Open Access

Burns infection profile of Singapore: prevalence of multidrug-resistant Acinetobacter baumannii and the role of blood cultures

  • Christopher Tam Song1Email author,
  • Jolie Hwee2,
  • Colin Song3,
  • Bien Keem Tan2 and
  • Si Jack Chong2
Burns & Trauma20164:13

DOI: 10.1186/s41038-016-0038-8

Received: 26 September 2015

Accepted: 31 March 2016

Published: 21 April 2016

Abstract

Background

With various changes implemented such as perioperative antibiotics for tangential excision, this retrospective study reviews the infection profile of burn patients at Singapore’s only centralized burns unit. Worldwide, the appearance of multidrug-resistant (MDR) strains of Acinetobacter baumannii (A. baumannii) continues to worsen patient outcomes. This study also surveys the role of blood cultures in burns at our unit.

Methods

Four hundred fifty-two burn patients admitted to the unit between 2011 and 2013, and with cultures performed, were included in the study. The yields of various cultures were evaluated and 2684 samples were amassed, of which 984 (36.7 %) were positive. Patient variables for predictors of MDR A. baumannii infection acquisition and bacteremia were evaluated through multivariate analyses.

Results

Pseuodomonas aeruginosa (P. aeruginosa) (67 patients) was the most common organism in those with total body surface area (TBSA) burn <20 % while MDR A. baumannii (39 patients) was most prevalent in those with TBSA burn ≥20 %. We found a yield of 1.1 % positive blood cultures for TBSA burn <20 % and a yield of 18.6 % positive cultures in TBSA burn ≥20 %. The median time between surgery and bacteremia was 6.5 days (range -18 to 68 days, interquartile range 4.5); 2.9 and 8.8 % of bacteremic episodes occurred within 24 and 48 h, respectively. This is a decrease from a predeceasing study (45.3 % for 24 h and 60 % for 48 h). Multivariate analysis revealed that length of hospital stay and TBSA burn ≥20 % were predictors of MDR A. baumannii infection and positive blood cultures.

Conclusions

MDR A. baumannii infection burdens patient management, especially in those with TBSA burn ≥20 % and longer hospital stay. Prophylactic antibiotics may reduce perioperative bacteremia, but their role in MDR infections needs to be evaluated. The role of blood cultures in TBSA burn <20 % needs reconsideration.

Keywords

Drug resistant Burns Acinetobacter baumannii Blood cultures Epidemiology Singapore Infection

Background

The burns unit at Singapore General Hospital is the centralized service for the island nation and consistently reviews the infection profiles of Singapore’s burn patients. Acquiring multidrug resistant (MDR) Acinetobacter baumannii (A. baumannii) infection is associated with an increased risk of patient mortality, and outbreaks have led to the closure of wards [1]. The appearance of MDR strains of A. baumannii continues to rise and persists as a complication of burns worldwide [2]. Our unit strives to stay cognizant to the trends of culture results and antibiotics sensitivity, and this study is a comprehensive review of culture results of Singapore’s burn patients admitted between 2011 and 2013. This may be integral to the improvement of infection management in future patients.

Methods

Location

This study was conducted at the Singapore General Hospital Burns Unit, which is the sole facility for specialized burn care in the country of 5.5 million [3]. The unit consists of facilities dedicated to burn care such as an intensive care unit (ICU), a high dependency unit (HDU), an operating theater, wards, a skin lab, and a physiotherapy center.

Design of study

The inclusion criterion for the study was admission to the unit, between January 2011 and December 2013, for burn-related injuries. Of the 653 burn patients admitted during this period, 201 patients did not have cultures performed and were excluded from this study (Fig. 1). A total of 2684 cultures were collected for all 452 patients.
Fig. 1

Patient selection process according to inclusion criteria for the study

This study aims to identify patient factors, specific to Singapore’s population, that are associated with positive MDR A. baumannii cultures or positive blood cultures. Both of these may signify poorer patient outcomes. Patients were categorized according to the percentage of total body surface area (TBSA) burn.

Data collection

Data was collected from the patient records in the hospital burns database and was computed into a Microsoft Excel sheet. Data recorded included age, gender, nationality, TBSA burn, cause of burn, presence of inhalation injury intubation, length of stay, number of surgeries, and microbiology culture and sensitivity (type of culture, culture location, and multiple drug resistance status; defined as resistance to three or more antibiotics). The study attained institutional review board (IBR) approval from the Clinical Trials Resource Centre at Singapore General Hospital.

Statistical analysis

Statistical analysis was performed using SPSS version 21.0 (SPSS, Chicago, IL). Student’s t test or the Mann–Whitney U test was used for continuous variables and chi-square test or Fisher’s exact test for categorical variables. A logistic regression model was used to identify risk factors for MDR A. baumannii infections. Odds ratios and 95 % confidence intervals were calculated. We also used parameters, with a p value <0.05 following univariate analysis, to further derive the best multiple binary logistic regression model.

