Crowded Spaces, Contagious Risks: Comparing COVID-19 Incidence After Outdoor Concerts Among University Members and the Community, Republic of Korea, 2022

Jisun Sung; Jong-Hun Kim

doi:10.3346/jkms.2025.40.e239

Abstract

Background

A university festival, including outdoor concerts, was held from May 2 to 4, 2022, following the relaxation of coronavirus disease 2019 (COVID-19) restrictions in Korea. This study aimed to assess its impact on COVID-19 cases among university members.

Methods

We collected daily COVID-19 case data from university and local government websites and conducted a causal impact analysis using a Bayesian structural time series model.

Results

The analysis revealed a significant increase in cases following the event. From May 6 to 29, 2022, the university recorded an average of 5.8 daily cases (total: 138 cases). In the counterfactual scenario without the event, the estimated number of daily cases was 2.5 to 3.0 (total: 57.1 to 72.0 cases) based on three prediction models. The outdoor concerts were associated with an approximately twofold increase in COVID-19 cases among university members.

Conclusion

Despite a declining trend in community cases, these findings underscore the potential risks of crowded outdoor gatherings in spreading COVID-19 and highlight the need for caution at such events.

INTRODUCTION

The coronavirus disease 2019 (COVID-19) pandemic significantly affected public gatherings worldwide.1 In 2020 and 2021, the Government of the Republic of Korea implemented various public health measures, including social distancing, mask mandates, and gathering restrictions,2 3 4 leading to the cancellation of large-scale events such as outdoor concerts.5 6

Universities transitioned to real-time online classes in 2020 and gradually resumed face-to-face classes with precautions, while large campus events remained suspended or virtual.7 In April 2022, the Korean government eased restrictions under the Post-Omicron Plan,8 9 allowing universities to resume in-person events.

From May 2 to 4, 2022, a university held its first post-pandemic on-site festival, featuring outdoor concerts each evening, with the largest performance on the final night.10 11 Following the festival, a noticeable increase in COVID-19 cases was observed on campus. This study assessed the impact of the university festival, particularly its outdoor concerts, on COVID-19 cases by comparing observed cases among university members with predicted cases based on community incidence trends.

METHODS

Data source

A university in Jangan (District), Suwon (City), Gyeonggi (Province), Korea, enrolled 11,445 undergraduate and graduate students in the first half of 2022. Since February 17, 2022, the university had publicly posted daily updates on the number of confirmed COVID-19 cases via its "University COVID-19 Status" website.12 COVID-19 diagnosis information was collected through the university’s official mobile application, where university members who tested positive for COVID-19 were required to submit a "COVID-19 Self-Report Form" along with official documentation of their test result. These reports were primarily used for administrative absence tracking, and missing reports were assumed to be minimal.

We obtained data on the daily number of confirmed COVID-19 cases on campus from the "University COVID-19 Status" website, covering February 24 to May 29, 2022. This period included the festival (May 2–4, 2022) and extended until May 29, the first day when campus cases dropped to zero after the festival. Additionally, we obtained data on confirmed COVID-19 cases in Jangan (District), Suwon (City), and Gyeonggi (Province) for the same period from the Gyeonggi Infectious Disease Control Center website.13

Overview of the university festival and concert

The university festival was held over three days on a large lawn within the campus, featuring student-run booths and small-scale student performances.10 Each evening, a professional artist concert took place on an outdoor stage set up on the lawn. On the final night, a highly popular artist drew the largest crowd of the festival. To prevent overcrowding, the university installed fences and designated a student-only zone, allowing entry exclusively to students with verified university ID cards. This zone was officially designed to accommodate up to 12,000 attendees. The concert was a standing-only, open-air event lasting approximately 2–3 hours, with mask-wearing recommended. Event videos and photos11 14 showed that on the final night, the designated student zone was at full capacity, while many others gathered outside the fenced area to watch the performance. The crowd actively cheered, jumped, and sang along in close proximity throughout the event.

Case definition

According to the Korea Disease Control and Prevention Agency guidelines, a confirmed COVID-19 case is defined as the detection of severe acute respiratory syndrome coronavirus 2 using real-time reverse transcription-polymerase chain reaction, regardless of clinical characteristics.15 This study did not conduct direct case investigations but instead used publicly available data on the number of confirmed cases diagnosed through these standard procedures.

