Cycle threshold values in RT-PCR to determine dynamics of SARS-CoV-2 viral load: An approach to reduce the isolation period for COVID-19 patients.

Abstract

Severe acute respiratory syndrome coronavirus (SARS‐CoV‐2) has affected all inhabited continents, and India is currently experiencing a devastating second wave of coronavirus disease‐2019 (COVID‐19). Here, we examined the duration of clearance of SARS‐CoV‐2 in respiratory samples from 207 infected cases by real‐time reverse‐transcription polymerase chain reaction (RT‐PCR). A substantial proportion of COVID‐19 positive cases with cycle threshold (Ct) values more than or equal to 31 (45.7%) were subsequently tested negative for SARS‐CoV‐2 RNA within 7 days of initial detection of the viral load. A total of 60% of all the patients with COVID‐19, irrespective of their Ct values, cleared SARS‐CoV‐2 RNA within 14 days of the initial detection. Longitudinal assessment of RT‐PCR test results in individuals requiring 15–30 days to clear SARS‐CoV‐2 RNA showed a significant reduction of the viral load in samples with high or intermediate viral loads (Ct values ≤ 25 and between 26 and 30, respectively) but the follow‐up group with low viral RNA (Ct values ≥ 31) exhibited a stable viral load. Together, these results suggest that COVID‐19 positive cases with Ct values more than or equal to 31 require reduced duration to clear SARS‐CoV‐2, and thus, a shorter isolation period for this group might be considered to facilitate adequate space in the COVID Care Centres and reduce the burden on healthcare infrastructure.