Results

Burn infection epidemiology

Of the 452 patients who were screened for infection, 272 (60.2 %) were found to have positive cultures (Table 1). Each patient was categorized in five groups encompassing TBSA burn of less than 10 % (I), greater or equal to 10 % but less than 20 % (II), greater or equal to 20 % but less than 40 % (III), greater or equal to 40 % (IV), and exclusively inhalational injuries (V) (Table 1). Across the groups, as TBSA burn increases, there is a trend towards an increase across all patient factors illustrated, except patient age. In general, the most common organisms cultured overall were Staphylococcus aureus (S. aureus), Pseuodomonas aeruginosa (P. aeruginosa), and MDR A. baumannii (Table 2).
Table 1

Demographics of patients included in the study

  

TBSA group

Variables

Total

I

II

III

IV

V

Patients, n (%)

452 (100)

277 (61.3)

85 (18.8)

50 (11.1)

29 (6.4)

11(2.4)

Age, year

      

 Median

40

40

42

35.5

37

48

 Range

5–94

14–94

18–83

54–82

5–70

5–70

p value

0.832

0.367

0.185

0.161

Sex

      

 Male, n (%)

255 (56.4)

151 (54.5)

43 (50.6)

35 (70.0)

23 (79.30)

3 (27.3)

p value

0.707

0.123

0.013

0.538

Nationality

      

 Foreign

176 (38.9)

84 (30.3)

41 (48.2)

31 (62.0)

18 (62.1)

2 (18.2)

p value

0.03

<0.001

<0.001

0.384

TBSA %

      

 Median

6.0

3.0

13.0

26.0

50.5

 Range

0.1–90.0

0.1–9.5

10.0–19.5

20.0–38.0

40.0–90.0

Length of stay, day

      

 Median

11

10

13

23.5

27

6

 Range

1–221

1–151

1–56

5–149

1–221

2–13

p value

<0.001

<0.001

0.013

0.582

Surgery, n (%)

365 (80.8)

222 (80.1)

73 (85.9)

45 (90.0)

25 (86.2)

0 (0)

p value

0.236

0.105

0.434

Patients with positive cultures, n (%)

272 (60.2)

172 (62.1)

35 (41.2)

36 (72.0)

25 (86.2)

4 (36.4)

p value

0.629

0.236

0.030

0.707

TBSA ​total body surface area, I TBSA burn < 10 %, II 10 % ≤ TBSA burn < 20 %, III 20 % ≤ TBSA burn < 40 %, IV TBSA burn ≥ 40 %, V Inhalational injury

Table 2

Incidence of each organism cultured in total population sample and according to TBSA group

Organism

Total infected, n (%)

I, n (%)

II, n (%)

III, n (%)

IV, n (%)

V, n (%)

Total no. of patients

452

277

85

50

29

11

Pseudomonas aeruginosa

80 (17.7)

51 (18.4)

8 (9.4)

11 (22.0)

10 (34.5)

0

Staphylococcus aureus

80 (17.7)

59 (21.3)

8 (9.4)

10 (20.0)

2 (6.9)

1 (9.1)

MDR Acinetobacter baumannii

54 (11.9)

8 (2.9)

6 (7.1)

17 (34)

22 (75.9)

1 (9.1)

MRSA

45 (10.0)

22 (7.9)

7 (8.2)

8 (16)

8 (27.6)

0

Enterobacter spp.

42 (9.3)

27 (9.7)

7 (8.2)

5 (10)

3 (10.3)

0

Acinetobacter baumannii

37 (8.2)

25 (9.0)

6 (7.1)

5 (10)

1 (3.4)

0

Klebsiella spp.

34 (7.5)

14 (5.1)

5 (5.9)

6 (12)

8 (27.6)

1 (9.1)

Enterococcus spp.

33 (7.3)

17 (6.1)

1 (1.2)

9 (18)

1 (3.4)

0

Candida spp.

30 (6.6)

10 (3.6)

1 (1.2)

8 (16)

10 (34.5)

1 (9.1)

MDR Klebsiella spp.

18 (4.0)

2 (0.7)

4 (4.7)

8 (16)

4 (13.8)

0

Proteus mirabilis

13 (2.9)

8 (2.9)

0 (0)

1 (2)

3 (10.3)

1 (9.1)

MDR Staphylococcus aureus

13 (2.9)

9 (3.2)

3 (3.5)

0 (0)

1 (3.4)

0

Escherichia coli

12 (2.7)

8 (2.9)

0 (0)

3 (6)

1 (3.4)

0

Stenotrophomonas maltophilia

11 (2.4)

5 (1.8)

1 (1.2)

1 (2)

4 (13.8)

0

MDR Pseudomonas aeruginosa

11 (2.4)

3 (1.1)

0 (0)

5 (10)

3 (10.3)

0

Group G Streptococcus

8 (1.8)

6 (2.2)

0 (0)

2 (4)

0 (0)

0

Serratia spp.

