J Korean Med Sci.  2020 Aug;35(31):e288. 10.3346/jkms.2020.35.e288.

Epidemiological Characteristics of COVID-19 Outbreak at Fitness Centers in Cheonan, Korea

• Bae S
• Kim H
• Jung TY
• Lim JA
• Jo DH
• Kang GS
• Jeong SH
• Choi DK
• Kim HJ
• Cheon YH
• Chun Mk
• Kim M
• Choi S
• Chun C
• Shin SH
• Kim HK
• Park YJ
• Park O
• Kwon HJ

• KMID: 2505202
• DOI: http://doi.org/10.3346/jkms.2020.35.e288

Abstract

Background
In February 2020, a coronavirus disease 2019 (COVID-19) outbreak was reported in fitness centers in Cheonan, Korea.
Methods
From February 24 to March 13, an epidemiological investigation was conducted on the fitness center outbreak. All those who were screened were tested for severe acute respiratory syndrome coronavirus-2 (SARS CoV-2) using real-time reverse transcriptase polymerase chain reaction. Contacts were traced and self-isolated for 14 days. We determined the epidemiological characteristics of confirmed cases of SARS-CoV-2 infection, and estimated the time-dependent reproduction number to assess the transmission dynamics of the infection.
Results
A total of 116 cases were confirmed, and 1,687 contacts were traced. The source cases were 8 Zumba instructors who led aerobics classes in 10 fitness centers, and had the largest average number of contacts. A total of 57 Zumba class participants, 37 of their family members, and 14 other contacts were confirmed as cases. The attack rate was 7.3%. The contacts at Zumba classes and homes had a higher attack rate than other contacts. The mean serial interval (± standard deviation) were estimated to be 5.2 (± 3.8) days. The time-dependent reproduction number was estimated to be 6.1 at the beginning of the outbreak, but it dropped to less than 1, 2 days after the epidemiological investigation was launched.
Conclusion
The results suggest that the COVID-19 outbreak was effectively contained with rigorous contact tracing, isolating, and testing in combination with social distancing without a lock-down.

Keyword

Coronavirus; Disease Outbreak; Epidemiology; Basic Reproduction Number; Fitness Centers

Figure

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  Fig. 1 Distributions of estimated incubation periods of coronavirus disease 2019 in fitness center outbreak in Cheonan. Maximum period was calculated by substracting earliest contact date from incidence date. Minimum period was calculated by substracting latest contact date from incidence date.

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  Fig. 2 Epidemiological characteristics of COVID-19 outbreak in fitness center in Cheonan, Korea. (A) Epidemic curve. (B) Trend of the number of the people tested for COVID-19 and diagnosed. (C) Time dependent reproduction number (Rt) and 95% confidence interval (grey area).On Feb. 18th, the patient 31 was diagnosed, and on Feb. 23rd, the National Alert level was elevated to Serious (Red). On Feb. 24 (red vertical line), the fitness centers outbreak was identified, and the contact tracing and isolation began.COVID-19 = coronavirus disease 2019.

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  Fig. 3 Distribution of period between diagnosis and symptom onset of coronavirus disease 2019 outbreak in fitness centers in Cheonan, Korea.

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