The sink as a potential source of transmission of carbapenemase-producing Enterobacteriaceae in the intensive care unit
De Geyter et al. Antimicrobial Resistance and Infection Control
The sink as a potential source of transmission of carbapenemase-producing Enterobacteriaceae in the intensive care unit
Deborah De Geyter 0
Lieve Blommaert 0
Nicole Verbraeken 0
Mark Sevenois 1
Luc Huyghens 1
Helena Martini 0
Lieve Covens 0
Denis Piérard 0
Ingrid Wybo 0
0 Department of Microbiology, Vrije Universiteit Brussel (VUB), Universitair Ziekenhuis Brussel (UZ Brussel) , Laarbeeklaan 101, 1090 Brussels , Belgium
1 Department of Intensive Care Unit, Vrije Universiteit Brussel (VUB), Universitair Ziekenhuis Brussel (UZ Brussel) , Laarbeeklaan 101, 1090 Brussels , Belgium
Background: Carbapenemase-producing Enterobacteriaceae (CPE) are emerging pathogens that represent a major public health threat. In the University Hospital of Brussels, the incidence of new patients with CPE rose from 1 case in 2010 to 35 cases in 2015. Between January and August 2015, five patients became infected/colonized with CPE during their stay in the same room in the intensive care unit (ICU). Since the time period between those patients was relatively short and the strains belonged to different species with different antibiograms and mechanisms of resistance, the hypothesis was that the environment could be a possible source of transmission. Methods and results: Environmental samples suggested that a contaminated sink was the source of the outbreak. Besides other strains, Citrobacter freundii type OXA-48 was frequently isolated from patients and sinks. To investigate the phylogenetic relationschip between those strains, pulsed-field gel electrophoresis was performed. The strains isolated from patients and the sink in the implicated room were highly related and pointed to sink-to-patient transmission. In total, 7 of 8 sinks in the isolation rooms of the ICU were found to be CPE contaminated. To control the outbreak, the sinks and their plumbings were replaced by new ones with another structure, they were flushed every morning with a glucoprotamin solution and routines regarding sink practices were improved leading to discontinuation of the outbreak. Conclusions: This outbreak highlights that hospital sink drains can accumulate strains with resistance genes and become a potential source of CPE.
Carbapenemase-producing Enterobacteriaceae; Hospital sinks; Outbreak; Intensive care unit; Citrobacter freundii OXA-48; Transmission
Carbapenemase-producing Enterobacteriaceae (CPE)
represent a major public threat in both the acute and chronic
care sectors as well as in the community. Treatment of
patients infected by CPE is a challenge since only a few
drugs remain active against these strains . Between
2010 and 2014, our healthcare facility was confronted with
a rising number of CPE positive patients, with 26
confirmed cases by 2014. Patients in the intensive care
unit (ICU) comprised the majority of all colonized or
infected patients with CPE. Despite screening and
enhanced cleaning, the incidence rose further in the first half
of 2015 and could be linked to contaminated sinks.
It is described that sink drains beneath washbasins in
hospitals contain 106–1010 colony forming units (CFU)/
ml of bacteria of which approximately 103–105 CFU/ml
are Gram-negative (GN) rods, especially waterborne
bacteria . These bacteria can colonize/infect the
patient via different transmission routes. Contaminated
sinks have been implicated in several outbreaks. Kramer
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and colleagues described that sinks can be hidden
reservoirs generating large quantities of aerosols. They found
that 100% of the sinks in a neonatal ICU were
contaminated with GN rods . Starlander and co-workers
noticed that four patients became infected or colonized
by an ESBL producing Klebsiella pneumoniae strain
during a seven month period on the neurological ICU.
Environmental sampling led to the conclusion that the
plughole of the sink was the source of transmission .
The group of Lowe described an outbreak with an ESBL
producing Klebsiella oxytoca. Cultures from hand
washing sinks in the ICU unit yielded Klebsiella oxytoca with
identical molecular patterns to cultures from the
patients . Wolf and colleagues discovered that
mechanically ventilated patients were sometimes colonized with
bacteria positive for ESBLs. During a five month
observation period, four patients became colonized with ESBL
positive bacteria that were genetically identical to those
that had previously been isolated from the sink . Roux
and co-workers found that 31% of the 185 sinks in their
ICU were contaminated with ESBL positive Klebsiella
and Enterobacter species . The group of Leitner
published an article about contaminated handwashing sinks
as the source of a clonal outbreak with a resistant
Klebsiella oxytoca strain on a hematology ward .
