Results

Patient demographics
Of 88 patients in the study cohort, 51 (58.0%) were male and 37 (42.0%) were female; mean age was 42.7 years (range, 4–82 years). Fifty-three (60.2%) patients had 2 CTs, 24 (27.2%) had 3 CTs, and 11 (12.5%) had 4 or more CTs. The mean time interval between symptom onset and baseline CT was 5.5 ± 3.5 days (range, 1–15 days). Five (5.7%) patients in the study cohort were known to have been discharged from the hospital. All of the patients had mild pneumonia based on the WHO definition [10].
The demographics of the study cohort are detailed in Table 1. Patients with exposure history (recent travel to Wuhan or contact with infected patient) accounted for 85.2% of study cohort. Fever (84.1%) and cough (56.8%) were the most common presenting symptoms. Low lymphocyte and white cell counts were observed in 26.4% and 25.0% of patients, while high C-reactive protein was observed in 55.0% of patients.
Table 1 Patient demographics and laboratory test results
Characteristic Patient with NCP (n = 88)
Age (years)a 42.7 ± 14.5
Age group (years)
  < 15 2 (2.3)
  15–44 48 (54.5)
  45–64 28 (31.8)
  ≥ 65 10 (11.4)
Male sex 51 (58.0)
Exposure history
  Recent travel to Wuhan 45 (51.1)
  Contact with infected patient 30 (34.1)
  Unknown exposure 13 (14.8)
Initial symptoms
  Fever 74 (84.1)
  Cough 50 (56.8)
  Expectoration 19 (21.6)
  Fatigue 15 (17.0)
  Chest distress and/or shortness of breath 12 (13.6)
  Pharyngalgia 10 (11.4)
  Muscle soreness 7 (8.0)
  Headache 5 (5.7)
  Nausea and/or vomiting 0 (0)
  Diarrhea 0 (0)
  No obvious symptoms 3 (3.4)
Laboratory testing at initial hospital visitb
  White blood cell count (–, ↑, ↓) 62 (70.5), 4 (4.5), 22 (25.0)
  Lymphocyte count (–, ↑, ↓) 62 (71.3), 2 (2.3), 23 (26.4)
  Percent lymphocytes (–, ↑, ↓) 55 (62.5), 7 (8.0), 26 (29.5)
  Percent neutrophilic granulocyte (–, ↑, ↓) 59 (67.1), 17 (19.3), 12 (13.6)
  Percent monocytes (–, ↑, ↓) 59 (67.1), 26 (29.5), 3 (3.4)
  Hemoglobin (–, ↑, ↓) 68 (77.3), 8 (9.1), 12 (13.6)
  ALT (–, ↑, ↓) 70 (79.5), 16 (18.2), 2 (2.3)
  AST (–, ↑, ↓) 73 (83.0), 15 (17.0), 0 (0)
  Creatine kinase (–, ↑, ↓) 73 (84.9), 4 (4.6), 9 (10.5)
  C-reactive protein (–, ↑, ↓) 36 (45.0), 44 (55.0), 0 (0)
Unless otherwise indicated, data are reported as the number of patients, with percentages in parentheses
ALT alanine aminotransferase, AST aspartate aminotransferase
aData are reported as the mean ± standard derivation
bThe signs –, ↑, and ↓ represent within, above, and below normal ranges of laboratory results, respectively. Normal ranges of white blood cell count, lymphocyte count, percent lymphocytes, percent neutrophilic granulocyte, percent monocytes, ALT, AST, creatine kinase, hemoglobin, and C-reactive protein were 3.5–9.5 × 109/L, 1.10–3.20 × 109/L, 20–50%, 3.0–10.0%, 40–75%, 115–150 g/L, 7–40 U/L, 13–35 U/L, 40–200 U/L, and 0–10 mg/L, respectively

Evolution of CT findings in patients with COVID-19

Evolution of CT characteristics of pulmonary lesions
Figure 1 depicts the evolution of CT features of pulmonary lesions in different time intervals from disease onset. Significant differences were found among the time intervals in the proportion of pulmonary lesions that are (1) pure GGO (χ2 = 37.97, p = 0.01), (2) mixed attenuation (GGO and consolidation) (χ2 = 12.80, p < 0.01), (3) mixed attenuation with reticular/linear opacities (χ2 = 20.57, p < 0.01), and (4) consolidation with reticular/linear opacities (χ2 = 32.49, p < 0.01) and pure consolidation (χ2 = 10.37, p = 0.03). A significant linear decrease in the proportions of pure GGO lesions (y = 0.55–0.08x, p < 0.01) and mixed attenuation lesions (y = 0.31–0.03x, p = 0.01) and a significant linear increase in the proportions of lesion with reticular/linear opacities (mixed attenuation + linear opacities (y = 0.08 + 0.04x, p < 0.01) and consolidation + linear opacities (y = − 0.03 + 0.04x, p < 0.01)) were observed over time.
Fig. 1 Evolution of CT characteristics of pulmonary lesions in patients with COVID-19. The time intervals after disease onset (days) were divided into 5 groups, i.e., days 0–3 (lesion number = 114), days 4–7 (lesion number = 241), days 8–10 (lesion number = 189), days 11–14 (lesion number = 178), and days 15–21 (lesion number = 95). GGO, ground glass opacities; mixed attenuation = ground glass opacities + consolidation

