Epidemiological Correlates of Polymerase Chain Reaction Cycle Threshold Values in the Detection of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

Abstract Background Detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has principally been performed through the use of real-time reverse-transcription polymerase chain reaction testing. Results of such tests can be reported as cycle threshold (Ct) values, which may provide semi-quantitative or indirect measurements of viral load. Previous reports have examined temporal trends in Ct values over the course of a SARS-CoV-2 infection. Methods Using testing data collected during a prospective household transmission investigation of outpatient and mild coronavirus disease 2019 cases, we examined the relationships between Ct values of the viral RNA N1 target and demographic, clinical, and epidemiological characteristics collected through participant interviews and daily symptom diaries. Results We found that Ct values are lowest (corresponding to a higher viral RNA concentration) soon after symptom onset and are significantly correlated with the time elapsed since onset (P