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Detection of Norovirus in Swab Specimens of Restrooms and Kitchens Collected for Investigation of Suspected Food Poisoning Outbreaks in Tokyo.

During 2015-2016, we examined norovirus (NoV) RNA in swab specimens collected for investigation of suspected food poisoning outbreaks in Tokyo by real-time RT-PCR. Of 1,726 swab samples, 65 (3.8%) were NoV-positive and all positive swab samples were derived from NoV-positive outbreaks. Swab specimens were positive in 41 of 181 (22.7%) NoV outbreaks, while no positive swabs were detected in NoV-negative outbreaks. PCR fragments amplified from 32 swabs were sequenced, and all of them displayed complete homology with sequences from clinical and food samples. Though the results of swabs may be useful for determining the causative agent and infection route in some outbreaks, there was no case in which the results of swabs alone could elucidate the cause of food poisoning. Swabs may be useful in food poisoning investigations, if the results are interpreted in conjunction with epidemiological findings and clinical data. Swab samples are often collected several days after an outbreak, and the influence of disinfection should be taken into consideration. In NoV outbreaks, 55 out of 640 (8.6%) restroom swab specimens were NoV-positive whereas six of 618 (1.0%) were positive among kitchen swab specimens. In the restroom, the toilet bowl (43.6%) showed the highest positive rate and next was the toilet seat (14.5%). Additionally, NoV was detected at various sites in the restroom, including doorknob and floor. Since NoV-positive swab specimens may suggest that sanitation management is not performed properly in the facility, swab results may be utilized as a basis for hygiene guidance.