Evolution of lobar distribution in patients with COVID-19
No statistically significant difference was found in the lobar distribution of pulmonary findings over different time intervals from symptom onset, but some trends were observed. For example, the proportion of patients with fewer than 3 lobes affected decreased in the first 10 days (Fig. 2a). The proportion of patients with three or more affected lobes was higher in all of the time intervals analyzed. Bilateral involvement was more prevalent than unilateral involvement with a trend toward an increase in the proportion of patients with bilateral CT abnormalities in the first 2 weeks after disease onset (Fig. 2b). Lower lobes have higher rates of involvement than the others, but the differences are not statistically significant (Fig. 2c).
Fig. 2 Evolution of lobar distribution of the (a) number of lobe affected, (b) unilateral and bilateral lobes affected, and (c) lung lobe affected in patients with COVID-19 within 21 days after disease onset. The time after disease onset (day) is categorized as 5 groups, i.e., days 0–3 (patient number = 37), days 4–7 (patient number = 69), days 8–10 (patient number = 53), days 11–14 (patient number = 49), and days 15–21 (patient number = 25)

Evolution of CT findings in patients with COVID-19
The initial CTs of 4 out of 88 (4.5%) patients were negative. Two of these four patients had their baseline CT during days 1–3, one during days 4–7, and one during days 8–10 of disease. Subsequently, CT images of one patient remained negative even during days 8–10, and other patients developed CT abnormalities.
There were significant differences between the time interval groups after disease onset in proportions of patients with both GGO and consolidation (χ2 = 22.2, p < 0.01) and the combination of GGO, consolidation, and linear opacities (χ2 = 21.5, p < 0.01) (Table 2). A proportion of patients with GGO and consolidation presented a decreasing trend during the 21 days after disease onset (y = 0.48–0.09x, p < 0.01), while a proportion of patient with all three findings including ground glass opacities, consolidation, and linear opacities presented an increasing trend (y = 0.12–0.11x, p < 0.01). No significant difference was found in the proportions of patients with other CT findings or total lung severity score.
Table 2 Evolution of CT findings and total lung severity scores of patients with COVID-19 within 21 days after disease onset
Characteristic Time after disease onset χ2 p value
Days 0–3 (n = 37) Days 4–7 (n = 69) Days 8–10 (n = 53) Days 11–14 (n = 49) Days 15–21 (n = 25)
Pulmonary opacities
  GGO only 8 (21.6) 13 (18.8) 7 (13.2) 4 (8.2) 1 (4.0) 6.6 0.16
  GGO and consolidation 12 (32.4) 26 (37.7) 8 (15.1) 5 (10.1) 1 (4.0) 22.2 < 0.01
  GGO and linear opacities 2 (5.4) 2 (2.9) 4 (7.5) 2 (4.1) 2 (8.0) 1.87 0.76
  Consolidation only 1 (2.8) 6 (8.7) 3 (5.7) 4 (8.2) 1 (4.0) 1.98 0.74
  Consolidation and linear opacities 0 (0) 2 (2.9) 4 (7.5) 4 (8.2) 3 (12.0) 6.0 0.19
  GGO, consolidation, and linear opacities 12 (32.4) 19 (27.5) 25 (47.2) 30 (61.2) 17 (68.0) 21.5 < 0.01
  Negative CT 2 (5.4) 1 (1.5) 2 (3.8) 0 (0.0) 0 (0.0) 4.3 0.36
Other findings
  Discrete pulmonary nodules 4 (10.8) 4 (5.8) 3 (5.7) 1 (2.0) 0 (0) 4.8 0.36
  Pleural effusion 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) – –
  Lymphadenopathy 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) – –
  Cavitation 3 (8.1) 3 (4.3) 1 (1.9) 2 (4.1) 1 (4.0) 2.1 0.72
Total lung severity score
  Mean ± SD 3.9 ± 2.7 4.8 ± 2.9 4.9 ± 2.8 5.3 ± 3.3 5.2 ± 2.8 – 0.29
  Median (range) 4 (0–10) 5 (0–12) 5 (0–11) 5 (1–13) 5 (1–11) – –
Numbers in parentheses are percentages
n number of patients, GGO ground glass opacities
None of the patients had pleural effusions or intrathoracic lymphadenopathy during the follow-up period. Some of the patients had cavitation on CT, but these are thought to represent pre-existing conditions as none of the patients in the study cohort developed cavitation on follow-up CT.
Figures 3 and 4 show the evolution of CT findings of two patients with COVID-19 pneumonia.
Fig. 3 A 54-year-old woman with exposure to a COVID-infected patient presented with fever, cough, and low back pain for 2 days and remains hospitalized. a–c CT shows left lower lobe GGO on day 2. The total severity score is 1. d–f CT on day 7 shows a significant increase in GGO in both lungs. The severity score of the left lower lobe is 2. The total severity score is 5. g–i CT on day 9 shows bilateral GGO and subpleural consolidation. The severity score of the left lower lobe is 3. The total severity score is 9. j–l CT on day 11 shows diffuse GGO and linear opacities (thick arrow). The severity score of the left lower lobe is 4. The total severity score is 12
Fig. 4 A 24-year-old man with exposure to a COVID-infected patient presented with fever and cough for 1 day and remains hospitalized currently. a–e CT scan shows GGO in the subpleural left lower lobe on day 1 (thick arrow). The overall total severity score is 1. f–j CT on day 4 shows enlarging GGO in left lower lobes (thick arrow). The overall total severity score is 3. k–o CT on day 8 shows increased GGO in bilateral lower lobes. The total severity score was 5. p–t CT obtained on day 11 shows bilateral ground glass opacities and linear opacities (thick arrow). The overall total severity score was 7. u–y CT obtained on day 15 shows improvement of bilateral lower lobe GGO and atoll sign (thick arrow). The overall total severity score is 5