8 (1.8)

6 (2.2)

0 (0)

1 (2)

1 (3.4)

0

Morganella morganii

7 (1.5)

3 (1.1)

3 (3.5)

0 (0)

1 (3.4)

0

MDR coagulase-negative Staphylococcus

6 (1.3)

3 (1.1)

0 (0)

3 (6)

0 (0)

0

MDR Enterobacter spp.

6 (1.3)

4 (1.4)

0 (0)

1 (2)

1 (3.4)

0

Group A Streptococcus

5 (1.1)

4 (1.4)

0 (0)

1 (2)

0 (0)

0

Group B Streptococcus

5 (1.1)

5 (1.8)

0 (0)

0 (0)

0 (0)

0

MDR Escherichia coli

4 (0.9)

0 (0)

1 (1.2)

0 (0)

3 (10.3)

0

MDR Proteus mirabilis

4 (0.9)

1 (0.4)

0 (0)

2 (4)

1 (3.4)

0

Achromobacter xylosoxidans

2 (0.4)

0 (0)

0 (0)

0 (0)

2 (6.9)

0

Burkholderia cepacia

2 (0.4)

0 (0)

0 (0)

2 (4)

0 (0)

0

Staphylococcus lugdunensis

2 (0.4)

1 (0.4)

1 (1.2)

0 (0)

0 (0)

0

Trichosporon spp.

2 (0.4)

1 (0.4)

0 (0)

1 (2)

0 (0)

0

Aeromonas hydrophila

1 (0.2)

1 (0.4)

0 (0)

0 (0)

0 (0)

0

Arcanobacterium haemolyticum

1 (0.2)

1 (0.4)

0 (0)

0 (0)

0 (0)

0

Corynebacterium spp.

1 (0.2)

1 (0.4)

0 (0)

0 (0)

0 (0)

0

Clostridium spp.

1 (0.2)

0 (0)

0 (0)

0 (0)

1 (3.4)

0

Delftia acidovirans

1 (0.2)

0 (0)

0 (0)

0 (0)

1 (3.4)

0

Providencia spp.

1(0.2)

0 (0)

1 (1.2)

0 (0)

0 (0)

0

MDR Achromobacter xylosoxidans

1(0.2)

0 (0)

0 (0)

0 (0)

0 (0)

1 (9.1)

MDR Pseudomonas putida

1 (0.2)

1 (0.4)

0 (0)

0 (0)

0 (0)

0

TBSA total burn serface area, MDR multidrug-resistant, MRSA Methicillin-resistant Staphylococcus aureus

The cumulative value of the total numbers of positive and negative for each culture type and the yields are shown (Table 3). In total, 984 cultures were positive out of the 2684, giving a general yield of 36.7 %. In descending order, the cumulative yield for each type of culture were 52.6 % for wound, 52.0 % for tissue, 39.3 % for endotracheal, 27.5 % for central line, 19.5 % for urine, and 14.2 % for blood. The percentage of patients with positive cultures, out of those tested, is 19.7 % (34 out of 173). Low-yield rates include line cultures for inhalational injury (0 %), blood culture for groups I (1.6 %) and II (0 %), and urine culture for group II (0 %). The three most common organisms found in the line cultures were MDR A. baumannii (9 patients), MDR P. aeruginosa (5 patients), and Methicillin-resistant Staphylococcus aureus (MRSA) (4 patients), respectively. Endotracheal cultures revealed MDR A. baumannii (21 patients), Klebsiella (7 patients), and P. aeruginosa (4 patients) as the most common organisms in intubated patients, accordingly. The mortality rate was 2.7 % for the study cohort (12 patients).
Table 3

Yield of the various types of culture in total and according to TBSA group

  

TBSA group

Culture

Total, n (%)

I, n (%)

II, n (%)

III, n (%)

IV, n (%)

V, n (%)

Wound

323

196

64

46

17

0

 Yield

170 (52.6)

104 (53.1)

25 (39.1)

32 (69.6)

9 (52.9)

0

Tissue

1070

381

174

231

284

0

 Yield

556 (52.0)

207 (54.3)

52 (29.9)

116 (50.2)

181 (63.7)

0

Endotracheal

163

29

6

33

86

9

 Yield

64 (39.3)

8 (27.6)

2 (33.3)

15 (45.5)

36 (41.9)

3 (33.3)

Line

149

20

2

44

82

1

 Yield

41 (27.5)

