Background: Although many studies on asymptomatic norovirus infection in outbreaks have been conducted globally, structured data (important for emergency management of outbreaks) on the prevalence of this epidemic are still not available. This study assessed the global prevalence of asymptomatic norovirus infection in outbreaks. Methods: We identified publications on asymptomatic infections from norovirus outbreaks by searching the PubMed, Embase, Cochrane Library, Medline, and Web of Science databases and screening references from the articles reviewed. Prevalence of asymptomatic norovirus infection in outbreaks was employed as the primary summary data. The random-effects model of the meta-analysis was fitted to generate estimates of the prevalence in the overall and subgroup populations. Results: In total, 44 articles with a sample size of 8,115 asymptomatic individuals were included. The estimated pooled prevalence of asymptomatic norovirus infection in outbreaks was 21.8% (95%CI, 17.4–27.3). The asymptomatic prevalence of norovirus GII (20.1%) was similar to that of GI (19.8%); however, the proportion prevalence of asymptomatic individuals involved in the former (33.36%) was significantly higher than that of in the latter (0.92%) and the former (93.18%) was reported much more frequently than the latter (15.91%) in the included articles. These studies had significant heterogeneity (I² = 92%, τ² = 0.4021, P < 0.01). However, the source of heterogeneity could not be identified even after subgroup analysis of 10 possible influencing factors (geographical area, outbreak settings, outbreak seasons, sample types, norovirus genotypes, transmission routes, subjects’ occupations, subjects’ age, per capita national income, and clear case definition). Meta-regression analysis of these 10 factors demonstrated that the geographical area could be partly responsible for this heterogeneity (P = 0.012). Conclusions: The overall pooled asymptomatic prevalence of norovirus in outbreaks was high, with genome II dominating. Asymptomatic individuals may play an important role in norovirus outbreaks. This knowledge could help in developing control strategies and public health policies for norovirus outbreaks.

BACKGROUND Norovirus outbreaks frequently occur in semi-closed environments like schools and kindergartens. Current strategies are inadequate. This study aimed to examine several important characteristics of norovirus outbreaks in kindergartens, primary schools, and junior high schools reported to the Xi'an Center for Disease Control and Prevention (CDC) between October 2020 and February 2023. MATERIAL AND METHODS Data were obtained from the Xi'an CDC. Attack rates, vomiting rates, diarrhea rates, norovirus detection rates, and asymptomatic prevalence among exposed populations were analyzed using a random-effects meta-analysis model. Between-group comparisons were made using the Wilcoxon signed-rank test and Kruskal-Wallis H test. RESULTS Forty-four norovirus outbreaks were analyzed, involving 33 kindergartens and 11 schools, with 7945 exposed individuals and 768 cases. The overall attack rate was 29.1% (95% confidence interval [CI]: 22.9-35.6). Vomiting was reported in 90.9% of the cases (95% CI: 84.6-95.9), whereas diarrhea occurred in 23.3% of the cases (95% CI: 15.8-31.5). Norovirus was detected in 65.6% of the cases (95% CI: 57.6-73.2) using PCR-based methods. Additionally, the asymptomatic prevalence during the outbreaks was 17.4% (95% CI: 9.7-26.3). CONCLUSIONS These findings reveal the impact of norovirus on student populations in schools and kindergartens. Understanding the epidemiological characteristics of norovirus outbreaks enables the prompt identification of norovirus as a potential causative agent in an acute gastroenteritis outbreak. This facilitates the timely implementation of control measures, limits the spread and scale of these outbreaks, shortens their duration, guides the efficient allocation of medical resources, and reduces unnecessary resource consumption.

Sapovirus is gaining recognition as a significant non‐bacterial causative agent of acute gastroenteritis globally, contributing to both sporadic cases and outbreaks across all age groups. In China, it is identified as the second most prevalent pathogen responsible for acute gastroenteritis outbreaks, following norovirus, which underscores its public health importance. Consequently, an extensive systematic review and meta‐analysis are undertaken to evaluate the prevalence and genotype distribution of sapovirus among patients presenting with acute gastroenteritis. This analysis incorporated 159 eligible studies spanning 32 provinces in China. The estimated overall prevalence of sapovirus is 1.9% (95% CI: 1.7–2.2), with an asymptomatic prevalence of 0.8% (95% CI: 0–2.5). Notably, in outbreak settings, the respective prevalence rates increase substantially to 16.4% (95% CI: 10.1–23.8) and 14.4% (95% CI: 8.9–20.7). Furthermore, these findings reveal that sapovirus GI genomes predominated in both sporadic and outbreak contexts, with genotypes GI.1, GI.2, and GII.1 being most frequently identified. These insights are crucial for enabling governments to accurately assess disease burden, inform the development of targeted vaccines, and establish evidence‐based public health policies and emergency response strategies to mitigate sapovirus outbreaks.