Health and sanitation
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POU filtration devices have been certified by NSF International
for removal of protozoa, bacteria, and viruses in general, using
surrogate microorganisms as challenge organisms during
testing and evaluation.
Characterisation of effectiveness against
legionella
Several case studies describe the effectiveness of POU
membrane filtration devices for removal of legionella.
• Casini et al. (2014) reported the efficacy of POU filtration
installed in selected wards of an Italian hospital to further
reduce legionella growth within the building hot water
system after chloride dioxide disinfection. POU filters
used in this study had a 0.2-µm nominal pore size and
30-day replacement rate. This integrated disinfection-
filtration strategy, although expensive, significantly reduced
legionella counts to less than 10 3 CFU/L and achieved a
positive sample rate of less than 30%.
• Baron et al. (2014b) evaluated a new faucet filter at five
sinks in a cancer centre and found that legionellae were
removed from all filtered samples for 12 weeks, exceeding
the manufacturer's recommended maximum duration of
use of 62 days. The filters contain a 30-µm pre-filtration
layer, a 1-µm membrane, and a 0.2-µm membrane.
• Marchesi et al. (2011) performed a 10-year review of
multiple treatment methods to control for legionella at a
hospital in Italy, including POU filtration, though information
on the characteristics of the filters was not supplied. Filters
were placed in high-risk units of the hospital only, where
high levels of legionella contamination were identified, and
were replaced every 30 days. No legionellae were detected
at taps containing POU filters.
• Daeschlein et al. (2007) evaluated a reusable POU filter for
removing waterborne pathogens, including L. pneumophila,
in a hospital’s transplant unit for eight weeks. Filters had
three configurations: (1) hollow fibre of polyethersulfone with
pore size 0.2µm and surface area of 800 cm 2 ; (2) hollow
fibre of polyethersulfone with pore size 0.2µm, surface area
of 1100 cm 2 , and inner encasement coated with nanosilver;
and (3) same as (2) with metallic silver outlet.
Filters were placed on 18 taps (12 taps, six showers) in
the hospital’s transplant unit and each filter was monitored
for pathogens at one, four and eight weeks, reprocessed and
reused in three additional trials.
Over the test period, no legionella or other pathogens
were detected in any filter effluent. Because bacterial counts
in filtered water exceeded the limit of >100 CFU/mL eight
times, the following criteria were developed to prevent carry-
over contamination from reuse of the filters: filters were
cleaned with a strong chemical followed by flushing and
thermal disinfection in a quality control-compliant washer-
disinfector once a week, in addition to alcohol disinfection of
the filter encasement.
With this reprocessing, the authors determined that filters
should be changed after four weeks in high-risk areas and
after eight weeks in moderate-risk areas.
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A newer versi on of the filters described in the example
by Daeschlein et al. (2007) was evaluated by Vonberg
et al. (2008) at a hospital in Germany. The new version
had a membrane surface coated with nanosilver. Fifteen
taps in a thoracic surgery department were selected and
sampled before adding filters.
Filters were placed on those taps and sampled after
one, two, three and four weeks of usage. Samples
were analysed for the pathogens legionella and
pseudomonas, in addition to the indicators enterococci
and heterotrophic bacteria. Legionellae were detected
in nearly half (48.3%) of taps before filters were added
and only one sample (week 1) after filters were added (L.
pneumophila serogroup 1, 4 CFU/mL); no pseudomonas
were detected.
The authors did not attempt to reprocess the filters as
in the Daeschlein study and did see heterotrophs increase
to >100 CFU/mL in some filters after one week of use.
The authors concluded that incorporation of nanosilver in
the filter’s membrane surface coating may prevent biofilm
growth in this POU device and that use of these POU filters
with weekly replacement in high-risk patient wards may be
effective at preventing nosocomial legionellosis.
Sheffer et al. (2005) evaluated POU filtration devices
containing positively charged nylon membranes with
a 0.2-µm nominal pore size. Filters were placed on
four taps in the administration building at a hospital
and monitored for legionella, heterotrophic bacteria,
and mycobacteria, along with three taps without filters,
every 2–3 days for 13 days, before and after a one-
minute flush.
Samples from taps with filters before flush were
negative for legionella during the 13-day period, while
mean concentration in taps without filters was 104.5 CFU/
mL. Mycobacterium gordonae was isolated from 10.3%
of taps without filters before flushing, but no mycobacteria
were isolated from taps with filters before flushing.
Heterotrophs were significantly reduced at taps with
filters. One post-flush sample from a tap with a filter was
positive for legionella on day 10, with a concentration
of 5 CFU/mL. No post-flush samples from taps with
or without filters were positive for mycobacteria. The
authors concluded that the POU filters used in this study
effectively controlled legionella and mycobacteria through
seven days of use.
Molloy et al. (2008) evaluated three types of POU
solid block activated carbon filters for removal of
L. pneumophila in a laboratory-simulated domestic
water system: (1) carbon containing copper, (2) carbon
containing copper and silver, and (3) carbon without
metals. Filters were challenged with tap water seeded
with L. pneumophila multiple times and water was
monitored under simulated domestic use for six weeks.
Levels of legionella were reduced by all three filters by
nearly 8 log (99.999999%), but they were detected in
all filter effluents for the length of the study. The authors
concluded that the organisms attached to the carbon
blocks and sloughed off over time. PA
September 2017 Volume 23 I Number 7