Journal of Medicine and Life Science

Institute for Medical Science (제주대학교 의과학연구소)
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Epidemiological application of the cycle threshold value of RT-PCR for estimating infection period in cases of SARS-CoV-2

  • Soonjong Bae (WHO Health Emergencies Programme, WHO Western Pacific Regional Office) ;
  • Jong-Myon Bae (Jeju Center for Infectious Diseases Control and Prevention)
  • Received : 2023.05.18
  • Accepted : 2023.09.04
  • Published : 2023.09.30
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Abstract

Epidemiological control of coronavirus disease 2019 (COVID-19) is needed to estimate the infection period of confirmed cases and identify potential cases. The present study, targeting confirmed cases for which the time of COVID-19 symptom onset was disclosed, aimed to investigate the relationship between intervals (day) from symptom onset to testing the cycle threshold (CT) values of real-time reverse transcription-polymerase chain reaction. Of the COVID-19 confirmed cases, those for which the date of suspected symptom onset in the epidemiological investigation was specifically disclosed were included in this study. Interval was defined as the number of days from symptom onset (as disclosed by the patient) to specimen collection for testing. A locally weighted regression smoothing (LOWESS) curve was applied, with intervals as explanatory variables and CT values (CTR for RdRp gene and CTE for E gene) as outcome variables. After finding its non-linear relationship, a polynomial regression model was applied to estimate the 95% confidence interval values of CTR and CTE by interval. The application of LOWESS in 331 patients identified a U-shaped curve relationship between the CTR and CTE values according to the number of interval days, and both CTR and CTE satisfied the quadratic model for interval days. Active application of these results to epidemiological investigations would minimize the chance of failing to identify individuals who are in contact with COVID-19 confirmed cases, thereby reducing the potential transmission of the virus to local communities.

Keywords

Acknowledgement

We deeply appreciate the staff of the infectious disease team in six community health centers in Jeju Province who performed epidemiological investigations on confirmed cases of COVID-19; the RT-PCR test staff of the Jeju Institute of Health and Environment who conducted RT-PCR tests to confirm COVID-19; and the staff of Team for Infection Control of Jeju Province Office who analyzed epidemiological investigation reports and decided on the countermeasures.

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