Evaluating the effect of class closure strategies on norovirus outbreaks in educational settings

Class closure is the most commonly used strategy for controlling norovirus outbreaks in China. This study aimed to evaluate the efficacy of class closures in preventing and managing norovirus outbreaks in educational settings and to identify the most effective timing for implementing such interventions. From October 2020 to February 2023, data on norovirus outbreaks in schools and kindergartens managed by the Xi’an Center for Disease Control and Prevention (CDC) were collected and analyzed. Outbreaks in which classes were suspended before local CDC intervention were categorized as the class closure group. Outbreaks without class closures before CDC intervention were selected as the non-class closure group at a 1:1 ratio based on institutional type, location, and number of cases at the time of local CDC intervention. Differences between the two groups in terms of new cases, number of new affected classes, outbreak duration (in days) from CDC intervention to resolution, the terminal attack rate, and other relevant metrics were analyzed using the paired Wilcoxon signed-rank test. Multivariable linear regression analysis was performed to identify factors significantly associated with the overall duration and total case number of the outbreaks. Of the recorded outbreaks, 72.13% (44/61) met the study criteria and had complete data. The paired Wilcoxon signed-rank test indicated that the class closure group demonstrated fewer new cases and fewer affected classes, as well as a shorter time from CDC intervention to outbreak end, compared to the non-class closure group (Z =−3.313,−1.992,−2.392; P = 0.001, 0.046, 0.017, respectively). However, no significant differences were observed in the terminal attack rate or the overall outbreak duration (Z =−1.161,−1.189; P = 0.245, 0.234, respectively). Multivariable linear regression analysis indicated that outbreaks had a lower cumulative number of cases when they were reported by government employees, the outbreak sites had adequate ventilation, the affected institutions were public, especially kindergartens, classes were suspended before CDC intervention, and there were 15 or fewer cases at the time of CDC response. Additionally, outbreaks had a shorter duration when the CDC intervened within 48 h of the first case onset, classes were suspended prior to CDC intervention, and the affected institutions were public, particularly kindergartens and primary schools. Class closure implemented before CDC intervention significantly reduced the number of new cases and affected classes, shortened the time between CDC intervention and the outbreak end, and did not affect the overall outbreak duration or the final attack rate in Xi’an. Factors such as institution type, institution category, reporting channels to the CDC, ventilation conditions within outbreak sites, whether classes were suspended prior to CDC intervention, the number of cases at the time of CDC intervention, and the duration of emergency response were all significantly associated with the effectiveness of class closure measures in preventing and controlling norovirus outbreaks. The optimal timing for class closure is within 48 h of the first case onset, and the most effective intervention occurs when the number of cases during an outbreak is ≤ 15.