Outbreak of Norwalk-like virus infection associated with salad provided in a restaurant.

Preliminary enquiries following the reporting of some cases of suspected food poisoning by members of the public revealed that they had all eaten at the same restaurant during the preceding weekend. Subsequent investigation, including a merged cohort study, identified 49 people with gastrointestinal symptoms, six of whom showed evidence of infection with Norwalk-like virus (NLV). Over a four day period all had eaten at the restaurant. Eating salad was strongly associated with infection. One of the chefs, who handled salad in the food preparation area and who had been absent from work with symptoms of gastrointestinal illness, had returned to work the day before the four-day period, reporting that he was 48-hours symptom free. He was subsequently shown to have been infected with NLV by reverse transcriptase polymerase chain reaction (RT-PCR) assay. The NLV belonged to the same genogroup as that infecting the cases who had eaten at the restaurant.