The aim of this study was to describe an outbreak of
CPE in the ICUs of the UZ Brussels and to investigate
whether the sink could be a possible source of
transmission and in addition, whether these transmissions could
be avoided in the future by means of improving infection
control measures and replacing the sinks by new ones.
This study highlights the fact that sink drains can be
hidden reservoirs for CPE which is in general not known
by health care workers and even by infection control
The University Hospital Brussels is a teaching hospital
with more than 700 beds. There are four ICUs for
adults. Each unit contains six beds, two of them are
placed in a single room that can be closed (room one
and six; room one has an anteroom). These two separate
rooms are predominantly in use for patients who need
additional isolation precautions. Every unit has eight
sinks: one for every patient, one in the anteroom and
one placed centrally. In total there are thus 32 sinks
available in the ICUs.
New cases of patients with CPE were defined as patients
(infected or colonized) identified in the ICUs in 2015 (not
known with a CPE before 2015 or not known in another
hospital) with a CPE positive culture from any site.
Development of a colonization/infection with CPE means
that rectal screening samples were negative on admission.
An outbreak can be defined as at least two cases linked by
an epidemiological chain of transmission.
CPE surveillance and isolation policy
Patients in the ICU are screened rectally on admission;
on discharge and weekly for all patients hospitalized
more than one week. When a screening is considered as
positive, the patient is isolated on contact precautions in
a single room with use of gloves and a disposable
Environmental cleaning policy
The room has to be cleaned daily with Incidin® Plus
(0.5% glucoprotamin). At discharge, the room is cleaned
intensively and equipment such as gloves and hand
alcohol are discarded. Periodic checks of the quality of
terminal cleaning are performed with the Glowcheck®
(Hartmann, Heidenheim, Germany).
Environmental sampling and microbiological methods
Swabs (eSwab, Copan, Brescia, Italy) from the plughole
of the sink (10–15 cm depth), the environment of the
sink and room (high-touch surfaces such as the bed,
monitor, door knob, the Velcro of the blood pressure
device, matrass and curtain) were taken at several time
points. After sampling, 2 ml of Fastidious Organisms
Broth (FB, own preparation) was added to the eSwab
and incubated for 24 h on 35 °C. After one day, sink and
environmental specimens were investigated for the
presence of CPE on two separate chromogenic media:
chromID® CARBA and OXA-48 (bioMérieux, Marcy l’Etoile,
France) 48 h after sampling (24 h incubation on 35 °C).
Identification of suspicious colonies was performed by
matrix-assisted laser desorption ionization–time of flight
mass spectrometry (MALDI-TOF MS) using a Microflex
LT mass spectrometer with MALDI Biotyper 3.0 software
and Reference Library 184.108.40.206 (Bruker DaltonikGmbH,
Antibiotic susceptibility testing was performed by the
disk diffusion method and by using the interpretative
criteria of The European Committee on Antimicrobial
Susceptibility Testing (EUCAST) combined with
recommendations of the National Reference Center (NRC) and
BAPCOC (Belgian Commission for the Coordination of
the Antibiotic Policy). Colonies considered as suspicious
for the production of a carbapenemase need further
molecular characterization as a confirmation step.
Air sampling experiments
The bacterial aerosol was measured 10 cm above the sinks
during tap water running over 10 min and compared with
results without running tap water. The measurements
were performed with the MAS-100® Airsampler (Merck
Millipore, Darmstadt, Germany); programmed to measure
100 L air per minute and containing MacConkey plates
(bioMérieux, Marcy l’Etoile, France) specific for the
detection of GN bacteria. These plates were incubated for 18–
24 h on 35 °C. Samples from the environment of the sink
were also taken. Further identification and susceptibility
testing was performed as described previously (in
“Environmental sampling and microbiological methods”).
