学校給食で提供された刻みのりによるノロウイルス食中毒

摘要

In February 2017, four food poisoning outbreaks occurred in Tokyo, involving ten schools. Shredded dried laver seaweed processed by a single food manufacturer in December 2016 was provided in common for the school meals that caused all four outbreaks. Of 4,209 persons exposed, 1,193 (28.3%) had symptoms of gastroenteritis. Norovirus (NoV) GII was detected in 207 (78.1%) of 265 cases by real-time RT-PCR. Thirty-one shredded dried laver seaweed samples were examined and seven (22.6%) of them were positive for NoV GIL PCR fragments of NoV ORF1/2 junction region (302 bp) from seven shredded dried laver seaweed samples and 20 clinical samples derived from the four outbreaks were sequenced. All of them displayed complete homology, and the genotype was classified as GII.17. A nearly full-length sequence (7,420 bp) of NoV RNA derived from a case was obtained by next-generation sequencer analysis and phylogenetic analysis indicated that this strain belongs to the same cluster as Hu/GII/JP/2015/GII.P17_GII.17/Kawasaki308. Thus, our investigation elucidated that the causative agent of these four serial food poisoning outbreaks was NoV GII.17 and the infectious source was a single batch of shredded dried laver seaweed. The water activity of the shredded dried laver seaweed was found to be 0.119 to 0.129. It was epidemiological-ly clarified that NoV does not lose infectivity for about two months even in the dry state. We conclude that a large diffuse outbreak of food poisoning caused by NoV GII.17 contamination of shredded dried laver seaweed had occurred in Tokyo. Our elucidation of the causative agent indicated that the food poisoning outbreaks in multiple areas of Japan, including Tokyo, during January to February 2017 were caused by the same contaminated food.%2017年2月.東京都内で食中毒が4事例発生した.患者は10の学校 にわたり，このうち7校および1校では，それぞれ別の共同調理場で調理 された給食を提供されており，2校では自校で調理した給食を喫食してい た.全事例に共通して提供されていたものは，同一業者が2016年12月に 製造した刻みのりであった.喫食者4,209名のうち.1,193名(28.3%)が 胃腸炎症状を呈し，リアルタイムRT-PCRによる検査の結果，4事例の 患者265名中207名（78.1%)からノロウィルス（NoV) GIIが検出され た.刻みのり31検体が検査に供されたが，このうち7検体（22.6%)が NoVGII陽性となった.刻みのり7検体と4事例に由来する患者20検体の NoV ORF1/2ジャンクション領域302塩基の配列は一致し，その遺伝子型 はGII.17であった.また次世代シークェンサーによる解析により，患者 検体からほぼ全長（7,420塩基）のNoV塩基配列が得られたが，同株は系 統樹解析でHu/GII/JP/2015/GII.P17_GII.17/Kawasaki308株と同じクラス ターに属した.これらの結果から，今回の4事例は同一刻みのりを感染源と したNoVGII.17によるものであると断定された.刻みのり検体の水分活性 は0.119~0.129であり，NoVは乾燥状態でも2か月間は感染性を失わない ことが疫学的に示された.本事例の解決を発端として，刻みのりが関連した NoVGII.17による大規模なdiffuse outbreakの国内発生が明らかとなった.