5 (25.0)

1 (50.0)

13 (29.5)

22 (26.8)

0

Urine

267

83

17

75

83

9

 Yield

52 (19.5)

20 (24.1)

0 (0)

18 (24)

12 (14.5)

2 (22.2)

Blood

711

123

57

205

315

11

 Yield

101 (14.2)

2 (1.6)

0 (0)

23 (11.2)

74 (23.5)

2 (18.2)

TBSA total body surface area, I TBSA burn < 10 %, II 10 % ≤ TBSA burn < 20 %, III 20 % ≤ TBSA burn < 40 %, IV TBSA burn ≥ 40 %, V inhalational injury

MDR A. baumannii acquisition

Table 4 illustrates the antibiotic resistance profile of MDR A. baumannii isolates. MDR A. baumannii at our institution is defined as resistance to more than two classes of antibiotics. A total of 54 patients acquired MDR A. baumannii-positive cultures: 39 (72.2 %) of them presented with TBSA burn >20 % (groups III and IV). A univariate analysis of potential predictors for MDR A. baumannii was performed. Independent risk factors for MDR A. baumannii infection included length of stay, TBSA groups III and IV, intubation, and number of surgeries (Table 5). A multivariate analysis of these variables found that length of stay and TBSA groups III and IV were significant predictors of MDR A. baumannii acquisition (Table 6).
Table 4

Antibiotic resistance profile of multidrug-ressitant (MDR) Acinetobacter baumannii (A. baumannii) isolates 

No.

Isolate

No. of cultures in each profile

1

Ceft + Pip/Taz + Amp

14

2

Ceft + Cep + Cefe + Ami

10

3

Amp + Cefe + Gen

6

4

Cep + Cip + Cot

5

5

Ceft + Mero + Erta

4

6

Cip + Imi + Min

3

7

Pip/Taz + Cep + Cefe

2

8

Amp + Cep + Cip + Min

2

9

Pip/Taz + Cep + Cot + Min

2

10

Ceft + Pip/Taz + Ami + Mer + Pol

2

11

Ceft + Cip + Cot + Gen + Ert

1

12

Ceft + Pip/Taz + Amp + Cepha + Cefe + Cip + Ami + Cot + Gen + Mero + Imi + Ert

1

 

Total

54

Ceft ceftriaxone, Pip/Taz piperacillin/tazobactam, Amp ampicillin, Cep cephalothin, Cefe cefepime, Cip ciprofloxacin, Ami amikacin, Cot cotrimoxazole, Gen gentamicin, Mer meropenem, Imi imipenem, Ert ertapenem, Min minocycline, and Pol polymyxin B

Table 5

Univariate analysis of patient variables for acquisition of multidrug-ressitant (MDR) Acinetobacter baumannii (A. baumannii) infection

 

Acquired MDR A. baumannii infection

Univariate analysis

Variable

Yes (n = 54)

No (n = 398)

p value

OR

95 % CI

p value

Sex

      

 Male

36

219

0.11

Nationality

      

 Local

27

249

0.076

1.67

0.94–2.96

0.078

Age (years), mean±SD

44.3 ± 16.4

43.1 ± 17.4

0.629

Length of stay (days), mean±SD

45.8 ± 43.8

12.3 ± 8.7

<0.001

1.10

1.07–1.13

<0.001

TBSA group

      

 I

8

269

 II

6

79

0.14

2.55

0.86–7.58

0.091

 III

17

33

<0.001

17.32

6.94–43.24

<0.001

 IV

22

7

<0.001

105.68

35.05–318.60

<0.001

 V

1

10

<0.001

3.36

0.38–29.53

0.274

Intubation

26

42

<0.001

7.87

4.23–14.66

<0.001

Number of surgeries, mean±SD

3.4 ± 4.8

1.4 ± 1.9

0.03

1.23

1.11–1.35

<0.001

Prior infection

      

A. baumannii

5

32

0.79

 MRSA

9

36

0.79

P. aeruginosa

12

68

0.353

Cause of burn

      

 Scalding

8

132

0.001

0.35

0.16–0.76

0.008

 Flame

8

81

0.68

0.31–1.50

0.339

 Blast

14

40

3.13

1.57–6.25

0.001

 Others

24

145

1.40

0.79–2.48

0.255

Days to admission (days), mean±SD

2.6 ± 5.7

4.9 ± 15.8

0.032

0.963

0.91–1.02

0.196

MDR A. baumannii multidrug-ressitant Acinetobacter baumannii, OR odds ratio, CI confidence interval, TBSA total body surface area, I TBSA burn < 10 %, II 10 % ≤ TBSA burn < 20 %, III 20 % ≤ TBSA burn < 40 %, IV TBSA burn ≥ 40 %, V inhalational injury, MRSA Methicillin-resistant Staphylococcus aureus

