Trends in SARS-CoV-2 cycle threshold (Ct) values from nucleic acid testing predict the trajectory of COVID-19 waves

Abstract

Forecasting COVID-19 waves helps with public health planning and resource allocation. Cycle threshold (Ct) values obtained from positive SARS-CoV-2 nucleic acid amplification test (NAAT) results offer limited value for individual patient management, but real-time analysis of temporal trends of aggregated Ct values may provide helpful information to predict the trajectories of COVID-19 waves in the community. Ct value trends on 59,609 SARS-CoV-2 NAAT-positive results from 574,403 tests using a single testing assay system, between September 2021 and January 2023, were examined to monitor the trend of the proportion of positive NAAT with lower Ct values (≤28) in relation to changing COVID-19 case numbers over time. We applied regression with autoregressive integrated moving average errors modelling approach to study the relation between Ct values and case counts. We also developed an insight product to monitor the temporal trends with Ct values obtained from SARS-CoV-2 NAAT-positive results. In this study, the proportion of lower Ct values preceded by a range of 7–32 days the rising population COVID-19 testing rate reflecting onset of a COVID-19 wave. Monitoring population Ct values may assist in predicting increased disease activity.