Hepatitis E virus (HEV) is one of the main causes of viral hepatitis infection worldwide. Sources of contamination can vary greatly according to geographical regions and HEV genotypes. HEV is endemic and responsible for large waterborne epidemics involving human HEV-1 or HEV-2 genotypes in regions with limited sanitation, in contrast to industrialized countries, where HEV is mainly a foodborne zoonosis involving HEV-3 and HEV-4 zoonotic genotypes. Limited data on HEV source attribution are available, and all possible sources and transmission pathways of HEV are not fully identified.

A systematic review and a meta-analysis of case-control and cohort studies (including transversal studies) were performed to determine the main risk factors associated with sporadic hepatitis E infection. Suitable scientific articles were identified through a systematic literature search and subjected to a methodological quality assessment. From each study, odds-ratio (OR) measures were extracted/calculated, as well as study characteristics such as population type, design, and risk factor hierarchy. Mixed-effects meta-analyses models were adjusted by population type to appropriate data partitions.

Seventy-seven cohort and case-control studies conducted between 1986 and 2016 and investigating risk factors in mixed population, susceptible population, and pregnant women, were included in this meta-analysis. Hepatitis E cases were defined with serological exams and differentiated whenever the serological exam is associated or not with symptoms.

This meta-analysis identified the parenteral pathway (blood transfusion, tattooing or IV injection, dialysis or hemodialysis), and routes of infection related to contaminated water, animal contact (occupational exposure) and consumption of foods as relevant risk factors for hepatitis E infection.

With regards to the role of food, as suspected and sometimes proven in several studies, pig meat, pork sausages, and game meat are identified as significant risk factors for HEV, in particular undercooked pig meat, or meat preparations containing pig liver. In addition, consumption of shellfish (oysters and mussels), in which HEV can accumulate when water is environmentally contaminated (from animal or human origin), is also associated with the detection of anti-HEV antibodies.

The results of this meta-analysis show that symptomatic and infected cases share the most explainable risk factors, and are in agreement with recent studies conducted in Europe. This meta-analysis reveals that some sources such as consumption of insufficiently treated water, shellfish, or vegetables are under-investigated. Future case-control studies should include population at risk but under-investigated, such as transplant recipients, pregnant women and children, and investigate other potential sources of HEV.

戊型肝炎病毒（HEV）是全世界病毒性肝炎感染的主要原因之一。污染的来源根据地理区域和HEV基因型的不同而有很大差异。HEV是地方性的，并负责在卫生条件有限的地区中涉及人类HEV-1或HEV-2基因型的大型水传播流行病，而工业化国家则主要是食源性人畜共患病，涉及HEV-3和HEV-4人畜共患病基因型，与此相反。有关HEV来源归因的数据有限，并且尚未完全确定所有可能的HEV来源和传播途径。

进行了病例对照研究和队列研究（包括横向研究）的系统评价和荟萃分析，以确定与散发性戊型肝炎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。从每项研究中，提取/计算比值比（OR）以及研究特征，例如人口类型，设计和危险因素等级。根据人群类型将混合效应荟萃分析模型调整为适当的数据分区。

这项荟萃分析包括1986年至2016年之间进行的77项队列研究和病例对照研究，研究了混合人群，易感人群和孕妇的危险因素。戊型肝炎病例通过血清学检查确定，并在血清学检查与症状无关或没有症状时进行区分。

这项荟萃分析确定了肠胃外途径（输血，纹身或静脉注射，透析或血液透析）以及与污水，动物接触（职业接触）和食用食物有关的感染途径是戊型肝炎感染的相关危险因素。

关于食品的作用，如若干研究中怀疑和有时证实的那样，猪肉，猪肉香肠和野味被确定为戊型肝炎病毒的重要危险因素，特别是未煮熟的猪肉或含有猪肝的肉制品。此外，食用贝类（牡蛎和贻贝）时，HEV会在环境受到水污染时（动物或人源）在其中积聚HEV，这也与抗HEV抗体的检测有关。

荟萃分析的结果表明，有症状和感染的病例具有最可解释的风险因素，并且与欧洲最近进行的研究一致。这项荟萃分析显示，某些来源，例如未充分处理的水，贝类或蔬菜的消费量，尚未得到充分研究。未来的病例对照研究应包括处于危险之中但研究不足的人群，例如移植受者，孕妇和儿童，并调查其他可能的戊型肝炎病毒来源。