Fig. 2.

a Group A, usual distribution. Chest radiography of a 78-year-old man, acquired within the first 2 days since the onset of symptoms, showing bilateral reticular alteration in the middle and lower fields (arrows). b Group B, usual distribution. Chest radiography of a 79-year-old woman, acquired within 3–5 days since the onset of symptoms, showing bilateral peripheral ground-glass opacities (arrows) and faint reticular alteration in the right lower field. c Group C, usual distribution. Chest radiography of a 60-year-old woman, acquired within 6–9 days since the onset of symptoms, showing bilateral and symmetrical mixed patterns with ground-glass opacification, patchy consolidations (arrows); reticular alteration in the right lower and middle fields. d Group D, usual distribution. Chest radiography of a 61-year-old woman, acquired after 10 days since the onset of symptoms, showing bilateral and symmetrical extensive consolidations (arrows)