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Journal of Clinical Microbiology, March 2002, p. 799-804, Vol. 40, No. 3
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.3.799-804.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Extended-Spectrum ß-Lactamase-Producing Klebsiella pneumoniae in a Neonatal Intensive Care Unit in the High-Prevalence Area of Athens, Greece
E. Lebessi,1 H. Dellagrammaticas,2 P. T. Tassios,3 L. S. Tzouvelekis,3 S. Ioannidou,1 M. Foustoukou,1 and N. J. Legakis3*
Department of Microbiology,1
Neonatal Intensive Care Unit, P. & A. Kyriakou Children's Hospital,2
Department of Microbiology, Medical School, University of Athens, Athens, Greece3
Received 30 July 2001/
Returned for modification 22 September 2001/
Accepted 12 December 2001

ABSTRACT
Extended-spectrum ß-lactamase-producing
Klebsiella pneumoniae (EPKP) strains are frequently implicated in outbreaks
in neonatal intensive care units (NICUs). During the period
from 1997 to 1998, 21 infections and 23 colonizations with EPKP
were recorded in the NICU of a children's hospital in Athens,
Greece. Seventeen of the infected and 12 of the colonized neonates
had been referred from other hospitals. The remaining infections
and colonizations occurred during the current hospitalization.
Pulsed-field gel electrophoresis typing showed that the latter
cases were due to an outbreak strain that persisted in the unit,
while the repeated introduction of EPKP carriers was mostly
due to clonal outbreaks in two maternity hospitals.

INTRODUCTION
Klebsiella pneumoniae has been recognized as an important cause
of infections in hospitalized neonates (
8). Various environmental
reservoirs have occasionally been identified in outbreaks caused
by
K.
pneumoniae in such settings (
6,
11). Irrespective of the
primary source, it seems that the most significant reservoir
of the microorganism is the digestive tract of colonized patients
and that transmission occurs mostly via the hands of nursing
staff (
3,
8). During the past decade, strains of
K.
pneumoniae exhibiting resistance to newer cephalosporins due to the production
of extended-spectrum ß-lactamases (ESBLs) have been
frequently implicated in outbreaks in pediatric hospitals and
neonatal intensive care units (NICUs) (
1,
15,
16,
20). These
strains usually exhibit cross-resistance to other antibiotics,
such as aminoglycosides. Therapeutic options are therefore limited.
Up to 1996, broad-spectrum cephalosporin-resistant K. pneumoniae strains (i.e., putative ESBL producers) were rarely isolated in one of the major children's hospitals in Athens, Greece. However, during 1998, a relatively high rate of isolation of ESBL-producing K. pneumoniae (EPKP) strains in the NICU was observed. With the aid of molecular typing, we showed in the present study that most EPKP acquired during hospitalization originated from a single strain. We also found that the majority of EPKP isolated on admission belonged to a limited number of strains that were endemic in referring maternity hospitals.

