Association of capsular polysaccharide locus 2 with prognosis of Acinetobacter baumannii bacteraemia

Figures & data

Table 1. Comparison of the minimum inhibitory concentrations and resistance rates of capsule locus 2 (KL2) and non-capsule locus 2 (non-KL2) isolates of Acinetobacter baumannii.

	KL2 (n = 18)			Non-KL2 (n = 130)
	MIC50, MIC90 (μg/mL)	Range (μg/mL)	Resistance rate (%)	MIC50, MIC90 (μg/mL)	Range (μg/mL)	Resistance rate (%)	P^a
Amikacin	>32, >32	≤4 to >32	94.4	>32, >32	≤4 to >32	64.6	0.01
Cefepime	>16, >16	≤2 to >16	94.4	>16, >16	≤2 to >16	69.2	0.03
Colistin	1, 2	0.25 to 2	0	1, 2	0.25 to 4	0.8	0.99
Imipenem	32, 64	0.125 to >128	88.9	16, 64	0.125 to >128	56.3	0.009
Levofloxacin	>8, >8	≤1 to >8	94.4	8, >8	≤1 to >8	68.5	0.02
Minocycline	4, 8	≤2 to 16	44.4	4, 8	≤2 to 16	23.1	0.08
Sulbactam	>32, >32	≤2 to >32	94.4	16, >32	≤2 to >32	68.5	0.02
Tigecycline	4, 8	0.125 to 8	55.6	2, 4	0.125 to 8	16.8	0.001

Note: MIC₅₀, 50% minimum inhibitory concentration; MIC₉₀, 90% minimum inhibitory concentration.

^a The susceptibility to various antimicrobial agents was compared between A. baumannii capsule locus types using Fisher’s exact test.

Table 2. Demographics and clinical characteristics of patients with Acinetobacter baumannii bacteraemia.

Variable^1	KL2 (n = 18)	Non-KL2 (n = 130)	P
Demographics
Age (years)	55.4 (22.4)	64.3 (22.1)	0.07
Sex, male/female	9 (50)	71 (54.6)	0.80
Days of prior hospitalization	44.5 (30)	15 (28)	<0.001
Health-care-associated bloodstream infection	17 (94.4)	104 (80)	0.20
Underlying conditions
Charlson comorbidity index	3 (3)	3 (4)	0.78
Diabetes mellitus with end-organ damage	0 (0)	5 (3.8)	0.99
Liver cirrhosis	4 (22.2)	24 (18.5)	0.75
Cerebrovascular disease	1 (5.6)	12 (9.2)	0.99
Coronary artery disease	0 (0)	2 (1.5)	0.99
Congestive heart failure	1 (5.6)	11 (8.5)	0.99
Renal-replacement therapy	3 (16.7)	20 (15.4)	0.99
Chronic obstructive pulmonary disease	0 (0)	10 (7.7)	0.61
Autoimmune disease	2 (11.1)	3 (2.3)	0.11
Use of immunosuppressive agent(s)	6 (33.3)	44 (33.8)	0.99
Leukaemia	3 (16.7)	7 (5.4)	0.11
Lymphoma	2 (11.1)	3 (2.3)	0.11
Solid malignancy	3 (16.7)	35 (26.9)	0.57
Metastatic malignancy	2 (11.1)	21 (16.2)	0.74
Infection source
Pneumonia	13 (72.2)	46 (35.4)	0.004
Ventilator-associated pneumonia	11 (61.1)	36 (27.7)	0.007
Catheter-related infection	2 (11.1)	23 (17.7)	0.74
Primary bacteraemia	5 (27.8)	64 (49.2)	0.13
Clinical characteristic
Pitt bacteraemia score	6 (6)	4 (7)	0.18
White blood cell count (×10^3/μL)	4.8 (7.0)	8.8 (11.8)	0.03
Leucopenia (<4000/μL)	8 (44.4)	36 (27.7)	0.17
Haemoglobin (g/dL)	9.3 (2.4)	9.6 (2.7)	0.48
Anaemia (<10 g/dL)	13 (72.2)	74 (56.9)	0.31
Platelet count (×10^3/μL)	51.5 (62)	119 (148)	0.005
Thrombocytopenia (<100,000/μL)	15 (83.3)	51 (39.2)	0.001
Aspartate aminotransferase (U/L)	36 (78)	44(69)	0.44
Total bilirubin (mg/dL)	3.5 (4.5)	1.3 (3.5)	0.18
Mechanical ventilation utilization	14 (77.8)	64 (49.2)	0.03
Appropriate empirical antimicrobial therapy	9 (50)	58 (44.6)	0.80
Outcomes
All-cause in-hospital mortality	13 (72.2)	67 (51.5)	0.13
28-day mortality	13 (72.2)	55 (42.3)	0.02
14-day mortality	11 (61.1)	47 (36.2)	0.07

¹ Data are median (IQR) for continuous variables and number of patients (%) for categorical variables. The data were analysed using two-tailed Mann–Whitney U test and Fisher’s exact test, respectively.

