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Cycle Threshold Values in the Context of Multiple RT-PCR Testing for SARS-CoV-2
Daniel Romero-Alvarez1, Daniel Garzon-Chavez2, Franklin Espinosa3
1Biodiversity Institute and Department of Ecology & Evolutionary Biology, University of Kansas, Lawrence, KS, USA.
Risk Management and Healthcare Policy
|April 7, 2021
Summary
Cycle threshold (Ct) values in RT-PCR tests can indicate COVID-19 infectiousness. Hospitalized patients may remain infectious longer than current isolation guidelines suggest, highlighting the need for Ct value integration in patient management.
Area of Science:
- Virology
- Infectious Diseases
- Molecular Diagnostics
Background:
- Accurate interpretation of reverse transcription polymerase chain reaction (RT-PCR) is crucial for managing coronavirus disease 2019 (COVID-19) cases.
- Current RT-PCR interpretation relies on positive/negative amplification, not quantification of cycle threshold (Ct) values, which may reflect patient infectiousness.
Purpose of the Study:
- To measure Ct values in hospitalized COVID-19 patients over time.
- To assess the implications of Ct values for diagnosis, patient follow-up, and infectiousness.
Main Methods:
- An observational study involving 118 hospitalized Hispanic patients with confirmed COVID-19 in Quito, Ecuador.
- Multiple RT-PCR tests were conducted on deep nasal swab samples, assessing SARS-CoV-2 N, RdRP, and E genes.
Main Results:
- Mean Ct values increased over time, from 29.13 (first test) to 36.12 (fourth test).
- The time to lack of RT-PCR amplification was 34 days, while time to Ct values >33 was 30 days.
- 11% of patients persisted with potentially infectious Ct values beyond current isolation recommendations.
Conclusions:
- Cycle threshold values offer potential for improved COVID-19 diagnosis, management, and control strategies.
- Hospitalized patients may have prolonged periods of potential infectiousness, necessitating a re-evaluation of isolation durations.
