not-yet-known not-yet-known not-yet-known unknown Systematic Review of Norovirus Outbreaks in China: Epidemiological Characteristics and Transmission Variations.

Norovirus represents one of the primary pathogens responsible for gastroenteritis on a global scale, exerting a significant impact on foodborne illnesses. In recent years, China has emerged as a region of particular significance with regard to the occurrence of norovirus outbreaks. This study presents a systematic review of norovirus outbreaks in China, offering a comprehensive overview and analysis of norovirus epidemics. A total of 680 articles reporting 798 outbreaks were included from four databases (CNKI, CHINA Wanfang, Web of Science, and PubMed). Firstly, an overall historical review of norovirus outbreaks in China over the past two decades is conducted, detailing the fluctuations in reported outbreak numbers and cases influenced by different global strains and the COVID-19 pandemic. A comparison of the changes in the scale of outbreaks (the number of cases, attack rate, duration, and reporting time), significant differences are found in the number of cases and duration of outbreaks (P<0.001). Furthermore, the epidemiological characteristics are examined from five perspectives: region, seasonality, setting, transmission, and genogroup. It was found that high-incidence regions are concentrated in the southern and eastern regions of China, with outbreaks primarily occurring in winter. Schools are identified as key outbreak setting, and foodborne transmission is the main mode of transmission. The GII genogroup is particularly prevalent, with GII.2 and GII.4 being the most dominant. Based on above findings, the article also cross-analyzes seasonal variations in different provinces and transmission modes under different settings and genogroups. In most settings, foodborne transmission is the primary mode, whereas person-to-person and waterborne transmission prevail in settings like schools and communities, respectively. The GII genogroup primarily spread through person-to-person contact, food, and aerosols caused by vomiting. In contrast, the GI genogroup and I/II mixed genogroups mainly spread through water and food.