Universitair
Ziekenhuis
ANAEROBIC BACTERAEMIA: A 10-YEAR RETROSPECTIVE
EPIDEMIOLOGICAL SURVEY
S. De Keukeleire, I. Wybo, A. Naessens, M. Van der Beken, K. Vandoorslaer, F. Echahidi, D. Piérard
Brussel
Department of Microbiology and Infection Control, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel (VUB), Laarbeeklaan 101, 1090 Brussels, Belgium
RESULTS
INTRODUCTION
•
Anaerobic bacteraemia occurs in 0.5%-12% of all positive blood
cultures, depending on geographic location, patient age and patient
demographics of the institution.
Despite its low incidence, anaerobic bacteraemia remains associated
with significant mortality, ranging from 15 to 60%.
There is evidence of an increase in anaerobic infections stated by
Blairon et al. (2006) and Lassmann et al. (2007), while others
demonstrated a decline in the incidence of anaerobic bacteraemia
(Fenner et al. (2008) – Lazarovitch et al. (2010)).
Table 1. Occurrence of all bacteraemia and anaerobic bacteraemia Evolution of proportion of anaerobic bacteraemia
Figure 2. Distribution of isolated anaerobic bacteria
Identification was verified by MALDI-TOF MS in 93.8% (410/437) and 16S rRNA gene sequencing was
performed for 27 isolates (6.2%).
A total of 152,872 blood cultures were submitted to the laboratory between 2004 and 2013. 299 patients
had anaerobic bacteraemia and 437 anaerobic organisms were isolated from their blood cultures.
During that period, the proportion of anaerobic bacteraemia compared to the number of all bacteraemia
remained stable at 5%. The mean incidence of anaerobic bacteraemia decreased from 33 cases per year
during 2004-2008 to 27 cases per year during 2009-2013 (p= 0.017) (Table 1).
Year
2004 2005 2006 2007
# all bacteraemia
620 633 608
575
# anaerobic bacteraemia
39
33
34
34
Proportion of anaerobic bacteraemia 6%
5% 6%
6%
PURPOSE
2008
574
25
4%
The overall percentage of anaerobic organisms remained stable, regarding both study periods (20042008 vs 2009-2013).
2009 2010 2011 2012 2013
553 540 561 586 541
35
23
24
30
22
6%
4%
4%
5% 4%
Figure 1. Evolution of incidence and incidence rate of anaerobic bacteraemia
The total number of annual admissions steadily increased, as well as the number of blood cultures obtained
between 2004 and 2013, while the mean incidence of anaerobic bacteraemia decreased during the study
period (1.27/1,000 admitted patients in 2004 vs. 0.94/1,000 admitted patients in 2013 (p=0.008).
The mean incidence rate of anaerobic bacteraemia also decreased from 17.3/100000 patient days (period
2004–2008) to 13.70/100,000 patient days (period 2009-2013) (p= 0.023).
In this study we conducted a retrospective study during a 10-year
period from 2003 until 2013 regarding the occurrence of anaerobic
bacteraemia.
To identify current trends a review of medical records was performed to
define clinical parameters that might be associated with the occurrence
of anaerobic bacteraemia.
2
Evolution of incidence and incidence rate of anaerobic bacteraemia,
between 2004 and 2013 at UZ Brussel
Table 2. Clinical characteristics of patients with anaerobic bacteraemia
For all 299 patients detailed clinical and outcome data were available, there was no overall statistically
significant difference in underlying patient characteristics.
The gastrointestinal tract (47%; 142/299) and wound infections (9%; 27/299) were the most frequent
sources for bacteraemia, with the origin remaining unknown in 62 cases (21%; 62/299).
25
The overall mortality rate (evaluated 7 days after the occurrence of bacteraemia) was 14% (41/299).
METHODS
15
1
10
Incidence rate
Incidence
All clinically relevant bacteraemia detected from 2004 until 2013 in the
Universitair Ziekenhuis Brussel, Belgium were included. The BacT/Alert
Microbial Detection System was used with the anaerobic (FN) bottles for
the detection of anaerobes.
20
5
The period from 2004 to 2008 was compared with 2009 to 2013.
Distributions of anaerobic organisms, clinical presentations, choices of
antimicrobial therapy and clinical outcomes were evaluated.
0
0
2004
Relevant clinical bacterial anaerobic organisms (n=437) causing
anaerobic bacteraemia were thawed and subcultured. They were grown
on fastidious anaerobic agar with 5% horse blood at 35°C for 24 to 48h
in an anaerobic chamber.
Identification was verified by matrix-assisted laser desorption ionizationtime of flight mass spectrometry (MALDI-TOF MS) using a Microflex LT
mass spectrometer with MALDI Biotyper 3.0 software and Reference
Library 3.3.2.0 or, when necessary, additional 16S rRNA gene
sequencing.
2005
2006
2007
2008
2009
2010
2011
2012
2013
No. of cases of anaerobic bacteraemia per 1,000 patients
No. of cases of anaerobic bacteraemia per 100,000 patient days
Characteristics
Male, n (%)
Female,n (%)
Age, years, mean +/- SD
Nosocomial infection, n (%)
Mortality, n (%)
ICU* stay, n (%)
Portal of entry/focus, n
Gastro intestinal
Wound infection
Gynaecological and obstetrical
Abcesses
Respiratory
Oral laesion
No focus, n
Surgery, n
Polymicrobial infection, n
Purely polymicrobial anaerobic, n
2004 - 2008 (n = 165)
96 (58)
69 (42)
64 +/- 19
80 (48)
23 (14)
31 (18)
2009 - 2013 (n=134)
72(54)
62 (46)
68 +/- 18
49 (36)
18 (13)
26 (19)
P-value**
74
19
14
7
7
4
39
42
67
98
68
10
13
8
2
3
23
34
47
87
0.52
0.19
0.89
0.62
0.11
0.50
0.13
1.00
0.47
0.38
*ICU, intensive care unit; ** Student T- test
CONCLUSIONS
A decrease in the frequency of isolation of anaerobic bacteria from blood cultures over a 10-year period is observed.
This study indicates the diagnostic role of MALDI-TOF MS, leading to rapid and accurate identification in clinical anaerobic microbiology.
Further studies focusing on the antimicrobial susceptibility and demographic background of patients are needed to objectify the currently observed trends.
The study protocol was approved by the institutional review board.
0.14
0.03
1.00
1.00