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We used daily real-time reverse-transcription polymerase chain reaction (RT-PCR) results from 67 cases of SARS-CoV-2 infection in a household transmission study, conducted April 2020–May 2021, to examine the trajectory of cycle threshold (Ct) values, an inverse correlate of viral RNA concentration. Ct values varied across RT-PCR platforms and by participant age. Specimens collected from children and adolescents had higher Ct values and adults aged ≥50 years showed lower Ct values than adults aged 18–49 years. Ct values were lower on days when participants reported experiencing symptoms, with the lowest Ct value occurring 2–6 days after symptom onset.

We used daily real-time reverse-transcription polymerase chain reaction (rRT-PCR) results from 67 cases of SARS-CoV-2 infection in a household transmission study to examine the trajectory of cycle threshold (Ct) values, an inverse correlate of viral RNA concentration, from nasal specimens collected between April 2020 and May 2021. Ct values varied over the course of infection, across RT-PCR platforms, and by participant age. Specimens collected from children and adolescents showed higher Ct values and adults aged ≥50 years showed lower Ct values than adults aged 18-49 years. Ct values were lower on days when participants reported experiencing symptoms.

The novel coronavirus pandemic incited unprecedented demand for assays that detect viral nucleic acids, viral proteins, and corresponding antibodies. The 320 molecular diagnostics in receipt of FDA emergency use authorization mainly focus on viral detection; however, no currently approved test can be used to infer infectiousness, i.e., the presence of replicable virus. As the number of tests conducted increased, persistent SARS-CoV-2 RNA positivity by RT-PCR in some individuals led to concerns over quarantine guidelines. To this end, we attempted to design an assay that reduces the frequency of positive test results from individuals who do not shed culturable virus. We describe multiplex quantitative RT-PCR (qRT-PCR) assays that detect genomic RNA (gRNA) and subgenomic RNA (sgRNA) species of SARS-CoV-2, including spike (S), nucleocapsid (N), membrane (M), envelope (E), and ORF8. The absolute copy number of each RNA target was determined in longitudinal specimens from a household transmission study. Calculated viral RNA levels over the 14-day follow up period were compared with antigen testing and self-reported symptoms to characterize the clinical and molecular dynamics of infection and infer predictive values of these qRT-PCR assays relative to culture isolation. When detection of sgS RNA was added to the CDC 2019-Novel Coronavirus Real-Time RT-PCR Diagnostic Panel, we found a qRT-PCR positive result was 98% predictive of a positive culture (negative predictive value was 94%). Our findings suggest sgRNA presence correlates with active infection, may help identify individuals shedding culturable virus, and that similar multiplex assays can be adapted to current and future variants.