Table 6

Multivariate analysis of patient variables for acquisition of MDR A. baumannii infection

 

Multivariate analysis

Variable

OR

95 % CI

p value

Length of stay

1.09

1.0–1.13

<0.001

TBSA group

   

 III

5.16

1.77–15.03

0.003

 IV

69.28

15.21–315.63

<0.001

Intubation

1.73

0.45–3.73

0.309

Number of surgeries

0.90

0.76–1.03

0.140

Cause of burn

   

 Blast

0.49

0.09–1.12

0.254

MDR A. baumannii  multidrug-ressitant Acinetobacter baumannii, OR odds ratio, CI confidence interval, TBSA total body surface area, III 20 % ≤ TBSA burn < 40 %, IV TBSA burn ≥ 40 %

Blood culture

Thirty-four out of 173 patients were found to have positive blood cultures (19.7 %). Two of the 34 patients presented in group I, 11 in group III, 20 in group IV, and one in group V. There was a mortality of five patients with positive blood cultures (14.7 %) and five patients with negative blood cultures (3.6 %). The most common organism identified in the blood cultures was MDR A. baumannii in 15 patients (44.1 %), followed by S. aureus in six patients (17.6 %) and P. aeruginosa in six patients (17.6 %); 30 of the patients underwent surgery, giving a median of 6.5 days (range -18 to 68 days, interquartile range 4.5–9, Q1 = 4.5, Q3 = 9) to positive blood cultures. Positive cultures 24 h after surgery was found in one patient and 48 h in another two patients.

The univariate analysis of patient demographics found that age, foreign nationality, TBSA groups III and IV, flame as a cause of burn, a MDR A. baumannii-positive culture, length of stay, and number of surgeries were significant independent risk factors for a positive blood culture (Table 7). These factors were further analyzed with multivariate logistic regression that showed length of stay and TBSA burns groups III and IV were potential predictors for positive blood cultures (Table 8).
Table 7

Univariate analysis of patient variables for positive blood culture

 

Blood culture

Univariate analysis

Variables

Positive (n = 34)

Negative (n = 139)

p value

OR

95 % CI

p value

Age (years), mean±SD

38.1 ± 15.8

46.1 ± 16.0

0.010

0.97

0.94–0.99

0.011

Sex, n

      

 Male

26

88

0.147

1.89

0.79–4.47

0.151

Nationality, n

      

 Local

13

82

0.029

0.43

0.20–0.93

0.032

 Foreigner

21

57

2.32

1.08–5.02

 

TBSA, n

      

 I

2

61

<0.001

 II

0

33

<0.001

0

0

0.998

 III

11

31

0.220

10.82

2.26–51.89

0.003

 IV

20

8

<0.001

76.25

14.94–389.10

<0.001

 V

1

6

0.720

5.08

0.40–64.63

0.210

Cause, n

      

 Flame

15

29

0.029

3.00

1.36–6.61

0.007

 Scalding

4

39

0.34

0.14–1.72

0.057

 Blast

6

28

0.85

0.32–2.25

0.743

 Others

9

43

0.80

0.35–1.87

0.611

MDR A. baumannii positive, n

18

30

0.001

4.09

1.86–8.97

<0.001

Length of stay, day

18.3 ± 16.3

53.9 ± 48.2

<0.001

1.05

1.03–1.07

<0.001

Days to admission, day

2.1 ± 4.3

2.5 ± 5.4

0.619

0.98

0.90–1.07

0.664

Days to first surgery, day

4.6 ± 6.9

5.5 ± 7.6

0.658

0.98

0.92–1.05

0.535

Number of surgeries

1.8 ± 1.8

6.2 ± 1.1

<0.001

1.44

1.22–1.70

<0.001

OR odds ratio, CI confidence interval, TBSA total body surface area, I TBSA burn < 10 %, II 10 % ≤ TBSA burn < 20 %, III 20 % ≤ TBSA burn < 40 %, IV TBSA burn ≥ 40 %, V inhalational injury, MDR A. baumannii multidrug-ressitant Acinetobacter baumannii

Table 8

Multivariate analysis of patient variables for positive blood culture

 

Multivariate analysis

Variables

OR

95 % CI

p value

Nationality

   

 Foreigner

1.82

0.47–7.15

0.388

TBSA group

   

 III

7.14

1.55–32.94

0.012

 IV

51.58

7.52–353.78

<0.001

Cause

   

 Flame

1.66

0.41–6.76

0.482

Length of stay

1.03

1.00–1.06

0.022

Number of surgeries

1.11

0.86–1.44

0.421

MDR A. baumannii-positive culture

0.79

0.15–4.29

0.786

OR odds ratio, CI confidence interval, TBSA total body surface area, III 20 % ≤ TBSA burn < 40 %, IV TBSA burn ≥ 40 % MDR A. baumannii multidrug-ressitant Acinetobacter baumannii

