Journal of Preventive Medicine and Public Health

The Korean Society for Preventive Medicine (대한예방의학회)
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Utilization of the Unlinked Case Proportion to Control COVID-19: A Focus on the Non-pharmaceutical Interventional Policies of the Korea and Japan

  • Yeri Jeong (Department of Preventive Medicine, Graduate School of Public Health, Seoul National University) ;
  • Sanggu Kang (Department of Preventive Medicine, Graduate School of Public Health, Seoul National University) ;
  • Boeun Kim (Graduate School of Public Health, Seoul National University) ;
  • Yong Jin Gil (Department of Preventive Medicine, Graduate School of Public Health, Seoul National University) ;
  • Seung-sik Hwang (Department of Preventive Medicine, Graduate School of Public Health, Seoul National University) ;
  • Sung-il Cho (Department of Public Health Science, Graduate School of Public Health, Seoul National University)
  • Received : 2023.01.31
  • Accepted : 2023.05.11
  • Published : 2023.07.31
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Abstract

Objectives: Korea and Japan have managed the spread of coronavirus disease 2019 (COVID-19) using markedly different policies, referred to as the "3T" and "3C" strategies, respectively. This study examined these differences to assess the roles of active testing and contact tracing as non-pharmaceutical interventions (NPIs). We compared the proportion of unlinked cases (UCs) and test positivity rate (TPR) as indicators of tracing and testing capacities. Methods: We outlined the evolution of NPI policies and investigated temporal trends in their correlations with UCs, confirmed cases, and TPR prior to the Omicron peak. Spearman correlation coefficients were reported between the proportion of UCs, confirmed cases, and TPR. The Fisher r-to-z transformation was employed to examine the significance of differences between correlation coefficients. Results: The proportion of UCs was significantly correlated with confirmed cases (r=0.995, p<0.001) and TPR (r=0.659, p<0.001) in Korea and with confirmed cases (r=0.437, p<0.001) and TPR (r=0.429, p<0.001) in Japan. The Fisher r-to-z test revealed significant differences in correlation coefficients between the proportion of UCs and confirmed cases (z=16.07, p<0.001) and between the proportion of UCs and TPR (z=2.12, p=0.034) in Korea and Japan. Conclusions: Higher UCs were associated with increases in confirmed cases and TPR, indicating the importance of combining testing and contact tracing in controlling COVID-19. The implementation of stricter policies led to stronger correlations between these indicators. The proportion of UCs and TPR effectively indicated the effectiveness of NPIs. If the proportion of UCs shows an upward trend, more testing and contact tracing may be required.

Keywords

Acknowledgement

This study was supported by funds from the Seegene Medical Foundation (grant No. 200-20210107).

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