Epidemiol Health.  2020;42(1):e2020047. 10.4178/epih.e2020047.

Time-variant reproductive number of COVID-19 in Seoul, Korea

• Moon SG
• Kim YK
• Son WS
• Kim JH
• Choi J
• Na BJ
• Park B
• Choi BY

• KMID: 2512753
• DOI: http://doi.org/10.4178/epih.e2020047

Abstract

OBJECTIVES
To estimate time-variant reproductive number (R_t) of coronavirus disease 19 based on either number of daily confirmed cases or their onset date to monitor effectiveness of quarantine policies.
METHODS
Using number of daily confirmed cases from January 23, 2020 to March 22, 2020 and their symptom onset date from the official website of the Seoul Metropolitan Government and the district office, we calculated R_t using program R’s package “EpiEstim”. For asymptomatic cases, their symptom onset date was considered as -2, -1, 0, +1, and +2 days of confirmed date.
RESULTS
Based on the information of 313 confirmed cases, the epidemic curve was shaped like ‘propagated epidemic curve’. The daily R_t based on R_{t_c} peaked to 2.6 on February 20, 2020, then showed decreased trend and became <1.0 from March 3, 2020. Comparing both R_t from R_{t_c} and from the number of daily onset cases, we found that the pattern of changes was similar, although the variation of R_t was greater when using R_{t_c}. When we changed assumed onset date for asymptotic cases (-2 days to +2 days of the confirmed date), the results were comparable.
CONCLUSIONS
R_t can be estimated based on R_{t_c} which is available from daily report of the Korea Centers for Disease Control and Prevention. Estimation of R_t would be useful to continuously monitor the effectiveness of the quarantine policy at the city and province levels.

Keyword

COVID-19; Communicable disease; Epidemics; Seoul