Discussion

Epidemiology of burn infections in Singapore so far

This retrospective analysis found that in the burns population of Singapore, S. aureus and P. aeruginosa were the most common organisms cultured. Wong et al. [4] found that with a more selective criteria of >10 % burns and a minimum 7-day hospital stay, MDR A. baumannii presented with the highest prevalence in their cohort. Similar findings in the study of burn ICU patient infections are reported [5, 6]. Table 2 may explain the cause for difference in observations, being that the most common organism cultured in group I was S. aureus while in group IV this trended towards MDR A. baumannii. Various studies [79] have demonstrated this positive correlation between longer hospital stay with increased prevalence of A. baumannii infection. Upon acute admission, stratifying patients via TBSA burns, as with this study, may allow more straightforward means of quantifying the patient’s risk of infection.

MDR A. baumannii prevalence

The care of the patients with burn wounds infected with MDR A. baumannii is challenging and carries a high mortality rate worldwide [10, 11]. Patients with prolonged hospitalization often become colonized, and the results of this study may aid anticipatory management in patients at high risk of MDR A. baumannii acquisition. Wong et al. [4] concluded that a prior MRSA infection was a risk factor to MDR A. baumannii infection. Contrary to this, the univariate analysis in Table 4 does not support the notion that A. baumannii-, MRSA-, or P. aeruginosa-positive cultures are independent risk factors for MDR A. baumannii acquisition. Wong et al. [4] also found that the number of intravascular lines placed and the Acute Physiology and Chronic Health Evaluation II score (APACHE II) on admission were significant predictive factors. The APACHE II score was not available for data collection, for the purpose of this study. However, the multivariate analysis in Table 6 supports this relationship with severe burns in ICU admissions, whereby groups III (OR, 5.16) and IV (OR, 69.28) and longer lengths of stay were significant predictors of MDR A. baumannii-positive cultures. Singapore employs a large foreign workforce that is involved in high-risk jobs that predisposes to more traumatic burn injuries. This may explain why a foreign nationality is an independent risk factor for MDR A. baumannii acquisition in Singapore.

Ward beds are implicated as reservoirs in MDR A. baumannii outbreak studies [12, 13]. In fact, an investigation used whole genome sequencing and traced an outbreak source to an operation theater and a bed [14]. The aerial dissemination of A. baumannii species presents the greatest challenge to decontaminative efforts [15]. In 2003, the unit implemented environmental and staff infection control measures including mandatory personal protective wear, hand hygiene, and terminal cleaning with hypochlorite. The beds are clear for use with three negative room samples while air is less than 60 % humidified and directed away from the patient with positive pressure airflow. A small prospective study found higher Acinetobacter- and Enterobacter-positive culture occurrences in negative pressure ventilation in the ward, while positive pressure was linked to higher prevalence of MRSA- and Streptococcus-positive cultures [16]. Barbut et al. [17] described an 88.8 % A. baumannii acquisition reduction with an infection control bundle. This included regular hydrogen perioxide vaporization disinfection, isolation of new admissions until proven negative cultures, and utilization of air purifiers. Another study [18] reported successful eradication of MDR A. baumannii after infection control interventions. The outbreak was linked to shower rooms that were found to be a colonization reservoir, and ironically, it was a common practice to shower all newly admitted patients. Their changes included improved patient showering practices, reduced use of low-concentration chlorhexidine, and cessation of occlusion dressings in third-degree burns.

The role of blood cultures in burns so far

The American Burn Association [19] defines bloodstream infection by either of two criteria:
  1. 1.

    The patient’s blood cultures must identify a recognized pathogen in two or more separate instances or in one but with signs of sepsis.

     
  2. 2.

    Patient has a common skin contaminant cultured from two or more blood cultures drawn on separate occasions (including one drawn by venipuncture) and the patient has clinical signs of sepsis.

     

Chong et al. [5] and their study of burn ICU patients found that 45.3 % of bacteremia occurred within 24 h of surgery and 60 % of episodes occurred by 48 h. Moreover, 2.9 and 8.8 % of positive blood cultures in this cohort developed within 24 and 48 h, respectively. This reduction in postoperative bacteremia may be a direct effect of the unit’s transition towards empirical antimicrobial cover during burn excision and improved aseptic techniques. Tissue cultures are sent off and antibiotics are then directed according to culture sensitivity, available 24 to 48 h later. This principle is based on the widely accepted “intraoperative bacterial shower” theory [20].

