Correlation between chest CT and RT-PCR testing in India’s second COVID-19 wave: a retrospective cohort study

A novel coronavirus, later designated as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was found to be responsible for a cluster of pneumonia cases originating in Wuhan City, Hubei province, China and the clinical disease caused by it came to be known as COVID-19. Tests in use for diagnosing COVID-19 infection in India included molecular based tests - RT-PCR, TrueNat and CBNAATAs. As COVID-19 primarily targets the lungs, Chest Computed Tomography (CT) would play a crucial role in the diagnosis, evaluation, and management of the disease. Study was done to assess the diagnostic accuracy of chest computed tomography (CT) in clinically suspected COVID - 19 patients using RT-PCR as the reference standard and establish the correlation between CT Severity Score (CTSS) and RT-PCR results. Material: A single centre tertiary care hospital based retrospective cohort suty was performed on 112 clinically suspected COVID - 19 patients between 1st April 2021 and 31st May 2021. Chest CT and RT-PCR tests were performed for all patients at a time interval of no longer than 7 days between the two tests. Patients with prior chronic respiratory illnesses were excluded. The diagnostic performance of Chest CT was evaluated using RT-PCR as the reference standard. The CTSS was calculated for all patients with positive Chest CT findings, and it was correlated with results of the RT-PCR assay. The primary outcome measures were determination of the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of Chest CT using RT-PCR as the standard of reference. The correlation between CTSS and RT-PCR was the secondary outcome. Observation: 85/112 (76%) patients tested positive on the RT-PCR whereas 91/112 (81%) had chest CT findings typical of SARS-CoV2 infection. Chest CT had a sensitivity of 90.6% [95% CI, 82.3% - 95.8%], a specificity of 48.1% [95% CI 28.7% - 68.0%], a PPV of 84.6% [95% CI, 79.2% - 88.8%], a NPV of 61.9% [95% CI, 43.0% - 77.8%] and an accuracy of 80.4% [95% CI, 71.8% - 87.3%]. There was a significant correlation between the CTSS and RT-PCR positivity (p value = 0.003) Conclusion: Chest CT has a good sensitivity in detecting COVID-19 pneumonia and is useful for moderate to-severe COVID-19 cases in resource limited settings, where RT-PCR testing is cumbersome due to lack of personnel, time, and diagnostic kits.