Patient Characteristic and Microbiology Data
A total of 169578 patients visited the ED during the study period as retrieved from the hospital database. Of those, 12556 (7.40%) were suspected of infection. After exclusion, 8177 individuals met the study criteria and were categorized according to blood culture results as follows: positive bloodstream infection (741 patients; 9.06%) and negative blood culture or non-pathogen bacteremia (7436 patients; 90.94%) as shown in Figure 1. Among the variables studied, almost all were significantly different between both groups (Table 1). Merely proportion of AIDS was not significantly different between groups (2.16% in positive blood culture group and 1.44% in negative blood culture group; p 0.125). The most common Gram negative and positive pathogens were Escherichia coli (274 patients; 36.98%) and Streptococcus (76 patients; 10.26%).
Table 1. Baseline characteristics of patients with suspected infection presenting at the emergency department categorized by blood culture results.
|
ALL patients
(n = 8177)
n (%)
|
Positive blood culture
(n = 741)
n (%)
|
Negative blood culture
(n = 7436)
n (%)
|
p-value
|
Demographics
|
|
|
|
|
Age, yrs. –median (range)
|
62 (18-100)
|
62 (18-100)
|
64 (18-100)
|
<0.001
|
Male
|
4275 (52.28)
|
415 (56.01)
|
3860 (51.90)
|
0.003
|
CCI –median (range)
|
3 (0-13)
|
4 (0-13)
|
3 (0-13)
|
<0.001
|
Comorbidity
|
|
|
|
|
Age > 55 years
|
5231 (63.97)
|
537 (72.47)
|
4694 (63.13)
|
<0.001
|
Hypertension
|
2149 (26.28)
|
235 (31.71)
|
1914 (25.74)
|
<0.001
|
Solid organ malignancy
|
1878 (22.97)
|
231 (31.17)
|
1647 (22.15)
|
<0.001
|
Diabetes mellitus
|
1729 (21.14)
|
194 (26.18)
|
1535 (20.64)
|
<0.001
|
Liver disease
|
1190 (14.55)
|
191 (25.78)
|
999 (13.43)
|
<0.001
|
Moderate to severe CKD
|
639 (7.81)
|
86 (11.61)
|
553 (7.44)
|
<0.001
|
AIDS
|
123 (1.50)
|
16 (2.16)
|
107 (1.44)
|
0.125
|
History of chills
|
515 (6.30)
|
101 (13.63)
|
414 (5.57)
|
<0.001
|
Clinical presentation at triage zone
|
|
|
|
|
Respiratory rate > 22/min
|
5369 (65.66)
|
573 (77.33)
|
4796 (64.50)
|
<0.001
|
Temperature > 38.3oC
|
2658 (32.51)
|
349 (47.10)
|
2309 (31.05)
|
<0.001
|
Heart rate > 120/min
|
921 (11.26)
|
105 (14.17)
|
816 (10.97)
|
<0.001
|
Hypotension (SBP < 90 or MAP < 65 mmHg)
|
611 (7.47)
|
96 (12.96)
|
515 (6.93)
|
<0.001
|
Met Sepsis criteria
|
|
|
|
|
SIRS ≥ 2
|
6149 (75.20)
|
651 (87.85)
|
5498 (93.94)
|
<0.001
|
qSOFA ≥2
|
1230 (15.04)
|
140 (18.89)
|
1060 (14.25)
|
<0.001
|
NEWS > 7
|
2917 (35.67)
|
259 (34.95)
|
1759 (23.66)
|
<0.001
|
Lactate values
|
(n = 4694)
|
(n = 575)
|
(n = 4119)
|
|
First lactate, mmol/L-median
|
1.88
(0.01-28.33)
|
2.50
(0.01-18.71)
|
1.80
(0.01-28.33)
|
<0.001
|
First lactate > 2 mmol/L
|
2193 (46.72)
|
383 (51.69)
|
1810 (23.34)
|
<0.001
|
CKD: chronic kidney disease; SBP: systolic blood pressure; MAP: mean arterial pressure; SIRS: Systemic Inflammatory Response Syndrome; qSOFA: quick Sepsis-related Organ Failure Assessment; NEWS: National Early Warning Score.
Clinical factors and calculation of Quick Bloodstream Infection score (qBSI score)
Among three categories of studied variables, there were four significant factors in comorbid conditions, two factors at ED, and three factors beyond the 1st hour (Table 2). The six significant predictors for positive blood cultures were age over 55 years, moderate to severe CKD, solid organ tumor, liver disease, history of chills, and body temperature of over 38.3oC. The scores of each parameter were shown in Table 3 with the total score of 9. The probability of positive blood culture calculated by age over 55 years + moderate to severe CKD + solid organ tumor + (2 x liver disease) + (2 x history of fever with chills) + (2 x body temperature of over 38.3oC). If the parameter was absent or present, the values of the parameter were 0 or 1, respectively. The sum of all parameters represented probability of positive blood culture. A cutoff point of this qBSI score of 1 or over had sensitivity, specificity, PPV, NPV, LR+, and LR- of 92.98% (90.90%-94.71%), 15.40% (14.58%-16.24%), 9.87% (9.68%-10.07%), 95.66% (94.40%-96.64%), 1.10 (1.08-1.12), and 0.46 (0.35-0.60), respectively (Table 4). The ROC of qBSI score (0.66; 0.64-0.68) as shown in Figure 2.
Table 2. Factors associated with positive blood culture in patients suspected of infection presenting at the emergency department.
