| Baseline characteristics and comorbidities | Study population | CPE/Emp | Uncomplicated pneumonia | p Value |
| No | 1269 | 92 | 1177 | |
| Age (years) | 66 (51–78) | 57 (41–68) | 67 (51–78) | <0.0001 |
| Gender (% male) | 49.2% | 57.6% | 48.5% | 0.1 |
| Chronic cardiac disease | 19.1% | 9.8% | 19.8% | 0.02 |
| Liver disease | 5% | 10.9% | 4.6% | 0.009 |
| Neurological disease | 11.1% | 2.2% | 11.8% | 0.01 |
| Chronic renal failure | 6% | 6.5% | 5.9% | 0.8 |
| Diabetes mellitus | 10.2% | 6.5% | 10.5% | 0.2 |
| COPD | 20.3% | 4.3% | 21.5% | 0.0005 |
| Chronic alcohol abuse | 5.5% | 13% | 4.9% | 0.002 |
| Intravenous drug use | 3% | 10.9% | 2.4% | <0.0001 |
| Current smokers | 34.2% | 44.6% | 33.4% | 0.04 |
The p value is derived from comparison between patients with CPE/Emp and patients with uncomplicated pneumonia using the χ2 test, except for age (Mann–Whitney U test).
COPD, chronic obstructive pulmonary disease; CPE/Emp, complicated parapneumonic effusion or empyema.