Association of epidemiological and clinical features with PCR cycle threshold values of SARS-CoV-2 infection: a cross-sectional study

ABSTRACT

The cycle threshold (Ct) in quantitative real-time reverse-transcriptase polymerase chain reaction (qRT-PCR) is inversely correlated to the amount of viral nucleic acid or viral load and can be regarded as an indicator of infectivity. We examined the association of socio-demographic and clinical characteristics of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) polymerase chain reaction (PCR) positive cases with PCR cycle threshold (Ct) values at the time of diagnosis. SARS-CoV-2 cases reported between 12 October 2020 and 24 January 2021 in Regensburg were analyzed employing bivariate and multivariable methods. We included 3,029 SARS-CoV-2 cases (31% asymptomatic at diagnosis) and analyzed the association of case characteristics with Ct values in 2,606 cases. Among symptomatic patients, cough (38.0%), rhinitis (32.4%), headache (32.0), and fever/chills (29.9%) were the most frequent complaints. Ct values ≤20 were more frequent in symptomatic cases (20.9% vs. 11.3%), whereas Ct values >30 were more common in asymptomatic cases (32.6% vs. 18.0%). Ct values >20 and ≤30 were most common in symptomatic and asymptomatic cases (48.0% vs 40.7%). We observed lower median Ct values of E and N gene in symptomatic cases. In a random forest model, the total number of symptoms, respiratory symptoms, and age were most strongly associated with low Ct values. In conclusion, certain symptoms and age were associated with lower Ct values. Ct values can be used as a pragmatic approach in estimating infectivity at the first notification of a case and, thus, in guiding containment measures.

KEYWORDS:

• COVID-19
• symptoms
• Ct value
• asymptomatic cases
• epidemiology

Acknowledgements

We thank the members of our contact-tracing team for collecting the data.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/20477724.2022.2158003

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethics approval and consent to participate

The study was approved by the ethics committee of the University of Regensburg (file number 22-3106-104). All the procedures performed were part of the routine infection control investigations/based on the German Infection Protection Act (Infektionsschutzgesetz, IfSG).

Additional information

Funding

The author(s) reported that there is no funding associated with the work featured in this article.