Factors
|
Unadjusted Odds
Ratio (95% CI)
|
*Adjusted Odds
Ratio (95% CI)
|
p-value
|
Comorbid conditions
|
|
|
|
Age > 55
|
1.54 (1.30-1.81)
|
1.33 (1.04-1.72)
|
0.02
|
Sex
|
0.84 (0.73-0.99)
|
0.94 (78.1-1.13)
|
0.52
|
Emergency severity index level
|
0.62 (0.55-0.70)
|
0.87 (0.71-1.13)
|
0.18
|
CCI
|
1.13 (1.09-1.06)
|
0.98 (0.92-1.04)
|
0.46
|
Liver disease
|
2.24 (1.87-2.67)
|
2.04 (1.59-2.61)
|
<0.01
|
Diabetes mellitus
|
1.36 (1.15-1.62)
|
1.08 (0.89-1.30)
|
0.45
|
Moderate to severe CKD
|
1.63 (1.28-2.08)
|
1.68 (1.22-2.32)
|
0.01
|
Solid organ tumor
|
1.59 (1.35-1.87)
|
1.40 (1.09-1.80)
|
0.01
|
Hypertension
|
1.34 (1.13-1.57)
|
1.14 (0.92-1.41)
|
0.24
|
On arrival parameter
|
|
|
|
History of Chills
|
2.67 (2.12-3.38)
|
1.94 (1.43-2.62)
|
<0.01
|
Temperature > 38.3°C
|
1.40 (1.32-1.50)
|
1.77 (1.39-2.25)
|
<0.01
|
Heart rate >120 /min
|
1.01 (1.00-1.01)
|
0.96 (0.73-1.26)
|
0.76
|
SBP < 90 or MAP < 65
|
2.01 (1.59-2.54)
|
1.22 (0.86-1.71)
|
0.26
|
Respiratory rate > 22/min
|
1.03 (1.02-1.04)
|
0.89 (0.71-1.26)
|
0.32
|
SIRS criteria > 2
|
2.5 (2.03-3.20)
|
1.21 (0.94-1.53)
|
0.26
|
qSOFA criteria > 2
|
1.79 (1.49-2.15)
|
1.20 (0.94-1.53)
|
0.15
|
NEWS > 7
|
1.73 (1.47-2.04)
|
0.93 (0.73-1.18)
|
0.53
|
Beyond first hour parameter
|
|
|
|
**Lactate level
|
1.13 (1.10-1.16)
|
1.10 (1.07-1.14)
|
<0.01
|
WBC > 11,000 /microliter
|
1.31 (1.12-1.52)
|
1.28 (1.03-1.59)
|
0.03
|
WBC < 3,000 /microliter
|
2.30 (1.70-3.13)
|
2.48 (1.68-3.66)
|
<0.01
|
CCI: Charlson Comorbidity Index; CKD: chronic kidney disease; SBP: systolic blood pressure; MAP: mean arterial pressure; SIRS: Systemic Inflammatory Response Syndrome; qSOFA: quick Sepsis-related Organ Failure Assessment; NEWS: National Early Warning Score; WBC: white blood cell.
*adjusted odds ratios shown in the table indicated adjusted by the studied factors shown in this table.
** lactate level is initial lactate level in mmol/L.
Table 3. Individual and adjusted odds ratio of component of the Quick Bloodstream Infection score (qBSI score) predicting positive blood culture in patients with suspected infection presenting at the emergency department.
Factors
|
Score
|
Adjusted Odds Ratio
(95% Confidence Interval)
|
p-value
|
Comorbid conditions
|
|
|
|
Age > 55
|
1
|
1.33 (1.04-1.72)
|
0.02
|
Moderate to severe CKD
|
1
|
1.68 (1.22-2.32)
|
0.01
|
Solid organ tumor
|
1
|
1.40 (1.09-1.80)
|
0.01
|
Liver disease
|
2
|
2.04 (1.59-2.61)
|
<0.01
|
On arrival parameter
|
|
|
|
History of chills
|
2
|
1.94 (1.43-2.62)
|
<0.01
|
Temperature > 38.3oC
|
2
|
1.77 (1.39-2.25)
|
<0.01
|
CKD: chronic kidney disease.
* adjusted odds ratios shown in the table indicated adjusted by the studied factors shown in the table 2.
Table 4. diagnostic properties of the Quick Bloodstream Infection score (qBSI score) predicting positive blood culture in patients with suspected infection presenting at the emergency department.
Scores
|
Sensitivity (%)
|
Specificity (%)
|
PPV (%)
|
NPV (%)
|
+LR
|
-LR
|
Score ≥ 0
|
100.00%
|
0.00%
|
9.06%
|
|
1.00
|
|
Score ≥ 1
|
92.98%
|
15.40%
|
9.87%
|
95.66%
|
1.10
|
0.46
|
Score ≥ 2
|
75.84%
|
43.69%
|
11.83%
|
94.78%
|
1.35
|
0.55
|
Score ≥ 3
|
59.65%
|
65.42%
|
14.67%
|
94.21%
|
1.73
|
0.62
|
Score ≥ 4
|
36.17%
|
84.29%
|
18.66%
|
92.98%
|
2.30
|
0.75
|
Score ≥ 5
|
21.59%
|
93.50%
|
24.88%
|
92.29%
|
3.32
|
0.84
|
Score ≥ 6
|
9.99%
|
98.00%
|
33.18%
|
91.61%
|
4.98
|
0.92
|
Score ≥ 7
|
2.29%
|
99.61%
|
36.96%
|
91.10%
|
5.88
|
0.98
|
Score ≥ 8
|
1.08%
|
99.83%
|
38.1%
|
91.00%
|
6.18
|
0.99
|
Score ≥ 9
|
0.27%
|
100.00%
|
100.0%
|
90.96%
|
|
1.00
|
Note. PPV: positive predictive value; NPV: negative predictive value; +LR: positive likelihood ratio, -LR: negative likelihood ratio