Correlation of RT-PCR Cycle Threshold Value and Chest Computed Tomography Scan Severity Score in Patients with COVID-19: A Cross-sectional Study

Abstract

Introduction: Chest Computed Tomography (CT) scan for Coronavirus Disease-2019 pneumonia is used widely and viral load is predicted by the Cycle threshold (Ct) values of Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR). Studies correlating viral load in Severe Acute Respiratory SyndromeCoronavirus-2 (SARS-CoV-2) RT-PCR positive patients and severity of chest CT scan are limited. Aim: To find an association between viral load and chest CT findings. Materials and Methods: This was a cross-sectional study conducted on patients admitted to Believers Church Medical College Hospital, Thiruvalla, Kerala between September 2020 to March 2021. TrueNat RT-PCR test was performed on nasopharyngeal swabs, targeting the Orf1 gene of SARS-CoV-2 and results were quantified as Cycle threshold (Ct) values. Chest CT-Total Severity Score (TSS) ranged from 0-40 and was calculated by summing up the acute inflammatory lesions in each of the five lobes of both the lungs. Correlation was assessed using Spearman's Correlation Coefficient. Independent sample t-test and one-way Analysis of Variance (ANOVA) were used for comparison of means. Results: Of the 102 patients in the study [mean age of the patients 64.13±13.17 years and majority were males (70.6%)], 11 had lung changes unrelated to COVID-19. There was an inverse relationship between viral load Ct value of SARS-CoV-2 in nasopharyngeal specimens and TSS of chest CT scan. The mean viral load was highest in patients with mild (21.48±8.31), moderate (21.22±6.30) and severe (24.19±4.67) CT involvement. There was a significant difference between mean duration to symptom onset and chest CT scan among those with a high viral load (4.97±2.65) compared to those with a low viral load (6.81±4.5), (p-value=0.01). Among those who died due to COVID-19, (12/13) 92.3% were above 60 years of age. Presence of co-morbidities/dyspnoea/fever at presentation did not have any significant association with TSS severity. Conclusion: Viral load is not a critical factor that influences pulmonary manifestations in COVID-19, nor in-hospital mortality. CT scan may be more useful to detect lung involvement when done nearing or after the first week of symptom onset, irrespective of the viral load. Viral load can be important in predicting transmissibility and to minimise potential spread, whereas chest CT can help identify cases requiring extensive medical care.

Keywords

• computed tomography
• coronavirus disease-2019
• reverse transcriptase-polymerase chain reaction
• total severity score
• viral load