Emergence of Carbapenem resistant Gram negative and vancomycin resistant Gram positive organisms in bacteremic isolates of febrile neutropenic patients: A descriptive study
BMC Infectious Diseases
Emergence of Carbapenem resistant Gram negative and vancomycin resistant Gram positive organisms in bacteremic isolates of febrile neutropenic patients: A descriptive study
Seema Irfan 0
Faiza Idrees 0
Vikram Mehraj 0
Faizah Habib 0
Salman Adil 0
Rumina Hasan 0
0 Address: Department of Pathology & Microbiology, The Aga Khan University , Karachi , Pakistan
Background: This study was conducted to evaluate drug resistance amongst bacteremic isolates of febrile neutropenic patients with particular emphasis on emergence of carbapenem resistant Gram negative bacteria and vancomycin resistant Enterococcus species. Methods: A descriptive study was performed by reviewing the blood culture reports from febrile neutropenic patients during the two study periods i.e., 1999-00 and 2001-06. Blood cultures were performed using BACTEC 9240 automated system. Isolates were identified and antibiotic sensitivities were done using standard microbiological procedures. Results: Seven twenty six febrile neutropenic patients were admitted during the study period. A total of 5840 blood cultures were received, off these 1048 (18%) were culture positive. Amongst these, 557 (53%) grew Gram positive bacteria, 442 (42%) grew Gram negative bacteria, 43 (4%) fungi and 6 (1%) anaerobes. Sixty (5.7%) out of 1048 positive blood cultures were polymicrobial. In the Gram negative bacteria, Enterobacteriaceae was the predominant group; E. coli was the most frequently isolated organism in both study periods. Amongst non- Enterobacteriaceae group, Pseudomonas aeruginosa was the commonest organism isolated during first study period followed by Acinetobacter spp. However, during the second period Acinetobacter species was the most frequent pathogen. Enterobacteriaceae group showed higher statistically significant resistance in the second study period against ceftriaxone, quinolone and piperacillin/tazobactam, whilst no resistance observed against imipenem/meropenem. The susceptibility pattern of Acinetobacter species shifted from sensitive to highly resistant one with significant p values against ceftriaxone, quinolone, piperacillin/tazobactam and imipenem/meropenem. Amongst Gram positive bacteria, MRSA isolation rate remained static, vancomycin resistant Enterococcus species emerged in second study period while no Staphylococcus species resistant to vancomycin was noted. Conclusion: This rising trend of highly resistant organisms stresses the increasing importance of continuous surveillance system and stewardship of antibiotics as strategies in the overall management of patients with febrile neutropenia.
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Background
Febrile neutropenia is associated with high mortality rate
therefore institution of timely and appropriate empirical
antibiotic therapy is absolutely essential [1,2]. Globally
significant change in the spectrum of organisms and their
susceptibility pattern is observed in febrile neutropenic
over the past few decades. Staphylococcus aureus was the
most frequent isolate from these patients in 1950s and
early 1960s and was later replaced by Gram-negative
bacilli including Escherichia coli, Klebsiella species and
Pseudomonas aeruginosa [3]. However since 1980s,
resurgence of Gram-positive organisms in this population is
evident [4]. Recently non-fermenter Gram negative rods
such as Acinetobacter species have emerged as pathogens in
these patients [5]. Additionally use of broad spectrum
antibiotics has resulted in emergence of multi drug
resistant Gram negative and gram positive bacteria. Therefore,
the choice of empiric therapy should vary according to
locally prevalent isolates and their resistance patterns.
Currently, use of carbapenem as an empirical
monotherapy for febrile neutropenic patient is justified in most
centers due to growing resistance against other beta
lactam antibiotics [6,7]. Similarly empirical use of
vancomycin for suspected penicillin and methicillin resistant
Gram positive bacterial infection is recommended [2].
