerging Infectious Diseases has found that most norovirus outbreaks are caused by food workers handling food. Norovirus is the leading cause of foodborne illness outbreaks in the United States, responsible for 58% of all outbreaks from known agents.

The virus is spread through several methods: person-to-person transmission, ingestion of aerosolized vomitus, and indirect transmission through contaminated surfaces, food, or water. The virus can stay alive on surfaces for two weeks and in water for more than two months. It is also quite resistant to many disinfectants. The most frequent pathways to contamination are through infected food workers or exposure to water contaminated with fecal material.

According to the study, leafy vegetables, fruits, nuts, and mollusks are the most common food sources resulting in norovirus outbreaks. The likely point of transmission was in food preparation or service.

During the period of 2001 to 2008, 9,206 food poisoning outbreaks were reported in the U.S. Only 6,355 had a known cause. Of those, 46% or 2,922 of the outbreaks were caused by norovirus. The outbreaks were reported from 49 states (Vermont being the only exception) and Washington D.C. the highest per capital rates were in Minnesota and Oregon; the lowest in Texas and Kentucky. The greatest number of outbreaks were in California. Outbreaks are more frequent in winter months, but the seasonal pattern varied from year to year. The outbreaks were most often caused by food prepared in commercial settings.

Since an average of one outbreak is reported every day, food handler contact with raw and ready-to-eat foods is the most common scenario resulting in an outbreak. Interventions need to be conducted in restaurants, delis, and other commercial settings. Using gloves to prepare food, stressing appropriate hand washing, preventing ill staff from working, and the presence of a certified kitchen manager are recommended as ways to reduce these outbreaks. The report ends by stating that more development of methods for detecting norovirus in foods are critically needed, and public health officials must define the duration of infectiousness of ill food handlers.