1. antibiotics go unrecognised. He added
that as many as 40 per cent of Pseudomonas
infections in intensive care units may
be acquired from water systems.
So how does the organism
get into water? Like
Legionella, Pseudomonas
can enter in small
numbers in mains waters
and then form biofilm
in conducive conditions,
such as stagnant water
in system dead legs.
‘Retrograde’ contamination,
where the organism is
transmitted back to a tap from an
infected individual, has been also been well-
documented. This may be caused when sinks
are used for inappropriate disposal of patient
secretions and are poorly cleaned, which
transfers the organism to the outlet.
Eighty to 90 per cent of Pseudomonas
contamination occurs in the periphery of water
systems, which can be harder to eradicate than
contamination of main systems. Pseudomonas
also favours limescale deposits and trapped
debris in flow straighteners and aerators in tap
Environmental Health News • May 2013 • 29
Resources
A missed epidemic
Water
samples can
only ever
provide a
snapshot
in time
I
t was only in January last year that
Pseudomonas — specifically P. aeruginosa
— was flagged up in earnest as being
transmitted by water. Three babies
in a Belfast neonatal unit died from
infections traced back to contaminated
taps and the resulting media attention led to
pressure on regulatory bodies to work out
what lessons needed to be learned.
Superseding the Department of Health’s
interim advice following the Belfast
incident, new guidance has been issued on
controlling and minimising the risks from
P. aeruginosa associated with water outlets.
The document is an addendum to Health
Technical Memorandum 04-01 on the control
of Legionella in water systems. It addresses
how to assess risk, water sampling, testing
and monitoring, remedial actions, and
development of water safety plans.
Although aimed mainly at augmented care
units, the addendum’s recommendations
also have implications for health
and safety in care facilities,
where there may be residents
with compromised immune
systems. This might be as a
result of treatments such
as chemotherapy or due to
other pre-disposing factors
for Pseudomonas infection,
such as chronic wounds or
points of entry for catheters or
ventilation tubes.
Like Legionella bacteria,
P. aeruginosa bacteria inhabit moist
environments because they can form a
‘biofilm’ that attaches to inanimate surfaces.
While the organism is only problematic for
those with weakened immune systems, the
dangers to those affected are constantly
increasing as the organism has become highly
resistant to many antibiotics.
At a meeting sponsored by Pall Medical,
Dr Mike Weinbren, director of infection
prevention and control at University Hospitals
Coventry and Warwickshire, said Pseudomonas
infections associated with water are not
new: there are reports of outbreaks from
before 2000.
Dr Weinbren said that there may be a
‘missed epidemic’: the literature is dominated
by infections caused by resistant strains,
so many other instances of waterborne
Pseudomonas infections that are sensitive to
outlets. Both Pseudomonas and Legionella have
been found inside the complex mechanisms
of infra-red operated taps. Thermostatic mixer
valves and EPDM (synthetic rubber) hoses,
which use materials susceptible to biofilm
formation, can also be problematic.
Also speaking at the meeting,
microbiology consultant and former
directorate manager of the Department of
Medical Microbiology at Royal Liverpool
and Broadgreen University Hospitals
Dr Tom Makin noted that many of the
control mechanisms for Pseudomonas are
similar to those for Legionella.
A
voidance of build-up of
biofilm is crucial, he said,
with regular flushing of
outlets the key to preventing
stagnation. He also stressed
that: ‘You cannot be
certain that outlets are completely clear of
Pseudomonas and Legionella just by doing risk
assessments and testing. Water samples can
only ever provide a snapshot in time. This is
because sampling will only pick up free-floating
forms, so sampling must take place when the
outlet has been least used.’
Other control measures include avoidance
of aerators, flow straighteners, overly-complex
infra red outlets, TMVs and flexible hoses.
Patient secretions should not be put down
sinks, Dr Makin said, and cleaning staff should
be trained on the correct cleaning procedures
for taps and sinks.
In most situations the only way of being
absolutely sure that water is free of bacteria
is to install point-of-use (POU) filtration
incorporating 0.2μm membranes. This
is confirmed in the new guidance, which
recommends POU filters on outlets as an
option in this context and as a possible solution
in the event of contamination. E
The Dublin Masterclass, chaired by
Hilary Humphreys, professor of clinical
microbiology and consultant microbiologist
at Beaumont Hospital, Dublin, was one of an
ongoing series of free educational seminars on
water quality and the prevention and control of
waterborne pathogens.
www.specialistmasterclasses.com/
home.html
Susan Pearson BSc is a freelance journalist
specialising in medicine and the environment.
Waterborne Pseudomonas bacteria are a common source of infection in care settings.
SusanPearson reports
Cut it out: waterborne
Pseudomanas bacteria
can be blocked by
installing water filters
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