Emergence and spread of carbapenem resistant Gram
negative rods is a great concern, especially in a resource
limited country such as Pakistan, where treatment
alternatives are either unavailable or expensive/toxic with
poor outcome [8]. The Aga Khan University is a major
tertiary care hospital in Pakistan that caters a large
population of severely immuno-suppressed patients. The
hospital has a hematology-oncology unit along with a
bone marrow transplant unit. Recent reports from our
center have documented emergence and spread of
carbapenem resistance among multi-resistant non
enterobacteriaceae including Acinetobacter species and Pseudomonas
aeruginosa [9,10]. In addition, our hospital infection
control surveillance committee also reported rising trend of
carbapenem resistance in Acinetobacter species and
Pseudomonas aeruginosa, beginning from the year 2001. This
has raised the concern about possibility of emergence of
these pathogens in febrile neutropenic patients. Similarly
rising trend of methicillin resistant Staphylococcus aureus
and emergence of vancomycin resistant enterococci
amongst the hospitalized patients are of great concern
[11]. We therefore conducted a study to evaluate drug
resistance in bacteremic isolates of febrile neutropenic
patients with particular emphasis on emergence of
carbapenem resistant gram negative bacteria. In addition to
that we tried to evaluate the frequency of methicillin
resistant Staphylococcus aureus and vancomycin resistance
Enterococcus species isolated from blood cultures in these
patients.
Methods
This study was conducted in the department of Pathology
and Microbiology, Aga Khan University Karachi, Pakistan.
Medical records and blood cultures of febrile neutropenic
patients, admitted from year 1999 to 2006 were reviewed.
To evaluate the changing pattern and increasing
antimicrobial resistance of microorganisms in febrile
neutropenic patients, we divided the study duration in two
periods, the first period comprised of January 1999 to
December 2000 while the second period was from
January 2001 to December 2006.
Neutropenia was defined as neutrophil counts of 500 or
1000 with predicted decline to 500. Fever was defined as
oral temperature of 38C or above for at least one hour
[1]. Blood cultures received from all febrile neutropenic
patients between this six and half year study period were
included in the study. To avoid error the duplicates were
removed (we considered duplicate if same isolate grew
more than once during that admission).
Blood cultures were performed using BACTEC 9240
automated system. A set of aerobic and anaerobic bottles
containing brain heart infusion and thioglycolate broth
respectively, were used for cultures. Negative blood
culture bottles were incubated for seven days before being
reporting negative. Blood culture isolates were identified
using standard microbiological procedure and further
confirmation was done using commercially available API
strips [12]. Antibiotic sensitivities of all isolates except
non enterobacteriaceae were carried out using Kirby Bauer
method [13]. Sensitivity testing for non
enterobacteriaceae was done using agar dilution method as
recommended by CLSI [13].
Statistical analysis: Descriptive analysis was done by
calculating frequency and percentages. In order to evaluate
the difference in the sensitivity patterns of both gram
negative and gram positive organisms during the two halves
of the study period, chi square test or Fisher exact where
appropriate was performed with a significance level of
5%.
Results
During the study period (19992006), 726 febrile
neutropenic patients were admitted. We reviewed medical
records of randomly selected 134/726 (18.4%) patients.
Amongst these, 49% belonged to hematological
malignancy, 44% had solid organ cancer while in 7% of cases
diagnosis was not established. Chest was the commonest
site of infection (21%), followed by skin & soft tissue
(12.6%), gastroenteritis (11%), mucositis (8.2%), porta
cath (8.2%) and others (9.7%). No obvious focus of
infection was found in 25.3% cases.
A total of 5840 blood cultures were received, off these
1048 (18%) were culture positive. Amongst these, 557
(53%) grew Gram positive bacteria, 442 (42%) grew
Gram negative bacteria, 43 (4%) fungi and 6 (1%)
anaerobes. Sixty out of 1048 (5.7%) positive blood cultures
were polymicrobial. Amongst these 93.4% were positive
for two organisms, 5% for three and 1.6% for four
organisms. Increasing trend was observed in the isolation rate of
gram positive bacteria i.e. from 50% in first study period
to 54% in the second one. A little drop in isolation rate of
gram negative bacteria was noted i.e. from 43% to 41%.
