| Microorganisms | COPD | Non-COPD | p-value |
| Subjects n | 212 | 1167 | |
| No diagnosis | 117 (55.2) | 630 (54.0) | 0.74 |
| Diagnosis | 95 (44.8) | 537 (46.0) | |
| Streptococcus pneumoniae | 36 (37.9) | 230 (42.8) | 0.37 |
| Virus spp.# | 13 (13.7) | 67 (12.5) | 0.74 |
| Legionella pneumophila | 2 (2.1) | 42 (7.8) | 0.04 |
| Staphylococcus aureus | 0 (0.0) | 17 (3.2) | 0.08 |
| Chlamydophila pneumoniae | 2 (2.1) | 22 (4.1) | 0.35 |
| Mycoplasma pneumoniae | 2 (2.1) | 18 (3.4) | 0.52 |
| Haemophilus influenzae | 1 (1.1) | 12 (2.2) | 0.45 |
| Pseudomonas aeruginosa | 7 (7.4) | 5 (0.9) | <0.01 |
| Klebsiella pneumoniae | 0 (0.0) | 5 (0.9) | 1.00 |
| Moraxella catarrhalis | 0 (0.0) | 2 (0.4) | 1.00 |
| Escherichia coli | 2 (2.1) | 7 (1.3) | 0.54 |
| Others | 12 (12.6) | 42 (7.8) | 0.12 |
| Polymicrobial pneumonia¶ | 18 (18.9) | 68 (12.7) | 0.10 |
Data are presented as n (%), unless otherwise stated. p-values in bold indicate statistical significance. #: influenza A, influenza B, parainfluenza virus, respiratory syncytial virus and adenovirus. ¶: two microorganisms were found in 16 patients and three microorganisms were found in two patients in the COPD group; two microorganisms were found in 61 patients and three microorganisms were found in seven patients in the non-COPD group.