Data collection and evaluation
The medical records of patients were reviewed to determine the demographic data, medical history, exposure history, clinical symptoms, laboratory findings, and time of disease onset. The date of disease onset was defined as patients’ reported date of symptom onset. The time intervals, in days, between each CT scan and disease onset were determined and categorized into five groups (days 0–3, days 4–7, days 8–10, days 11–14, and days 15–21).
CT images were reviewed independently by two thoracic radiologists each with 10 years of experience. Differences were resolved by discussion to reach consensus. Similar to a previously published report [6], CT findings including the presence and distribution of ground glass opacities (GGO), consolidation, linear opacities, discrete pulmonary nodules, pleural effusion, lymphadenopathy, and cavitation were evaluated. Degree of lobar involvement and overall lung total severity score were recorded. Each of the five lung lobes was assessed for degree or area of involvement and assigned a score of 0 for 0% lobe involvement, 1 for 1–25% lobe involvement, 2 for 26–50% lobe involvement, 3 for 51–75% lobe involvement, or 4 for 76–100% lobe involvement. An overall lung total severity score was reached by summing the five lobe scores (range of possible scores, 0–20) [5].