No statistically significant difference for the isolation rate
of Staphylococci, Streptococci and other gram positive
bacteria was found between the two study periods, as shown in
Table 1.
Amongst the gram negative bacteria, Enterobacteriaceae
remained the predominant group, comprising of 65%
and 64% of total gram negative bacteria in the first and
second study period respectively as shown in Table 2. E.
coli was the most frequently isolated organism in both
study periods. The isolation frequency of non
enterobacteriaceae was found to be static in both study periods i.e.
2530% of the total gram negative organisms. Amongst
this group, Pseudomonas aeruginosa was the commonest
organism isolated during first study period followed by
Acinetobacter spp. However, during the second period
Acinetobacter species was the most frequent pathogen.
Another important finding was the emergence of
Stenotrophomonas maltophilia, Aeromonas species and
Achromobacter species during the second study period.
A significant rise in drug resistant isolates was noted in the
second study period. This increase was identified for all
gram negative bacteria including Enterobacteriaceae,
Pseudomonas aeruginosa, other Pseudomonas species and
Acinetobacter species as shown in Table 3a &3b. Amongst the
Gram positive Bacteremic isolates
n = 104
p-values calculated by Chi square test otherwise indicated
# p-value calculated by Fisher exact test
(Period 1) Positive blood culture
(Period II) Positive blood culture
Enterobacteriaceae, statistically significant resistance
appeared in the second study period against ceftriaxone (p
= 0.001), ciprofloxacin/ofloxacin (p = 0.003) and
piperacillin/tazobactam (p = 0.006). However no resistance
against imipenem/meropenem was detected in second
study period. Fifty four percent of Enterobacteriaceae were
ESBL positive during the second study period.
Similarly increased resistance in Pseudomonas aeruginosa
was noted against amikacin and ciprofloxacin/ofloxacin
during the second study period. However, this difference
was not statistically significant (p > 0.05). No resistance
against piperacillin/tazobactam and
imipenem/meropenem was found during the first study half; however
resistance against both of these antibiotics (6%) appeared
in the second study period. The susceptibility pattern of
Acinetobacter species shifted from sensitive to highly
resistant one with significant p values against third generation
cephalosporin (p = 0.001), quinolone (p = 0.004),
piperacillin/tazobactam (p = 0.003) and
imipenem/meropenem (p = 0.003). During the second study period 37%
(49/134) of total non- enterobacteriaceae were found
imipenem/meropenem resistant making a total of 14% (49/
352) imipenem resistance amongst all gram negative
bacteria.
Among the gram positive bacteria isolation frequency of
methicillin resistant Staphylococcus aureus was not
statistically significant (p = 0.524), however, vancomycin
resistant Enterococcus species emerged in second half of study as
shown in Table 4. No Staphylococcus species resistant to
vancomycin was isolated.
Discussion
Our study showed rising trend of carbapenem resistant
Gram negative and vancomycin resistant Gram positive
bacteria among bacteremic isolates of febrile neutropenic
n = 453
n = 352
(Period 1) Positive blood culture
(Period II) Positive blood culture
Gram Positive Bacteremic Isolates
n = 90
p-values calculated by Chi square test otherwise indicated
# p-value calculated by Fisher exact test
* p < 0.05
patients. The emergence of carbapenem resistant isolates
in our center is likely to be associated with change in
antibiotic policies. The two study periods were chosen based
on difference in empirical antibiotic choice in our center.
During nineties third generation cephalosporin was the
empirical antibiotic choice for febrile neutropenic
patients at our institute [14]. However, rising trend of
resistance against this group of antibiotics was observed
among Enterobacteriaceae and Pseudomonas aeruginosa
[15,16]. Prior to year 2000, there was limited availability
of piperacillin/tazobactam and imipenem. These agents
were introduced throughout the hospital in year 2000
[15].