The reduced perioperative bacteremia may further emphasize better ward infection control. It remains unclear if the intraoperative empirical antimicrobials may act as a double-edged sword and encourage patient susceptibility to MDR organisms on the ward ultimately. A systematic review found no evidence that perioperative systemic antibiotic prophylaxis, compared with placebo or another antibiotic, influenced any outcome variable [21].

Blood cultures in the burn patient are expensive, invasive, and burdened with false positive results. There is a high prevalence of fever in the burn presentations that is believed to be a result of the early inflammatory response, and this may explain the high negative culture yield in the lower TBSA groups of this study (less than 2 %). The incidence of bacteremia in the higher TBSA burn may also be higher than true. An analysis of false positive results in blood cultures found an increased likelihood in severe burns [22]. It is known that skin flora alterations occur in burns and the misdirected use of antibiotics from contaminated cultures may increase patient morbidity [23].

A study found that fever peaked at 38 to 96 h after the burn injury in children, regardless of bacteremia [24]. In the hospitalized population, the literature remains divided over the use of pyrexia and a raised white cell count in the acute setting as risk factors for bacteremia [25, 26]. Keen et al.’s case-control study found that an increased threshold for blood cultures did not compromise patient outcomes and have formulated a guideline [22].

Limitations

The inclusion of all burn patients, including the burn ICU patients, creates a difficult comparison with previous burns infection studies. The study also did not include depth of burns or APACHE II scores, which were not available in the patient intranet database. The study was also not able to classify degree of bacterial invasion or acknowledge how many blood culture positives were transient since indications or antibiotic activity was not included. Lastly, the small population size of patients under group V may limit the clinical applicability of the data.

Conclusions

This large-scale retrospective study identifies key factors that predict MDR A. baumannii acquisition and positive blood cultures, especially of those with TBSA burn above 20 % and in patients with long lengths of stay. Perioperative broad-spectrum antibiotics may have reduced surgical bacteremia, but its role in acquisition of MDR infections warrants evaluation in future studies. The study also stimulates the need to scrutinize the necessity of blood cultures in patients with less than 20 % TBSA burn.

Declarations

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors’ Affiliations

(1)
University of Edinburgh
(2)
Singapore General Hospital
(3)
Cape Clinic Singapore

