Characteristics of a large outbreak arising from a school field trip after COVID-19 restrictions were eased in 2022.

Background: This study analyzed a large outbreak of coronavirus disease 2019 (COVID-19) that occurred during a high school field trip in the Jeonbuk region and aimed to identify risk factors for COVID-19 infection, with the goal of preventing such outbreaks in the future.

Methods: A retrospective cohort study of 737 participants, including 668 students and 69 staff at High School A, was designed to describe the epidemiological characteristics of this large COVID-19 outbreak. Logistic regression analysis was performed to calculate relative risks (odds ratios [ORs]) and 95% confidence intervals (CIs).

Results: There were 190 confirmed cases (174 students, 16 staff), with an attack rate of 25.8%. Small outbreaks were decreasing before the field trip, but this trend reversed after the trip, leading to larger outbreaks. Logistic regression showed an OR of 2.39 (95% CI, 1.66-3.43; p<0.05) for COVID-19 infection among field trip participants. Among them, 11th graders had an OR of 2.32 (95% CI, 1.53-3.52; p<0.05) compared to 10th graders, while no significant risk difference was found within same-grade teams.

Conclusion: There was a high risk for COVID-19 transmission during extracurricular activities with a large number of participants, such as field trips, even after the nationwide Omicron variant epidemic subsided. Even when students are separated into teams and follow different routes, it is challenging to design routes that entirely prevent contact between teams. Thus, programs should be designed carefully, and students with symptoms should be identified before and during the program to isolate them promptly.