A) Bacterial colonies suspicious for the production of
Molecular characterization was performed using the
Xpert Carba-R Assay on the GeneXpert® system
(Cepheid, Sunnyvale, California, USA). Colonies
considered as suspicious for the production of
carbapenemases but with a negative result on the
GeneXpert®, were send to the NRC of CPE to
B) Genetic relatedness
To confirm genetic relatedness between isolates
from patients and environmental samples,
pulsedfield gel electrophoresis (PFGE) was performed.
Sampling in patients is part of routine daily practice.
Screening samples are taken via rectal swabs (eSwab,
Copan, Brescia, Italy). For rectal screenings and other
clinical samples, the same protocol as for environmental
sampling is followed, except that they are not enriched
Between 2010 and 2015, the number of new patients
with a CPE per year on the ICU rose from 1 to 21 and
the most abundant type became the Klebsiella
pneumoniae carbapenemase. In 2015, patients with CPE staying
on the ICU contributed 67% of all cases with CPE.
Between January and August 2015, five patients whose
Table 1 CPE carriage/infection on the ICU A, bed 6
Patient 2 (infection site: endotracheal aspirate)
Patient 4 (infection site: abdominal abscess)
Patient 5 (infection site: endotracheal aspirate)
initial screenings were negative, developed CPE carriage/
infection during their hospital stay on the ICU A in bed
6. In Table 1, the isolates from the five patients who
became positive for CPE on ICU A, room 6 are
represented. The isolates belonged to different species with
different antibiograms. The time period between the
detection of these CPE positive patients was relatively
small and since carbapenemase resistance determinants
are located on genetic mobile elements, the environment
was suspected as a possible source of transmission.
Swabs on dry surfaces taken were taken as well as swabs
from the sinks’ drain in room 6, ICU A. Two samples
became positive for CPE: the sinks’ drain and the blood
pressure cuff although a procedure for cleaning was in
place for the latter. The samples from other high-touch
surfaces were all negative for CPE, indicating that the
cleaning was appropriate.
To investigate whether other isolation rooms were also
carrying CPE in their sinks, samples were taken from
the drains. Besides one, every isolation room carried
CPE in the sink. Several species and types of CPE were
isolated: Klebsiella pneumoniae NDM, Klebsiella
pneumoniae KPC, Klebsiella pneumoniae OXA-48,
Enterobacter cloacae complex OXA-48, Citrobacter freundii
OXA-48, Citrobacter freundii OXA-48 + NDM,
Klebsiella oxytoca/Raoultella species OXA-48, and Escherichia
coli OXA-48, suggesting that resistance genes did
accumulate in the drains as patients with CPE were
preferably cared for in this rooms. The results also revealed
that in some rooms, the bacterial flora in the sink was
probably the same as the bacteria cultured in the patient.
Between the end of July and the end of August 2015, 5
patients were positive for CPE that were probably the
same as in the sinks. Three of them were not known
with a CPE on admission and here it can be stated that
the sink colonized/infected the patients. From those
three patients, two of them had positive respiratory
samples with CPE.
In 2015, Citrobacter freundii type OXA-48 was
frequently isolated from patients and sinks. To investigate the
relatedness between those strains, PGFE was performed.
KPC, OXA-48 and NDM (2/2/2015). Different species
KPC, OXA-48 and NDM (23/2/2015). Different species
OXA-48 and NDM (18/5/2015). Different species
OXA-48 (15/7/2015). Different species
NDM and OXA-48 (30/8/2015). Different species
Five patients developed CPE carriage/infection during their hospital stay on the ICU A, room six between January and August 2015. They all had negative
screenings on admission. The isolates belonged to different species with different antibiograms. The time period between the detection of these CPE positive
patients was relatively small
Citrobacter freundii CPE positive strains from patients
staying on the ICU isolated in 2013 and 2014 were also
included. These results showed that the strains isolated from
patients and sinks in room 6 are highly related (Fig. 1).
Infection control measures
In the weeks and months following the previous results,
the infection control team tried to get rid of the
outbreak by implementing new infection control measures
in addition to existing ones. Medical staff, nurses and
the cleaning personnel were informed about the
outbreak, presentations were given, the extreme
importance of correct hand hygiene was highlighted and
measurements on intensively cleaning were performed.