Statistical analysis

We employed the Causal Impact methodology16 using a Bayesian structural time-series model to estimate the effect of the university festival on the daily number of confirmed COVID-19 cases on campus. This approach compares observed data to a predicted counterfactual, representing expected cases in the absence of the event.16 Three prediction models were built using COVID-19 data from Jangan (District), Suwon (City), and Gyeonggi (Province). Since outdoor concert attendance was officially restricted to university members, we assumed minimal contribution to case increases in the surrounding community.

The university festival, including outdoor concerts, began on May 2, 2022. Given the Omicron variant’s average incubation period of approximately four days in Korea,17 any related increase in cases was expected by May 6. Therefore, the post-event period was set from May 6 to May 29, when campus cases dropped to zero. To train the model, the pre-event period was set from April 1 to May 5. The start date of April 1 was chosen to exclude earlier high case numbers, which could have introduced a general downward trend rather than isolating the festival’s effect. The analysis was conducted using R version 4.2.2 and the ‘CausalImpact’ R package.

Ethics statement

This study analyzed publicly available, de-identified aggregate data from the university and public health websites. No human subjects were involved, and no personally identifiable information was collected. According to the institutional guidelines, Institutional Review Board review was not required.

RESULTS

Between February 24 and May 29, 2022, confirmed COVID-19 cases in Jangan (District), Suwon (City), Gyeonggi (Province) increased rapidly, peaking on March 16 (Fig. 1). This period marked the first Omicron wave in Korea.17 The university campus exhibited a similar trend, with cases peaking slightly earlier on March 14. After a steady decline, a small but noticeable increase in cases was observed following the university festival (Fig. 1). The first peak of this post-festival outbreak occurred on May 9, five days after the large-scale concert on the final night and seven days after the festival began. Subsequent peaks followed at seven-day intervals on May 16 and May 23. The increase in cases following the event was more prominently observed in the dual-axis line graph (Fig. 2A).

Fig. 1

Epidemic curves of coronavirus disease 2019 on a university campus and in the surrounding community from February 24 to May 29, 2022. The red vertical arrow marks the start of the university festival on May 2.

Fig. 2

Impact of outdoor concerts on COVID-19 cases on a university campus. (A) Dual-axis line graphs comparing the COVID-19 epidemic curves on a university campus (orange lines) and in the surrounding community (blue lines) from April 1 to May 29, 2022. The shaded gray areas represent the pre-event periods used for model training in the Causal Impact analysis. (B) Estimated impact of the outdoor concerts on the number of COVID-19 cases on the university campus. Prediction models 1, 2, and 3 are based on the number of COVID-19 cases among university members and in the general populations of Jangan (District), Suwon (City), and Gyeonggi (Province), respectively. The "original" graphs in the first row display observed values (solid line), predicted values (dashed line), and the 95% credible intervals (blue shade) of the predicted values. The "pointwise" graphs in the second row illustrate the difference between observed and predicted data. The "cumulative" graphs in the third row depict the cumulative sum of daily effects.

COVID-19 = coronavirus disease 2019.

During the post-event period (May 6–29, 2022), the university recorded a daily average of 5.8 cases, with a cumulative total of 138 cases. Prediction Model 1 (Fig. 2B, Table 1), which used university and Gyeonggi (Province) data, estimated that without the festival, the university would have experienced a daily average of 2.5 cases and a total of 60.2 cases during the same period. These results suggested the university festival, including outdoor concerts, led to a daily average of 3.2 additional cases (95% credible interval [CI], 0.7–6.0) and a total of 77.8 additional cases (95% CI, 16.3–143.0) over 23 days. In relative terms, the event was associated with a 2.29-fold increase in confirmed COVID-19 cases (95% CI, 1.27–3.38). Similar results were observed in models 2 and 3, which used data from Suwon (City) and Jangan (District), respectively (Fig. 2B, Table 1).

