Table 1 Baseline characteristics of untreated and antibiotic (AB) treated AECOPD patients during index hospitalization

Patient-related variables

Age in years, mean (SD)

70 (11)

67 (11)

71 (10)

0.003

Female sex, n (%)

158 (36.7)

58 (42.0)

100 (34.1)

0.112

BMI in kg/m², median (Q1-Q3)

24.2 (20.5–28.8)

25.3 (21.4–30.1)

23.9 (20.0–28.1)

0.007

Diabetes mellitus, n (%)

103 (23.9)

42 (30.4)

61 (20.8)

0.029

Cancer, n (%)

65 (15.1)

11 (8.0)

54 (18.4)

0.005

Heart failure, n (%)

53 (12.3)

18 (13.0)

35 (11.9)

0.746

Chronic kidney disease, n (%)

64 (14.8)

12 (8.7)

52 (17.7)

0.014

Respiratory failure (J96)

72 (16.7)

23 (16.7)

49 (16.7)

0.988

Clinical variables

Stable FEV₁% pred, median (Q1-Q3)

55 (41–68)

60 (45–73)

52 (39–66)

0.017

GOLD I (≥ 80%), n (%)

34 (7.9)

13 (9.4)

21 (7.2)

0.300

GOLD II (50–79%), n (%)

143 (33.2)

48 (34.8)

95 (32.4)

GOLD III (30–49%), n (%)

106 (24.6)

27 (19.6)

79 (27.0)

GOLD IV (< 30%), n (%)

46 (10.7)

12 (8.7)

34 (11.6)

Anthonisen criteria on admission, n (%)

 Increased dyspnea

377 (88.5)

120 (89.6)

257 (88.0)

0.644

 Increased sputum volume

130 (30.5)

24 (17.9)

106 (36.3)

 < 0.001

 Increased sputum purulence

104 (24.4)

18 (13.4)

86 (29.5)

 < 0.001

Anthonisen Type, n (%)

 < 0.001

 Type 3 (1/3)

255 (59.9)

101 (75.4)

154 (52.7)

 Type 2 (2/3) without sputum purulence

54 (12.7)

12 (9.0)

42 (14.4)

 Type 2 (2/3) with sputum purulence

43 (10.1)

8 (6.0)

35 (12.0)

 Type 1 (3/3)

54 (12.7)

7 (5.2)

47 (16.1)

Body temperature in °C, median (Q1-Q3)

36.8 (36.4–37.3)

36.6 (36.4–36.9)

36.9 (36.6–37.6)

 < 0.001

Never smoker, n (%)

8 (2.1)

2 (1.7)

6 (2.4)

0.249

Former smoker, n (%)

193 (51.3)

55 (45.5)

138 (54.1)

Current smoker, n (%)

175 (46.5)

64 (52.9)

111 (43.5)

Recent hospitalization, n (%)

51 (11.9)

10 (7.4)

41 (14.1)

0.046

Bronchiectasis, n (%)

40 (9.3)

2 (1.5)

38 (13.0)

 < 0.001

Asthma-COPD overlap, n (%)

33 (7.9)

13 (9.8)

20 (7.0)

0.325

Treatment-related variables

Maintenance inhaled corticosteroids, n (%)

270 (63.7)

76 (55.9)

194 (67.4)

0.022

Maintenance theophylline, n (%)

20 (4.7)

2 (1.5)

18 (6.3)

0.031

Azithromycin MWF, n (%)

53 (12.5)

3 (2.2)

50 (17.4)

 < 0.001

Antibiotics before admission, n (%)

117 (27.1)

31 (22.8)

86 (29.8)

0.134

In-hospital systemic corticosteroids, n (%)

362 (84.0)

121 (87.7)

241 (82.3)

0.152

Intensive care unit, n (%)

47 (10.9)

11 (8.0)

36 (12.3)

0.180

No need for ventilatory support, n (%)

93 (21.7)

35 (25.5)

58 (19.9)

0.464

Supplemental oxygen, n (%)

288 (67.1)

90 (65.7)

198 (67.8)

Non-invasive ventilation, n (%)

44 (10.3)

11 (8.0)

33 (11.3)

Invasive ventilation, n (%)

4 (0.9)

1 (0.7)

3 (1.0)

Laboratory test results

CRP in mg/L, median (Q1-Q3)

21.8 (6.5–61.9)

6.7 (2.7–16.1)

33.8 (12.5–82.4)

 < 0.001

Leucocytes in 10³/µL, median (Q1-Q3)

10.19 (7.78–13.34)

9.46 (7.53–11.78)

10.74 (7.97–14.03)

0.003

Neutrophil count in /µL, median (Q1-Q3)

6210 (4500–8880)

5680 (4192–8164)

6570 (4580–9115)

0.038

Eosinophil count in /µL, median (Q1-Q3)

110 (30–240)

145 (60–303)

100 (21–215)

0.005

pH, median (Q1-Q3)

7.417 (7.369–7.452)

7.405 (7.349–7.440)

7.421 (7.374–7.455)

0.010

PaCO₂ in mmHg, median (Q1-Q3)

40.8 (35.2–48.5)

40.4 (35.6–48.9)

41.0 (34.9–48.3)

0.790

PaO₂ in mmHg, median (Q1-Q3)

63.4 (53.1–73.1)

63.6 (53.1–71.8)

63.4 (53.0–74.2)

0.763

HCO₃⁻ in mmol/L, median (Q1-Q3)

25.4 (23.0–28.8)

25.0 (22.7–28.7)

25.8 (23.3–29.1)

0.152