Population-level median cycle threshold (Ct) values for asymptomatic COVID-19 cases can predict the trajectory of future cases

Abstract

Background Recent studies indicate that the population-level SARS-CoV-2 cycle threshold (Ct) values can inform the trajectory of the pandemic. The presented study investigates the potential of Ct values in predicting the future of COVID-19 cases. We also determined whether the presence of symptoms could change the correlation between Ct values and future cases. Methods We examined the individuals (n = 8660) that consulted different sample collection points of a private diagnostic center in Pakistan for COVID-19 testing between June 2020 and December 2021. The medical assistant collected clinical and demographic information. The nasopharyngeal swab specimens were taken from the study participants and real-time reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect SARS-CoV-2 in these samples. Results We observed that median Ct values display significant temporal variations, which show an inverse relationship with future cases. The monthly overall median Ct values negatively correlated with the number of cases occurring one month after specimen collection (r = -0.588, p <0.05). When separately analyzed, Ct values for symptomatic cases displayed a weak negative correlation (r = -0.167, p<0.05), while Ct values from asymptomatic cases displayed a stronger negative correlation (r = -0.598, p<0.05) with the number of cases in the subsequent months. Predictive modeling using these Ct values closely forecasted the increase or decrease in the number of cases of the subsequent month. Conclusions Decreasing population-level median Ct values for asymptomatic COVID-19 cases appear to be a leading indicator for predicting future COVID-19 cases.

Cycle Threshold Values as Indication of Increasing SARS-CoV-2 New Variants, England, 2020–2022

“…Smaller studies have suggested that changes in Ct values can indicate changes in trajectory of the epidemic, including a study from Spain ( 33 ) that reported differential changes in mean Ct values and rate of positive tests in the first and second waves; a study from Pakistan ( 34 ), a study from Italy ( 35 ), and a study from Belgium ( 36 ) that reported a 17-day lag between changes in Ct values and positive tests, and a study from the United States that reported a 33-day lag between Ct values and cases ( 37 ). Our study, which used national surveillance data for >1 year, along with studies from ONS CIS and other studies in the United Kingdom ( 4 , 28 ) (A.S. Walker AS, unpub.…”