| Variables | Patients without pleural effusion | Patients with UPE | Patients with E/CPE | p-values# |
| Subjects n | 3833 | 621 | 261 | |
| Epidemiological data | ||||
| Age yrs | 69 (55–78) | 69 (52–79) | 54 (41–71)# | <0.001 |
| Sex male | 2594 (68) | 396 (64) | 184 (71) | 0.083 |
| Underlying diseases | 2385 (62) | 361 (58) | 118 (45)# | <0.001 |
| COPD | 1009 (26) | 150 (24) | 41 (16)# | 0.001 |
| Diabetes mellitus | 774 (20) | 117 (19) | 44 (17) | 0.341 |
| Heart failure | 808 (21) | 140 (23) | 26 (10)# | <0.001 |
| Chronic liver disease | 210 (6) | 41 (7) | 23 (9) | 0.056 |
| Chronic renal disease | 229 (6) | 34 (6) | 7 (3) | 0.082 |
| Neoplasm | 356 (9) | 43 (7) | 16 (6) | 0.055 |
| Cerebrovascular disease | 247 (6) | 31 (5) | 5 (2)# | 0.006 |
| Smoking habit | 970 (26) | 165 (27) | 106 (41)# | <0.001 |
| Alcohol abuse | 578 (15) | 83 (14) | 67 (26)# | <0.001 |
| Risk factors for aspiration other than alcohol¶ | 149 (5) | 13 (4) | 10 (6) | 0.690 |
| Prior antibiotic therapy | 900 (25) | 149 (25) | 57 (23) | 0.819 |
| Pneumococcal vaccination | 443 (16) | 58 (13) | 14 (8)# | 0.004 |
| Clinical findings | ||||
| Acute onset of disease | 1830 (48) | 334 (54)# | 125 (48) | 0.040 |
| Length of disease days | 3 (2–6)# | 4 (2–7) | 4 (2–7) | <0.001 |
| Fever | 3194 (87) | 382 (86) | 145 (77)# | 0.001 |
| Chills | 1688 (45) | 290 (47) | 110 (43) | 0.418 |
| Cough | 3080 (82) | 532 (86)# | 210 (81) | 0.022 |
| Expectoration | 2242 (59) | 398 (65) | 157 (61) | 0.052 |
| Pleuritic pain | 1474 (39)# | 367 (59)# | 201 (77)# | <0.001 |
| Signs of consolidation | 2959 (79) | 524 (85) | 200 (78)# | 0.003 |
| Confusion | 476 (13) | 69 (11) | 26 (10) | 0.314 |
| Vital signs | ||||
| Temperature °C | 38 (37.4–38.8) | 38 (37.3–38.7) | 37.7 (37–38.3)# | <0.001 |
| Pulse rate beats·min−1 | 98 (84–110) | 98 (84–110) | 107 (93–120)# | <0.001 |
| Respiratory frequency cycles·min−1 | 28 (23–32) | 28 (24–32) | 30 (24–36)# | <0.001 |
| Systolic pressure mmHg | 130 (110–145) | 129 (110–144) | 123 (109–140)+ | 0.008 |
| Diastolic pressure mmHg | 71 (63–80) | 70 (60–80) | 71 (60–80) | 0.070 |
| Oxygen saturation % | 92 (89–95) | 92 (88–95) | 92 (88–95) | 0.960 |
| Laboratory results | ||||
| C-reactive protein§ | 248 (162–359) | 260 (159–330) | 278 (187–278) | 0.992 |
| Albumin mg·dL−1 ƒ | 3.2 (2.8–3.5)# | 3 (2.8–3.4)# | 2.7 (2.2–3)# | <0.001 |
| Sodium mmol·L−1 | 137 (134–140) | 137 (134–140) | 137 (133–140) | 0.928 |
| Urea mg·dL−1 ## | 42 (31–61) | 39 (31–53) | 41 (26–64) | 0.405 |
| White cell count·mm−3×103 | 13 (9–18) | 13 (9–18) | 16 (12–22)# | <0.001 |
| Neutrophil count·mm−3×103 | 10 (6–15)# | 12 (7–16)# | 15 (10–18)# | <0.001 |
| Haematocrit % | 39 (35–43)¶¶ | 38 (35–42) | 38 (35–42) | 0.010 |
| Arterial pH | 7.46 (7.42–7.49) ¶¶ | 7.45 (7.42–7.49) | 7.45 (7.41–7.49) | 0.979 |
| Pa,O2 mmHg | 60 (53–68) | 59 (53–67) | 60 (55–68) | 0.357 |
| Pa,CO2 mmHg | 36 (32–40) | 36 (32–40) | 35 (31–39) | 0.224 |
| Positive blood cultures | 412 (12)# | 94 (16)# | 57 (23)# | <0.001 |
| PSI categories | ||||
| Class I | 369 (10) | 63 (10) | 35 (14) | 0.018 |
| Class II | 665 (17) | 82 (13)# | 49 (19) | |
| Class III | 829 (22) | 135 (22) | 62 (24) | |
| Class IV | 1365 (36) | 222 (36) | 76 (29) | |
| Class V | 584 (15) | 119 (19)# | 38 (15) | |
| CRB65 | ||||
| 0 | 997 (26) | 153 (25) | 80 (30) | 0.251 |
| 1 | 1495 (39) | 252 (41) | 108 (41) | |
| 2 | 1035 (27) | 170 (27) | 62 (24) | |
| 3 | 268 (7) | 42 (7) | 11 (4) | |
| 4 | 38 (1) | 4 (<1) | 0 | |
| Outcomes | ||||
| Mortality | 287 (8) | 52 (9) | 30 (12)# | 0.048 |
| Length of hospital stay | 7 (5–11)# | 10 (7–15)# | 17 (12–26)# | <0.001 |
Data are presented as median (25th–75th quartiles) or n (%), unless otherwise stated. UPE: uncomplicated parapneumonic effusion; E/CPE: empyema/complicated parapneumonic effusion; COPD: chronic obstructive pulmonary disease; Pa,O2: arterial oxygen tension; Pa,CO2: arterial carbon dioxide tension; PSI: pneumonia severity index. #: significantly different than the respective values in other groups by Chi-squared test with standardised residuals in categorical data or by the Kruskal–Wallis test (post hoc analysis with the Mann–Whitney test) in continuous data; ¶: n=3,418; +: significantly different than the respective values in the group without pleural effusion; §: n=160; ƒ: n=1,457; ##: n=1,116; ¶¶: significantly different than the respective values in the uncomplicated pleural effusion group.