Since the blood pressure cuff yielded a CPE, it was
decided to work with disposable material. There was an
agreement to replace all the siphons in the isolation
rooms and to culture the siphons in the other rooms. A
daily disinfection of the sinks with Incidin® Plus
(Microtek, Zutphen, The Netherlands) was implemented. The
sinks were used for washing hands and medical
instruments before disinfection but also to flush patient’s
substances such as dialysis removals containing
antibiotics and microorganisms. These actions can promote
biofilm formation and selection of resistant bacteria.
Therefore, it was decided to use the sinks only for
“clean work”. For the removal of dialysis fluids, special
waste containers were bought.
Between September and the end of December 2015,
swabs of the plugholes of the sinks were taken on a
regular base in every room of the ICUs. Despite all the
efforts made, still 9 out of the 32 sinks (28%) were
positive for CPE at the end of September 2015. During that
time period, three patients had a sample showing CPE
but two of them were already positive on admission. A
third person had a respiratory infection with a CPE but
in his case, it was not possible to know whether this
infection was nosocomial or not since he was not screened
Because of the high number of siphons containing CPE
even after replacement, the technical department was
asked to replace all the whole sinks (not only the siphons)
by newly engineered ones with an open inlet. This makes
cleaning easier and prevents the formation of biofilms.
In general: between the 1st of January and the 31st of
December 2015, 21 patients became colonized/infected
with a CPE on the ICUs; 8 of them probably due to a
contaminated siphon. Since the replacement of the whole
sinks at the end of 2015, only one patient became positive
with a CPE in March 2016 after he had been hospitalized
on the ICU. At that moment, he was already hospitalized
for four weeks. The drain of the sink in the room where
the patient had stayed was positive with CPE, although it
was another species and strain. In this case, it was hard to
say whether the CPE was transmitted from the sink to the
patient or the other direction since the patient was not
Fig. 1 Phylogenetic relatedness between Citrobacter freundii CPE strains. On the left side of the figure, a dendogram is shown representing the
relationship between the strains in %. In blue, the patients’ and drain cultures from ICU A bed 6 are shown and in black, the patients’ and drain
cultures from ICU A bed 1are represented together with the date of isolation. The strains isolated from patients and sinks in room 6 are highly related
screened on admission. The other sinks stayed negative
until the last day of the sampling and no other
transmissions were noted.
Airsampling experiments with two sinks showed that
it is possible that bacteria in the biofilm of the sink can
get carried up into the air above the drain through
aerosols when tap water is running, since we were able to
pick up Gram-negative bacteria in the air and the
environment on the sink after tap water was running. In the
air, Stenotrophomonas maltophilia, Serratia marcescens,
Pseudomonas oleovorans group and Pseudomonas putida
were recovered. On the taps, Serratia marcescens and
Pseudomonas fluorescens group were found and on the
rims, Serratia marcesens CPE suspected and
Stenotrophomas maltophila were cultured.
The prevalence of infections with multidrug resistant
(MDR) GN bacteria such as CPE is increasing worldwide
 and there is probably a wider range of environmental
reservoirs for those bacteria compared with Gram
positive MDR bacteria .
Both the results in the literature and in this work show
that the sink is an ideal moist reservoir for (waterborne)
GN bacteria to survive. The fact that fluids, often
containing antibiotics, were flushed through the drains,
promotes the selection of resistant bacterial strains. Despite
the efforts made and the discontinuation of the outbreak
with CPE on ICU A room six, even after replacing the
complete sinks, we could find multiresistant Pseudomonas
species and Stenotrophomonas maltophilia. Both bacteria
can also colonize/infect patients and indeed, we noticed
that some patients showed positive respiratory samples
with those species after a few days of hospitalization on the
ICU (data not shown). However, we didn’t do molecular
characterization to prove this hypothesis.
