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Brief Report
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, Sanggu Kang, Boeun Kim, Yong Jin Gil, Seung-sik Hwang, Sung-il Cho
J Prev Med Public Health. 2023;56(4):377-383.   Published online June 21, 2023
DOI: https://doi.org/10.3961/jpmph.23.056
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AbstractAbstract AbstractSummary PDFSupplementary Material
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.
Summary
Korean summary
“3T”전략과 “3C”전략으로 대표되는 한국과 일본의 코로나 19 유행 시기의 NPI 정책을 비교하고, 접촉자 추적 및 검사 역량의 지표로 감염경로를 알 수 없는 확진자(unlinked case)와 검사 양성률(TPR)의 역할을 평가하였다. 감염경로를 알 수 없는 확진자(UC)는 전체 확진자수 증가 및 검사 양성률의 증가와 관련이 있었으며, 이는 COVID-19 통제에 있어 검사와 접촉자 추적을 적절히 조합하는 것이 중요함을 보여준다.

JPMPH : Journal of Preventive Medicine and Public Health