MATERIALS AND METHODS
Setting.
P. & A. Kyriakou Children's Hospital is one of the two major
pediatric hospitals in Greece. It is a 358-bed tertiary-care
institution with an average yearly admission of 22,000 patients.
In the NICU, with about 700 admissions per year, there are 30
incubators, 11 of which provide intensive care facilities. As
there is no attached maternity unit, all babies admitted to
the NICU are referred for tertiary care from the greater Athens
region, parts of southern Greece, and many of the islands.
Isolation of EPKP.
EPKP strains were isolated from clinical material submitted to the hospital microbiology laboratory or from body surface cultures (rectal and umbilical swab and nasopharyngeal secretion samples) used to screen colonized patients on admission to the hospital. The latter cultures were done with McConkey agar containing ceftazidime (1 µg/ml) to facilitate isolation of EPKP. All cases of colonization or infection were classified as referred to or acquired in the hospital. Referred cases were those from which an EPKP strain was isolated from surface cultures upon admission or within 48 h after admission. Attempts to isolate EPKP strains from the environment were also made. Environmental screening was performed by using swabs moistened with sterile saline and included work surfaces, sinks, incubators, solutions, and equipment used in intubation. Hand impressions were also taken in order to examine carriage of EPKP by the medical and nursing staff of the NICU. Samples were cultured on ceftazidime-containing medium as described above. Microorganisms were identified with the API 20E system (bioMerieux, Marcy l'Etoile, France).
Susceptibility testing and ESBL detection.
Susceptibility to antimicrobial drugs was tested by a disk diffusion method with Mueller-Hinton agar (14). Production of ESBLs was detected by the double-disk synergy test (DDST) (9) with disks of amoxicillin-clavulanic acid surrounded at a radius of 30 mm by cefotaxime, ceftazidime, aztreonam, and cefepime. This test was integrated in the routine susceptibility testing. When necessary, ESBL production was confirmed by using ESBL-detecting Etest strips containing ceftazidime and clavulanic acid (AB Biodisk, Solna, Sweden). MICs of various antibiotics, including ceftazidime and cefotaxime, were determined by using the Etest (AB Biodisk).
Typing.
Molecular typing was carried out by pulsed-field gel electrophoresis (PFGE). Genomic DNA was prepared as described previously (17). After XbaI digestion, the DNA was electrophoresed through 1% agarose-0.5x Tris-borate-EDTA in a CHEF-DRIII apparatus (Bio-Rad Laboratories, Hercules, Calif.) under the following conditions: 14°C and 120° switch angle for 20 h with a linear switch time ramp of 5 to 55 s. Digitized gel images were processed by using the GelCompar software package (Applied Maths, Kortrijk, Belgium). Banding pattern similarities were estimated by using the Dice coefficcient. A 2% tolerance in band position differences was allowed. Matrices of similarity coefficients were clustered and a dendrogram was constructed by the unweighted pair-group method with arithmetic averages.