Air sampling experiments taught us that the air above
and the environment of the sink got contaminated with
bacteria after tap water was running. Hands of health
care workers can be contaminated via this way. This
underlines the primordial importance of hand hygiene. A
limitation of the study is that although we could pick-up
bacteria in the air and the environment of the sink after
water was running, we could not prove that these
bacteria really came from the biofilm of the siphon and we
were not able to pick up CPE in the air above the sink.
This is possibly due to the limited time and availability
of the siphons for the measurements in order to not
disturb the critical ill patients in the room.
In the next years, a new ICU will be built in the UZ
Brussels. A few propositions according to the
architecture of the room and sinks can be made. First of all, it
was considered not to place sinks in the rooms. Sinks
were used to wash reusable medical devices before
disinfection, as waste bins and as water suppliers for
shaving men. Reprocessing of reusable medical devices
should be centralized, shaving can be done by means of
a separate wash basin and fluids have to be removed in
special containers that provide easy transport to the
utility room. Body fluids should not be flushed through the
sink anymore. A second possibility is to build a room
with two separate sinks. One sink should be rigorously
restricted to hand washing. The sinks used for waste
disposal should be systematically considered as potentially
contaminated. In our ICUs, the distance between the
sink and the patient’s bed is less than one meter. There
are no guidelines about the minimum distance required
and it depends also on the sink’s architecture, but as
seen in literature, aerosols and splashes coming from the
plughole of the sink can be propagated up to 1 m from
the sink when the tap is turned on . Therefore, we
suggest that the distance between a sink and a patient’s
bed should be at least two meter.
In our ICU, there are two types of taps. The taps in
the isolation rooms are designed well with a distance
between tap and inlet of 40 cm. In contrast, the taps in
the standard rooms are not ergonomically designed: the
distance between the tap and the inlet of the wash basin
is too small (20 cm) which makes it possible to
contaminate the tap when water is running. In the future, we
will replace them. Moreover, in the sinks of the standard
rooms, water from the tap is directed straight into the
outlet, allowing splash-back from the sink’s drain trap.
A German company brought a self-disinfecting siphon
on the market (MoveoSiphon ST24, MoveoMed, Dresden,
Germany). That device prevents the formation of a biofilm
in the sink by means of permanent physical disinfection,
electromagnetic cleaning and antibacterial coating .
This siphon was tested during five months (July- November
2016) in the ICU A room 1 for the presence of GN bacteria.
During that entire period, we could not pick up any GN
bacteria (data not published). However; there still need to
be investigated whether that siphon could really prevent
nosocomial transmissions in our ICUs and whether this
intervention will be cost-effective.
There can be concluded that the environment is an
important reservoir for MDR Gram-negative bacteria, as
demonstrated in this CPE outbreak linked to
contaminated sinks. Despite the efforts already made and the
discontinuation of the outbreak in ICU A, some sinks are
to date still contaminated with MDR strains. Therefore,
different disciplines need to sit together and decide about
how to change our “sink attitude” and how to make
structural changes to the architecture of a patient’s room in a
way that it stays both practical for the health care workers
BAPCOC: Belgian commission for the coordination of the antibiotic policy;
CFU: Colony forming units; CPE: Carbapenemase-producing
Enterobacteriaceae; ESBLs: Extended-spectrum β-lactamases; EUCAST: The
European committee on antimicrobial susceptibility testing; FB: Fastidious
organisms Broth; GN: Gram-negative; ICU(s): Intensive care unit(s); MALDI-TOF
MS: Matrix assisted laser desorption/ionization-time of flight mass
spectrometry; MBL: Metallo-β-lactamase; MDR: Multidrug resistant; NDM: New
Delhi metallo-β-lactamase; NRC: National reference center; OXA: Oxacillinase;
PFGE: Pulsed-field gel electrophoresis
DDG was the writer of this article and the main investigator of this work. LB,
NC and IW helped to set up the infection control measures and the study
design. IW and DP corrected the draft of the manuscript. MS and LG helped
in the follow-up of the infection control measures in the ICU. HM performed
the PFGE. LC conducted the identification and susceptibility testing of the
strains. All authors read and approved the final manuscript.
Ethics approval and consent to participate
This study was approved by the Ethical Medical Committee of the UZ
Brussels (number B.U.N. 143201526301).
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