Norovirus is responsible for 20% of acute gastroenteritis worldwide. The fecal-oral route of transmission is known, but we proposed a first attempt to identify the relative importance of different sources and vehicles for sporadic cases using meta-analysis models. Case-control and cohort/cross-sectional studies were systematically reviewed and analyzed to assess the main risk factors associated with sporadic norovirus infections. Suitable scientific articles were identified through systematic literature search and subjected to a methodological quality assessment. Mixed-effects meta-analyses models were adjusted by population type to appropriate risk factor categories. The quality assessment stage led to include 14 primary studies conducted between 1993 and 2014. From these, eight studies investigated exposures in children/infants, and eight concerned the mixed population.

The meta-analysis confirmed the oro-fecal route for norovirus infections, with the person-to-person transmission (pooled OR=3.002; 95% CI: [2.502-3.062] in mixed population), and the lack of personal hygiene (pooled OR=2.329; 95% CI: [1.049-5.169]). The meta-analysis also enlightened the role of indirect transmission through the environment with pathways like untreated drinking water (mixed population), with a pooled OR=2.680 (95% CI: [1.081-6.643]) and farm environment (children population). Indirect transmission also involved the food pathway, which was finally found significant with consumption of seafood (mixed population) (pooled OR=2.270; 95% CI: [1.299-3.968]) and composite food (eating outside/uncooked mixed and young population) (pooled OR=4.541; 95% CI: [3.461-5.958]).

These results are coherent with the findings from studies on outbreaks. However, a too broad definition of exposure factors limited the interpretation of results, as occurred with the seafood pathways that combined fish and shellfish. Other factors such as consumption of Food-handled products or the type of drinking water deserveE to be better investigated. Furthermore, better harmonization in case definition and appropriate case-control or cross-sectional studies would allow better addressing sporadic cases risk factors, especially for susceptible populations, such as children, elderly or immunosuppressed persons.

诺如病毒占全球急性胃肠炎的20％。粪便的传播途径是已知的，但我们提出了首次尝试，使用荟萃分析模型确定散发病例的不同来源和媒介的相对重要性。系统地审查和分析了病例对照研究和队列研究/横断面研究，以评估与散发性诺如病毒感染相关的主要危险因素。通过系统的文献检索确定合适的科学文章，并进行方法学质量评估。根据人群类型将混合效应荟萃分析模型调整为适当的危险因素类别。质量评估阶段包括1993年至2014年进行的14项主要研究。其中有8项研究调查了儿童/婴儿的暴露情况，

荟萃分析证实了诺如病毒感染的经口粪便途径，人与人之间的传播（混合OR = 3.002；混合人群中95％CI：[2.502-3.062]）和缺乏个人卫生（合并） OR = 2.329； 95％CI：[1.049-5.169]）。荟萃分析还启发了通过未经处理的饮用水（混合人口），OR = 2.680（95％CI：[1.081-6.643]）和农场环境（儿童人口）等途径通过环境间接传播的作用。间接传播也涉及食物途径，最终发现与食用海鲜（混合人群）（合并OR = 2.270； 95％CI：[1.299-3.968]）和复合食品（在外面/未煮过的混合和年轻人群中进食）有关。 （合并OR = 4.541； 95％CI：[3.461-5.958]）。

这些结果与关于暴发的研究结果相一致。但是，暴露因子的定义太宽泛，限制了结果的解释，就像结合鱼类和贝类的海鲜途径所发生的那样。其他因素，例如食品处理产品的消费或饮用水的类型，值得进一步研究。此外，更好地协调病例定义和进行适当的病例对照或横断面研究，将能够更好地解决散发病例的危险因素，特别是对于易感人群，如儿童，老人或免疫抑制的人群。