tbc said:

What would be the best way to try and detect the presence of the Norwalk Virus in food. For example, if an outbreak is suspected to come from a certain salad bar can the components of the salad bar be assayed? Thanks, in advance, for any replies.

Epidemiological investigations of outbreaks associated with theses viruses have been hindered by the lack of available methods for the detection of NLVs and HAV in foodstuffs. Although reverse transcription ( RT)-PCR methods have been useful in detecting NLV( Norwalk Like Virus) and HAV Hepatitis A virus) in bivalve mollusks.
There is a method developed for other foods to recover viral RNA:
wash food samples with a guanidinium-phenol-based reagent, extraction with chloroform, and precipitation in isopropanol. Recovered viral RNA is amplified with NLV-specific primers in RT-PCRs, using a viral RNA standard control to identify potential sample inhibition. These are methods used for beef and turkey. Could you use it for salad bars? it seems pretty complex.
I hope I helped.