Table 1

The impact of crowding at outdoor concerts on COVID-19 outbreak

Models		No. of COVID-19 cases		Absolute effect (95% CI)	Relative effect (95% CI)	P value^a
Models		Actual	Predicted	Absolute effect (95% CI)	Relative effect (95% CI)	P value^a
Model 1^b
	Daily average	5.8	2.5	3.2 (0.7–6.0)	2.29 (1.27–3.38)	0.006
	Cumulative	138.0	60.2	77.8 (16.3–143.0)
Model 2^b
	Daily average	5.8	2.4	3.4 (0.6–6.2)	2.42 (1.26–3.59)	0.007
	Cumulative	138.0	57.1	80.9 (15.1–147.9)
Model 3^b
	Daily average	5.8	3.0	2.8 (0.2–5.4)	1.93 (1.07–2.81)	0.017
	Cumulative	138.0	72.0	66.4 (4.8–129.5)

COVID-19 = coronavirus disease 2019, CI = credible interval.

^aPosterior probability.

^bModels 1, 2, and 3 are prediction models based on the number of COVID-19 cases among university members and in the general populations of Gyeonggi (Province), Suwon (City), and Jangan (District), respectively.

DISCUSSION

This study quantitatively assessed the increase in COVID-19 cases among university members following a university festival with outdoor concerts, using surveillance data collected through a mobile application.

Crowd gatherings, particularly in high-density spaces, are linked to increased risks of COVID-19 transmission.18 19 20 While outdoor settings generally pose a lower risk, large-scale events such as concerts, festivals, and sporting events can still facilitate virus transmission, particularly when attendees engage in close contact, singing, or cheering.21 Despite the declining trend of the Omicron wave during the study period, our findings indicate that the outdoor concerts led to approximately twofold increase in COVID-19 cases among university members compared to the predicted scenario without the event. The event footage14 suggests that this increase was likely driven by high crowd density, and the spread of respiratory droplets due to prolonged singing and cheering along with the performers, despite the recommendation for mask-wearing. This underscores the importance of maintaining appropriate preventive measures, such as physical distancing and mask-wearing, until the epidemic has substantially subsided and the overall risk is considered minimal, even at outdoor events that may generally be perceived as lower risk.22

On the other hand, at least before the festival with outdoor concerts took place, the resemblance between the COVID-19 epidemic curves of the university and surrounding community (Fig. 1) suggests that universities could serve as sentinel surveillance sites for monitoring and predicting broader community transmission.23 However, when using universities as sentinel surveillance sites, it is essential to consider major campus events, such as festivals, academic term transitions, and vacations. As demonstrated in our study, these events can temporarily alter transmission dynamics and affect surveillance accuracy.

This study has several limitations. First, we did not conduct a formal epidemiological assessment to evaluate the possibility of large-scale close contact during the festival. Instead, exposure risk was inferred based on observed crowding and behaviors. Second, self-reported data from university members may have led to underreporting or misclassification of cases. However, unless this bias was systematically linked to specific time points, it is unlikely to have significantly altered the overall trend. Third, factors such as the exact number of concerts attendees, compliance with mask mandates, and vaccination status were not accounted for in the analysis. Fourth, using general population data as a control group may introduce bias when estimating the event’s impact on university members, who were predominantly in their 20s. Behavioral differences between university members and the general population, including differences in mobility, exposure patterns, and case ascertainment, could lead to an over- or underestimation of the event’s effect. While epidemic curves were examined before analysis, caution is needed when interpreting results.

Despite these limitations, this study provides valuable quantitative evidence of increased COVID-19 cases following a university festival with outdoor concerts, enhancing the understanding of infection risks associated with large outdoor gatherings. As COVID-19 restrictions eased, many outdoor events were held across Korea in 2022. While media reports suggested a rise in COVID-19 cases among individuals who attended these outdoor events, conducting quantitative evaluations was challenging due to lack of specific data. This study is significant as it offers a quantitative assessment of infection risks at outdoor events and a methodology based on existing epidemiological data.

Notes

Disclosure: The authors have no potential conflicts of interest to disclose.

Author Contributions:

Conceptualization: Kim JH.
Data curation: Sung J, Kim JH.
Formal analysis: Sung J, Kim JH.
Methodology: Sung J, Kim JH.
Visualization: Sung J.
Writing - original draft: Sung J.
Writing - review and editing: Sung J, Kim JH.

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