Background Human norovirus (HuNoV) is the major cause of viral acute gastroenteritis for all age groups in various countries. HuNoV GII in particular accounted for the majority of norovirus outbreaks, among which GII.4 caused repeated outbreaks for a long time. Besides GII.4, other norovirus genotypes, GII.2, GII.6, and GII.17, have also been prevalent in various contexts in recent years, but few detailed epidemiological studies of them have been performed and are poorly understood. We thus conducted an epidemiological analysis of HuNoV GII in Ibaraki Prefecture, Japan, by performing surveillance in the six seasons from September 2012 to August 2018. Results HuNoV GI occurred almost sporadically for all genotypes; however, each genotype of GII exhibited its typical epidemiological characteristics. Although the number of outbreaks of GII.4 decreased season by season, it reemerged in 2017/2018 season. The timing of the epidemic peak in terms of number of cases for GII.17 differed from that for the other genotypes. The patients age with GII.2 and GII.6 were younger and outbreak of GII.17 occurred frequently as food poisoning. Namely, the primarily infected outbreak group differed for each genotype of HuNoV GII. Moreover, the viral load of patients differed according to the genotype. Conclusions Various HuNoV genotypes including GII.2, GII.4, GII.6, and GII.17 were shown to be associated with various types of outbreak sites (at childcare and educational facilities, involving cases of food poisoning, and at elderly nursing homes) in this study. These genotypes emerged in recent years, and their prevalence patterns differed from each other. Moreover, differences in outbreak sites and viral load of patients among the genotypes were identified.

中文翻译：

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2012-2018 年在日本茨城县检测到的人类诺如病毒 GII 基因型变异。

背景 人类诺如病毒 (HuNoV) 是各国所有年龄组病毒性急性胃肠炎的主要原因。尤其是 HuNoV GII 占诺如病毒暴发的大部分，其中 GII.4 引起了长时间的反复暴发。除 GII.4 外，其他诺如病毒基因型 GII.2、GII.6 和 GII.17 近年来在各种情况下也很普遍，但对它们的详细流行病学研究很少，而且了解甚少。因此，我们通过在 2012 年 9 月至 2018 年 8 月的六个季节进行监测，对日本茨城县的 HuNoV GII 进行了流行病学分析。结果所有基因型的 HuNoV GI 几乎都是零星发生的；然而，每个 GII 基因型都表现出其典型的流行病学特征。虽然 GII 爆发的次数。4 逐季减少，2017/2018 赛季再度出现。GII.17 病例数的流行高峰时间与其他基因型不同。GII.2和GII.6患者年龄较小，GII.17暴发多见于食物中毒。即，HuNoV GII 的每种基因型的主要感染暴发组都不同。此外，患者的病毒载量因基因型而异。结） 在这个研究中。这些基因型是近年来出现的，它们的流行模式彼此不同。而且，