Occurrence of Norovirus in an Asymptomatic Food-handler population unrelated to Norovirus Outbreaks

Department of Microbiology, Sapporo Medical University School of Medicine, S1-W17, Chuou-ku, Sapporo, Hokkaido, 060-8556, Japan; Hokkaido Laboratory, SRL Co., Ltd., S19-W13, Chuou-ku, Sapporo, Hokkaido, 064-0919, Japan; Sapporo City Institute of Public Health, Kikusui 9-1, Shiroishi-ku, Sapporo, Hokkaido, 003-8505, Japan

^* To whom correspondence should be addressed. Email: tamaoka{at}sapmed.ac.jp.

	Abstract

Norovirus (NV) is the most common causative agent of nonbacterial gastroenteritis. Surveillance of NV in facilities that reported outbreaks are frequently found in publications, but that in facilities without outbreaks are not found. We investigated the molecular epidemiology of NV derived from asymptomatic food handlers working at a non-outbreak food catering facility in Hokkaido, Japan from February to March in 2005 and January to February in 2006 by RNA polymerase gene sequencing. Approximately 12% (20/159) of the samples were positive for genogroup II (GII, 10.1% in 2005 and 14.2% in 2006). The GI genotypes were not detected. The data from the phylogenetic analysis indicated that, among the 20 strains detected, 13 strains were genogroup II/genotype 2 (GII/2), 2 were GII/3, 3 were GII/8, and 2 were GII/12. GII/4, which has been found most frequently in recent outbreaks worldwide, including Japan, was not detected. We found that one individual was co-infected with two genotypes, GII/2 and GII/12. This is the first report of the detection of NV genotypes in asymptomatic food handlers working at a non-outbreak facility. The excretion of NV from healthy individuals may be an infection source of NV outbreaks as well as other food-borne diseases.