Table 1 Demographics, severity of disease, clinical, laboratory, radiological findings on admission, microbiology and empiric antibiotic therapy of the study population, according to the three study groups

n. (%)

954 (100)

771 (100)

420 (100)

Demographics

 Male, n. (%)

451 (47)

368 (48)

186 (44)

0.492

0.255

 Age, median (IQR) years

67 (47–81)

75 (61–83)

75 (61–84)

<0.001

0.868

Comorbidities, n. (%)

 Congestive heart failure

148 (16)

170 (22)

103 (25)

<0.001

0.332

 Chronic obstructive pulmonary disease

139 (15)

237 (31)

115 (27)

<0.001

0.225

 Diabetes mellitus

111 (12)

118 (15)

61 (15)

0.069

0.731

 Cerebrovascular disease

83 (9)

93 (12)

70 (17)

<0.001

0.027

 Chronic renal failure

63 (7)

63 (8)

68 (16)

<0.001

<0.001

 Liver disease

52 (6)

27 (4)

32 (8)

0.008

0.002

 Residency in a nursing home

46 (5)

63 (8)

54 (13)

<0.001

0.009

Severity on admission, n. (%)

 PSI Risk Class IV and V

332 (35)

464 (60)

343 (82)

<0.001

<0.001

 CURB-65 score 3, 4 and 5

127 (13)

198 (26)

231 (55)

<0.001

<0.001

 Admission to ICU

6 (0.6)

54 (7)

90 (21)

<0.001

<0.001

Physical findings on admission, median (IQR)

 Systolic blood pressure, mmHg

127 (112–145)

130 (115–150)

108 (85–133)

<0.001

<0.001

 Diastolic blood pressure, mmHg

70 (64–80)

71 (62–80)

60 (50–72)

<0.001

<0.001

 Heart rate, beats/minute

95 (83–107)

100 (85–114)

110 (100–120)

<0.001

<0.001

 Respiratory rate, breaths/minute

20 (18–26)

24 (20–30)

30 (24–34)

<0.001

<0.001

 SpO₂,%

96 (95–97)

92 (89–95)

90 (85–93)

<0.001

<0.001

Laboratory values, median (IQR)

 Arterial pH

7.45 (7.42-7.48)

7.44 (7.40-7.48)

7.39 (7.31-7.46)

<0.001

<0.001

 PaO₂/FiO₂ ratio

339 (318–378)

256 (216–279)

229 (182–276)

<0.001

<0.001

 PaCO₂, mmHg

33 (29–38)

36 (31–42)

36 (30–48)

<0.001

0.164

 Respiratory acidosis, n. (%)

0 (0)

59 (8)

47 (13)

<0.001

0.014

 White blood cells, cell/L⁻¹

11900 (8238–16300)

12790 (9100–17000)

144000 (9993–19000)

<0.001

0.001

 Platelet, cell/L⁻¹

232000 (182000–300500)

237000 (186500–317000)

233000 (166750–307250)

0.054

0.028

 Hemoglobin, g/dL

13 (12–14)

13 (12–14)

13 (11–14)

0.010

0.021

 Hematocrit,%

39 (36–42)

40 (37–44)

39 (34–43)

<0.001

0.001

 Urea, mg/dL

37 (27–54)

45 (31–64)

63 (42–103)

<0.001

<0.001

 Creatinine, mg/dL

0.9 (0.8-1.2)

1.0 (0.8-1.2)

1.2 (0.9-1.9)

<0.001

<0.001

 Sodium, mEq/L

137 (134–139)

137 (134–139)

136 (133–140)

0.650

0.409

 Glucose, mg/dL

105 (73–128)

113 (74–148)

101 (65–149)

0.002

0.035

Radiology findings on CXR, n. (%)

 Multilobar involvement

161 (18)

195 (28)

141 (36)

<0.001

0.003

 Pleural effusion

204 (22)

150 (20)

100 (24)

0.209

0.078

Microbiological findings, n. (%)

 Patients with isolated bacteria

184 (19)

198 (26)

141 (34)

<0.001

0.004

 Polymicrobial infection

3 (2)

8 (4)

4 (3)

0.369

0.547

 Patients with > = one MDR pathogen

17 (4)

20 (5)

22 (8)

0.015

0.060

 S. pneumoniae

90 (49)

114 (58)

64 (45)

0.064

0.027

 S. aureus

15 (8)

19 (10)

23 (16)

0.049

0.064

 Legionella pneumophila

16 (9)

16 (8)

5 (4)

0.156

0.088

 Respiratory viruses

11 (6)

12 (6)

13 (9)

0.439

0.273

 Atypicals

31 (17)

22 (11)

9 (6)

0.014

0.137

 H. influenzae

17 (9)

14 (7)

7 (5)

0.328

0.419

Empiric antibiotic therapy, n. (%)

 Levofloxacin

287 (30)

234 (30)

106 (25)

0.133

 Ceftriaxone

348 (37)

324 (42)

145 (35)

0.015

 Amoxicillin (clavulanate)

295 (31)

218 (28)

148 (35)

0.045

 Azithromycin

230 (24)

189 (25)

72 (17)

0.007

 Clarithromycin

198 (21)

211 (27)

152 (36)

<0.001

 Piperacillin/tazobactam

34 (3.6)

44 (5.7)

43 (10)

<0.001

 Antibiotics compliant with local guidelines

731 (81)

595 (79)

328 (79)

0.606

0.933

Outcomes

 Length of hospital stay, median (IQR) days

6 (3–11)

9 (6–14)

12 (7–21)

<0.001

0.004

 In-hospital mortality, n. (%)

43 (4.2)

72 (9.3)

108 (26)

<0.001

<0.001