RESULTS
The first case of infection due to an EPKP strain was recognized
in May 1997 (isolate 1221; Table
1). This neonate had been admitted
to the NICU from the maternity unit of a general hospital (GH-I)
due to sepsis caused by an EPKP. The next two patients infected
by EPKP (isolates 1253 and 1517; Table
1) were referred from
a maternity hospital (MH-II) in September 1997. Additionally,
three sporadic cases of infection by EPKP (one in May 1997 and
two in July 1997) occurred in other wards of P. & A. Kyriakou
Children's Hospital. After these incidents, an attempt was made
to strengthen the general hygienic measures (better adherence
to hand-washing practices and more frequent changes of gloves)
and to isolate or group EPKP-colonized patients. Also, the DDST
was routinely applied for all enterobacterial isolates. Especially
for the NICU, it was decided to examine the admitted neonates
by body surface cultures for EPKP carriage and to perform periodically
environmental and 1-day surveys. Examination for EPKP colonization
started in November 1997 and ceased at the end of 1998.
From May 1997 to December 1998, 799 neonates were admitted to
the NICU. Infection due to EPKP was documented in 19 patients;
in 2 more patients, EPKP (isolates 1509 and 1561) was considered
a potential cause of infection (Table
1). Fourteen of these
21 neonates had been referred from two maternity hospitals in
Athens, MH-I (
n = 10) and MH-II (
n = 4). Three patients were
referred from maternity units of general hospitals (GH-I, GH-II,
and GH-III) also located in the Athens area. The remaining four
strains were most likely acquired during hospitalization in
the NICU, a conclusion corroborated by the fact that body surface
cultures upon admission were negative for EPKP. An EPKP was
likely to be responsible for urinary tract infection in 12 neonates,
for bacteremia or sepsis in 6 neonates, and for respiratory
tract infection in 3 neonates. Empirical treatment was initiated
with ampicillin plus gentamicin. Upon confirmation that the
strain was an ESBL producer, the therapy was switched to imipenem
and/or an aminoglycoside, depending on the susceptibility profile
and the type of infection.
From November 1997 to December 1998, it was feasible to examine by body surface cultures on admission 390 of 567 neonates. The remaining patients were not examined due to limited staff during nighttime and weekends. Twelve neonates were found colonized with EPKP (Table 2). Eight of them had been referred from MH-I, and three had been referred from MH-II. One patient was referred from a general hospital (GH-IV) outside Athens. Additionally, 11 colonized patients who most likely acquired EPKP during their stay in the NICU were detected in the four 1-day surveys conducted in 1998 (9 January, three isolates; 20 February, three isolates; 25 July, two isolates; and 10 September, three isolates). In nine patients, the initial surface cultures were negative for EPKP. The remaining two patients were not examined upon admission. Nineteen of the 23 isolates obtained from colonizations were found either in feces only or in feces and nasopharyngeal secretions.
The two environmental surveys conducted in 1998 (20 February
and 25 July) as well as examination of the hands of NICU personnel
were carried out in parallel with the respective 1-day surveys
mentioned above. The first environmental survey yielded no EPKP,
while an EPKP isolate was obtained from a weighing scale in
the NICU during the second environmental survey (isolate 1459;
Fig.
1). No EPKP isolates were recovered from the hands of NICU
personnel.
Forty-four isolates were available for typing by PFGE. Sixteen
and 12 isolates were from infections (Table
1) and colonizations
(Table
2), respectively. The EPKP environmental isolate as well
as 11 EPKP clinical isolates found in other hospital wards during
the study period were also typed by PFGE. Four additional epidemiologically
unrelated EPKP strains were included for control purposes. PFGE
revealed five clusters (A to E) of isolates with identical or
highly similar (>80%) PFGE fingerprints (Fig.
1 and
2).
Eleven of 13 tested isolates derived from infections or colonizations
that had occurred during hospitalization in the NICU belonged
to PFGE cluster A (95% similarity of band patterns). The EPKP
isolate obtained from the surface of a weighing scale during
the second environmental screening also belonged to this cluster.
Isolation dates spanned a period of 8 months (from February
to September 1998). Notably, isolates of cluster A appeared
susceptible to broad-spectrum cephalosporins upon standard susceptibility
testing (MICs for ceftazidime and cefotaxime ranged from 4 to
8 and from 2 to 8 µg/ml, respectively). Nevertheless,
they were positive in the DDST. The results of confirmatory
testing by using ESBL-detecting Etest strips were also positive.
These isolates were resistant to all tested aminoglycosides
(gentamicin, netilmicin, tobramycin, and amikacin).
EPKP isolates 1352 and 1315 (Tables 1 and 2, respectively), which were also acquired during hospitalization in the NICU, were indistinguishable (97% similarity), composing PFGE cluster B (Fig. 1 and 2). Both were resistant to ceftazidime and cefotaxime (MICs, >32 µg/ml) as well as to all four aminoglycosides tested.
Six isolates imported from MH-II, spanning isolation dates from December 1997 to August 1998, were grouped together in PFGE cluster C (86% similarity) (Fig. 1 and 2). This cluster also included one nosocomial isolate obtained from a medical ward (isolate 1535; Fig. 1) in September 1998. It can therefore be considered to represent an EPKP clone endemic in MH-II but which nevertheless spread to another ward of P. & A. Kyriakou Children's Hospital. All six cluster C isolates were resistant to ceftazidime and cefotaxime (MICs, >32 µg/ml). They were also resistant to netilmicin, tobramycin, and amikacin but susceptible to gentamicin.
Similarly, PFGE cluster D consisted of highly related isolates (94%), all of which were imported from MH-I and could therefore be considered representative of a clone endemic in that hospital. Cluster D included 10 isolates that were obtained throughout 1998 and that exhibited a multidrug resistance phenotype similar to that of cluster C isolates.
Cluster E was composed of three nosocomially acquired isolates with indistinguishable PFGE patterns (100% similarity). They were obtained from children hospitalized in the oncology ward and the internal medicine ward between April and September 1998. Their resistance pattern was similar to that of cluster B isolates. The remaining seven EPKP isolates derived from wards other than the NICU during the study period exhibited unique PFGE types (Fig. 1).
Isolates of all clusters were susceptible to cefepime, imipenem, and the combination of piperacillin and tazobactam. However, susceptibilities to amoxicillin-clavulanate varied, even within clusters. All isolates were also susceptible to ciprofloxacin.

