Comparison of Initial Thoracic CT Images of COVID-19 Patients with Non-Variant, Alpha, Delta, and Omicron Variants: A Retrospective Study

Background: CT findings and Ground glass opacity (GGO) volumes may differ between SARS CoV-2 non-variant, alpha, delta, and omicron variants. Objective: To compare the thoracic CT findings, GGO volumes, and GGOs’ lung uptake rates among patients with COVID-19 variants. Methods: Thoracic CT images of 83 patients with non-variant, 78 patients with alpha variant, 93 patients with delta variant, and 73 patients with omicron variant having positive Real-Time Polymerase Chain Reaction test results were analyzed retrospectively. GGO volumes and lung volumes were calculated by using the Cavalieri Principle. Differences in CT findings, ground-glass opacity volumes, and lung involvement rates between non-variant and variant groups were evaluated. Results: There were significant differences found in the incidence of GGOs (p < 0.001), air bronchogram (p = 0.007), reticulation (p = 0.002) and subpleural lines, and linear opacities (p = 0.034) between non-variant and variant groups. GGO uptake rates (ground glass opacity volumes × 100 ÷ lung volume) were 8.88% in the non-variant, 4.83% in the alpha variant, 3.50% in the delta variant, and 2.02% in the omicron variant. In estimating variant groups, it was determined that the increase in the rate of GGOs in the right lung increased the probability of having an omicron variant, whereas the presence of nodules decreased it. The possibility of the delta variant increased with an increase in the rate of ground glass opacities in the left lung. Conclusion: Thoracic CT findings solely can be helpful in distinguishing COVID-19 variants. Decreased frequency of uptake rates of GGOs suggested that the severity of COVID-19 disease was gradually decreasing.