Figure 1. Kaplan–Meier survival curves in patients with Acinetobacter baumannii bacteraemia. (A) Comparison between the capsule locus 2 (KL2) and non-capsule locus 2 (non-KL2) groups. (B) Comparison between the multilocus sequence type 2 (ST2), non-sequence type 2 (non-ST2), capsule locus 2 (KL2) and non-capsule locus 2 (non-KL2) groups at 28 days. aHR adjusted hazard ratio.

Table 3. Multivariate Cox proportional hazard model analysis of the factors predicting mortality of patients with A. baumannii bacteraemia.

	Univariate		Multivariate model 1^a		Multivariate model 2^b
Variable	Crude hazard ratio (95% CI)	P	Adjusted hazard ratio (95% CI)	P	Adjusted hazard ratio (95% CI)	P
Demographics
Age (years)	1.01 (0.99–1.03)	0.22
Sex, male	1.42 (0.87–2.31)	0.16
Days of prior hospitalization	1.01 (1.00–1.02)	0.03
Health-care-associated bloodstream infection	1.60 (0.77–3.37)	0.21
Underlying conditions
Charlson comorbidity index	1.01 (0.93–1.11)	0.77
Diabetes mellitus with end-organ damage	1.74 (0.55–5.56)	0.35
Liver cirrhosis	0.95 (0.52–1.74)	0.87
Cerebrovascular disease	1.36 (0.65–2.85)	0.41
Coronary artery disease	1.05 (0.15–7.59)	0.96
Congestive heart failure	1.61 (0.77–3.37)	0.21
Renal-replacement therapy	1.15 (0.62–2.14)	0.66
Chronic obstructive pulmonary disease	1.04 (0.42–2.59)	0.93
Autoimmune disease	2.31 (0.84–6.38)	0.11
Use of immunosuppressive agent(s)	1.03 (0.62–1.69)	0.92
Leukaemia	3.47 (1.70–7.08)	0.001
Lymphoma	1.66 (0.52–5.30)	0.39
Solid malignancy	0.54 (0.29–1.04)	0.07
Metastatic malignancy	1.21 (0.65–2.27)	0.54
Infection source
Pneumonia	1.51 (0.94–2.43)	0.09
Ventilator-associated pneumonia	1.81 (1.12–2.92)	0.02
Catheter-related infection	0.96 (0.52–1.79)	0.90
Primary bacteraemia	0.87 (0.54–1.41)	0.57
Clinical characteristics
Pitt bacteraemia score	1.33 (1.22–1.45)	<0.001	1.34 (1.23–1.46)	<0.001	1.34 (1.22–1.48)	<0.001
White blood cell count (×10^3/μL)	0.99 (0.96–1.02)	0.49
Leucopenia (<4000/μL)	2.07 (1.27–3.38)	0.004	2.16 (1.30–3.57)	0.003	2.20 (1.33–3.65)	0.002
Haemoglobin (g/dL)	0.82 (0.71–0.95)	0.009
Anaemia (<10 g/dL)	1.22 (0.75–1.98)	0.43
Platelet count (×10,000/μL)	0.92 (0.88–0.95)	<0.001
Thrombocytopenia (<100,000/μL)	3.85 (2.29–6.46)	<0.001
Aspartate aminotransferase (U/L)	1.00 (1.00–1.00)	0.25
Total bilirubin (mg/dL)	1.04 (1.00–1.07)	0.04
Mechanical ventilation utilization	2.56 (1.52–4.32)	<0.001
Appropriate empirical antimicrobial therapy	0.70 (0.43–1.13)	0.14
KL2 vs. non-KL2	2.09 (1.14–3.84)	0.02	2.03 (1.09–3.78)	0.03
Reference sequence type 2, capsule locus 2
Non-sequence type 2, non-capsule locus 2	0.31 (0.15–0.63)	0.001			0.46 (0.22–0.95)	0.04
Non-sequence type 2, capsule locus 2	0.74 (0.10–5.71)	0.77			0.49 (0.06–3.85)	0.50
Sequence type 2, non-capsule locus 2	0.67 (0.35–1.29)	0.23			0.46 (0.23–0.91)	0.03

^a Test of proportional hazards assumption: P = 0.08 > 0.05.

^b Test of proportional hazards assumption: P = 0.23 > 0.05.