DISCUSSION
Infections due to multiantibiotic-resistant
K.
pneumoniae are
frequent in Greek hospitals (
7,
12,
13,
18,
19). Control of
epidemics due to this pathogen may benefit from detailed typing.
As also demonstrated here, PFGE is effective in delineating
the epidemiology of
K.
pneumoniae nosocomial infections (
6,
15). The results provided by PFGE showed that a distinct "in-house"
strain (cluster A) was responsible for most colonizations and
infections that occurred during hospitalization. It is not inconceivable
that this
K.
pneumoniae strain had been established in the NICU
earlier than 1997, since it would be easily overlooked due to
its apparent susceptibility to the broad-spectrum cephalosporins.
This "discrepancy" is encountered more frequently in SHV-type
ESBL producers (
2). Thus, the application of DDST was helpful
in identifying and tracing this endemic clone. The usefulness
of synergy tests in detecting ESBL producers with low-level
resistance to newer cephalosporins was also emphasized in a
previous study (
4). The origin of this resident strain and its
mode of spread in the NICU were not elucidated. Isolation from
the surface of a weighing scale indicated that occasional environmental
contamination might also have contributed to its persistence
in the NICU. Notwithstanding its presence in the NICU for at
least 1 year, this strain had not spread to other wards. Conversely,
a strain of PFGE type E that did persist for at least 5 months
in other wards of the hospital was never isolated in the NICU.
A notable finding was the repeated isolation of EPKP from neonates upon admission from two large maternity hospitals in Athens (MH-I and MH-II). Molecular typing provided evidence that this finding was due to ongoing clonal outbreaks that presumably had been going unnoticed. Extensive dissemination of the EPKP clones was also indicated by the fact that approximately 2% of the neonates admitted from MH-I and MH-II were colonized by EPKP. Both implicated maternity hospitals were notified of the problem. Action on their part may well have contributed to the drastic reduction in the numbers of EPKP-infected or -colonized neonates admitted to the NICU from December 1998 to February 1999. Screening of patients upon admission also ceased at the same time; therefore, the reduction of the extent of colonization cannot be estimated. While we were aware of the low value of body surface cultures in predicting microorganisms causing severe infections in neonates (5, 10), this approach enabled us to identify EPKP carriers in a timely fashion. The control measures taken, including either isolation or grouping of these patients, may have been responsible, at least in part, for the fact that none of the imported strains was established in the NICU. Unexpectedly, the strain endemic in MH-II did appear in a single patient in the general pediatric ward. The origin of this phenomenon could not be ascertained.
The high prevalence of EPKP in Athens tertiary-care hospitals was documented in previous studies (12, 13). Measures implemented since 1991 have been aimed at the reduction of cephalosporin usage and the strengthening of infection control, primarily in intensive care units, considered the main foci of ESBL-producing enterobacteria (21). So far, a systematic evaluation of the effectiveness of these measures has not been undertaken. However, the spread and persistence of EPKP in major pediatric and maternity hospitals as well as in maternity units of general hospitals around Athens indicate that the policy followed has largely failed and must be revised.

FOOTNOTES
* Corresponding author. Mailing address: Department of Microbiology, Medical School, University of Athens, Asias 75, Athens 11527, Greece. Phone: 30-1-7462011. Fax: 30-1-7462124. E-mail:
nlegakis{at}med.uoa.gr.


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Journal of Clinical Microbiology, March 2002, p. 799-804, Vol. 40, No. 3
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.3.799-804.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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