Role of Cycle Threshold of RT-PCR in the Prediction of COVID-19 Cases

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Abstract
Objectives: It is currently unclear whether SARS-CoV-2 Cycle threshold (Ct) values could be leveraged to guide patients’ clinical manifestations and management decisions. The present study was undertaken to observe whether RT-PCR Ct values differ in COVID-19 symptomatic and asymptomatic individuals. This study also describes the clinical manifestations and epidemiological characteristics of both groups of patients. Methods: Nasopharyngeal or oropharyngeal swabs of 35,391 clinically suspected COVID-19 patients were collected in VTM and tested in our dedicated COVID-19 diagnostic laboratory for SARS-CoV-2 RT-PCR test. Cycle threshold at day 1 of positive detection was correlated with the presence or absence of the patient’s symptoms. The Ct values were studied sequentially in the collected samples to understand the variation of Ct values with the patient’s first day of diagnosis up to the recovery day. Results: Of 35,391 samples received for RT-PCR, data from 589 COVID-19 diagnosed patients (positivity 1.66%) was analyzed further. Among 589 patients, a total of 178 patients were symptomatic, while 411 were asymptomatic. Ct values obtained in symptomatic individuals (19.26±4.34) were significantly lower than in the asymptomatic (25.96±4.64) individuals (p<0.01). For 38 SARS-CoV-2 positive patients, data from sequential samples submitted to the laboratory was also analyzed. After adjusting for age, gender, co-morbidities, increased cycle threshold was associated with decreased odds of symptoms and in-hospital admission (0.91, CI 0.89– 0.94, p<0.001). Conclusion: Clinical symptoms and laboratory results of RT-PCR (Ct Value) of symptomatic patients with COVID-19 are significantly lower than those without symptoms. Analyzing data from 38 SARS-CoV-2 positive patients’ sequential samples again demonstrated that symptoms correlate with lower Ct values; however, virus clearance took almost the same time in the two groups of individuals. J Microbiol Infect Dis 2021; 11(3):132-139.