Our study revealed no resistance to carbapenem and
minimal resistance against piperacillin/tazobactam in Gram
negative isolates during the first study period. However,
rising trend of resistance against these agents was noted in
second period. This change was specific for non
enterobacteriaceae group. These bacteria showed significant rise
in resistance against major antibiotics including third
generation cephalosporin, quinolone, amikacin, piperacillin/
tazobactam and carbapenem. In contrast to this no
resistance against carbapenem was noted amongst
Enterobacteriaceae group.
Another important finding was increased isolation rates
of Acinetobacter species. This organism was the sixth Gram
negative bacteria isolated during the first study period;
however it became the second most commonly isolated
gram negative bacteria during the second study period.
Moreover, carbapenem resistance in this bacterium was
significantly high (p = 0.003) during second study period,
indicating possible role of nosocomial transmission for
this rising trend. Finally, emergence of Gram negative
organism inherently resistant to carbapenem like
Stenotrophomonas maltophilia during the second study period was
another area of concern, a finding consistent with other
reports [17]. Our findings are in contrast to other regional
reports, where carbapenem resistance in this population is
not observed [18,19].
The isolation rate of MRSA during the two study halves
was comparable (p = 0.524). The isolation rate of MRSA
(31%) was significantly high when compared with the
previous study done in 1991 which reported 100%
susceptibility against cloxacillin [14]. Similar increase in
isolation rate of methicillin resistant Staphylococcus aureus
(MRSA) was also reported in another study from Taiwan
[20]. Moreover emergence of vancomycin resistant
Enterococcus species (VRE) not only poses a therapeutic
challenge for febrile neutropenic patients [21,22] but also
indirectly reflects irrational usage of vancomycin and poor
infection control practices. The increasing rates of
antimicrobial resistance amongst both Gram-positive and
Gramnegative pathogens isolated from patients with
neutropenia are posturing new therapeutic challenges. These
challenges are compounded by the fact that relatively few new
drugs are being developed, particularly those that treat
resistant Gram-negative organisms [22]. As these trends
are often associated with local treatment practices [22,23]
therefore, we suggest rational use of broad-spectrum
antibiotics especially carbapenem and vancomycin to prevent
increasing resistance against them. In addition
comproEnterobacteriaceae
Pseudomonas. aeruginosa
n = 212
n = 15
Pseudomonas species
n = 29
n = 6
n = 34
n = 52
n = 55
n = 8
p-values calculated by Chi square test otherwise indicated
# p-value calculated by Fisher exact test
* p < 0.05
n = 56
Staphylococcus species other than
aureus
Staphylococcus aureus
Enterococcus species
n = 250
p-value n = 14
n = 43
p-value n = 7
n = 23
30.2 0.735 #
13.0 0.999 #
73.9 0.290 #
mised infection control practice is another contributing
factor, hence early detection and prompt isolation of
patients with strict compliance to hand hygiene is
important to prevent further spread of multi resistant organisms.
Conclusion
This rising trend of highly resistant organisms stresses the
increasing importance of continuous surveillance system
and stewardship of antibiotics as strategies in the overall
management of patients with febrile neutropenia.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
SI conceived, planned, conducted and generated results of
the study, and drafted the manuscript. FI performed data
collection and analysis and contributed in manuscript
writing. FH and VM performed the statistical analysis and
contributed in manuscript writing. SA contributed in
provision of clinical information and approved the final
manuscript. RH participated in study design and
coordination and had contributed in manuscript writing and
final approval of script. All authors read and approved the
final manuscript.
Acknowledgements
This study was supported through a grant from the Joint Pakistan-US
Academic and Research Program HEC/MoST/USAID. We would like to thank
Dr Mohammad Khurshid, Dr Kauser Jabeen, all faculty and staff of the
Clinical Microbiology Laboratory of the Aga Khan University Hospital, Karachi
for their support and help in this study.
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