References

  1. Sherertz RJ, Sullivan ML. An outbreak of infections with Acinetobacter calcoaceticus in burn patients: contamination of patients’ mattresses. J Infect Dis. 1985;151(2):252–8.View ArticlePubMedGoogle Scholar
  2. Abbott I, Cerqueira GM, Bhuiyan S, Peleg AY. Carbapenem resistance in Acinetobacter baumannii: laboratory challenges, mechanistic insights and therapeutic strategies. Expert Rev Anti Infect Ther. 2013;11(4):395–409. doi:10.1586/eri.13.21.View ArticlePubMedGoogle Scholar
  3. Hofer TP, Katz SJ. Healthy behaviors among women in the United States and Ontario: the effect on use of preventive care. Am J Public Health. 1996;86(12):1755–9.View ArticlePubMedPubMed CentralGoogle Scholar
  4. Wong TH, Tan BH, Ling ML, Song C. Multi-resistant Acinetobacter baumannii on a burns unit—clinical risk factors and prognosis. Burns. 2002;28(4):349–57.View ArticlePubMedGoogle Scholar
  5. Chong SJ, Ahmed S, Tay JM, Song C, Tan TT. 5 year analysis of bacteriology culture in a tropical burns ICU. Burns. 2011;37(8):1349–53. doi:10.1016/j.burns.2011.07.020.View ArticlePubMedGoogle Scholar
  6. Chim H, Tan BH, Song C. Five-year review of infections in a burn intensive care unit: high incidence of Acinetobacter baumannii in a tropical climate. Burns. 2007;33(8):1008–14. doi:10.1016/j.burns.2007.03.003.View ArticlePubMedGoogle Scholar
  7. Altoparlak U, Erol S, Akcay MN, Celebi F, Kadanali A. The time-related changes of antimicrobial resistance patterns and predominant bacterial profiles of burn wounds and body flora of burned patients. Burns. 2004;30(7):660–4. doi:10.1016/j.burns.2004.03.005.View ArticlePubMedGoogle Scholar
  8. Öncül O, Öksüz S, Acar A, Ülkür E, Turhan V, Uygur F, et al. Nosocomial infection characteristics in a burn intensive care unit: analysis of an eleven-year active surveillance. Burns. 2014;40(5):835–41. doi:10.1016/j.burns.2013.11.003.View ArticlePubMedGoogle Scholar
  9. Manson WL, Pernot PCJ, Fidler V, Sauer EW, Klasen HJ. Colonization of burns and the duration of hospital stay of severely burned patients. J Hosp Infect. 1992;22(1):55–63. doi:10.1016/0195-6701(92)90130-E.View ArticlePubMedGoogle Scholar
  10. Trottier V, Segura PG, Namias N, King D, Pizano LR, Schulman CI. Outcomes of Acinetobacter baumannii infection in critically ill burned patients. J Burn Care Res. 28(2):248–54. doi:10.1097/BCR.0B013E318031A20F.
  11. Bang RL, Gang RK, Sanyal SC, Mokaddas E, Ebrahim MK. Burn septicaemia: an analysis of 79 patients. Burns. 1998;24(4):354–61. doi:10.1016/S0305-4179(98)00022-9.View ArticlePubMedGoogle Scholar
  12. Asai S, Umezawa K, Iwashita H, Ohshima T, Ohashi M, Sasaki M, et al. An outbreak of blaOXA-51-like- and blaOXA-66-positive Acinetobacter baumannii ST208 in the emergency intensive care unit. J Med Microbiol. 2014;63(Pt 11):1517–23. doi:10.1099/jmm.0.077503-0.View ArticlePubMedPubMed CentralGoogle Scholar
  13. Simor AE, Lee M, Vearncombe M, Jones-Paul L, Barry C, Gomez M, et al. An outbreak due to multiresistant Acinetobacter baumannii in a burn unit: risk factors for acquisition and management. Infect Control Hosp Epidemiol. 2002;23(5):261–7. doi:10.1086/502046.View ArticlePubMedGoogle Scholar
  14. Halachev MR, Chan J, Constantinidou CI, Cumley N, Bradley C, Smith-Banks M, et al. Genomic epidemiology of a protracted hospital outbreak caused by multidrug-resistant Acinetobacter baumannii in Birmingham, England. Genome Med. 2014;6(11):70. doi:10.1186/s13073-014-0070-x.View ArticlePubMedPubMed CentralGoogle Scholar
  15. Allen KD, Green HT. Hospital outbreak of multi-resistant Acinetobacter anitratus: an airborne mode of spread? J Hosp Infect. 1987;9(2):110–9.View ArticlePubMedGoogle Scholar
  16. Ahmed K, Burd A. Air conditioning in burns units. Burns. 2010;36(5):735–6. doi:10.1016/j.burns.2009.10.017.View ArticlePubMedGoogle Scholar
  17. Barbut F, Yezli S, Mimoun M, Pham J, Chaouat M, Otter JA. Reducing the spread of Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus on a burns unit through the intervention of an infection control bundle. Burns. 2013;39(3):395–403. doi:10.1016/j.burns.2012.07.007.View ArticlePubMedGoogle Scholar
  18. Lindford A, Kiuru V, Anttila V-J, Vuola J. Successful eradication of multidrug resistant Acinetobacter in the Helsinki Burn Centre. J Burn Care Res. 2014. doi:10.1097/BCR.0000000000000209.
  19. Greenhalgh DG, Saffle JR, Holmes JH, Gamelli RL, Palmieri TL, Horton JW, et al. American Burn Association consensus conference to define sepsis and infection in burns. J Burn Care Res. 28(6):776–90. doi:10.1097/BCR.0b013e3181599bc9.
  20. Elliott SD. Bacteriæmia and oral sepsis: (section of odontology). Proc R Soc Med. 1939;32(7):747–54.PubMed CentralGoogle Scholar
  21. Barajas-Nava LA, López-Alcalde J, Roqué i Figuls M, Solà I, Bonfill Cosp X. Antibiotic prophylaxis for preventing burn wound infection. Cochrane Database Syst Rev. 2013;6:CD008738. doi:10.1002/14651858.CD008738.pub2.PubMedGoogle Scholar
  22. Keen A, Knoblock L, Edelman L, Saffle J. Effective limitation of blood culture use in the burn unit. J Burn Care Rehabil. 2002;23(3):183–9.
  23. Weinstein MP, Reller LB, Murphy JR, Lichtenstein KA. The clinical significance of positive blood cultures: a comprehensive analysis of 500 episodes of bacteremia and fungemia in adults. I. Laboratory and epidemiologic observations. Rev Infect Dis. 1983;5(1):35–53.
  24. Parish RA, Novack AH, Heimbach DM, Engrav LR. Fever as a predictor of infection in burned children. J Trauma. 1987;27(1):69–71.View ArticlePubMedGoogle Scholar
  25. Bates DW, Cook EF, Goldman L, Lee TH. Predicting bacteremia in hospitalized patients. A prospectively validated model. Ann Intern Med. 1990;113(7):495–500.View ArticlePubMedGoogle Scholar
  26. Schwenzer KJ, Gist A, Durbin CG. Can bacteremia be predicted in surgical intensive care unit patients? Intensive Care Med. 1994;20(6):425–30.View ArticlePubMedGoogle Scholar

Copyright

© The Author(s) 2016

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