HEALTH AND SANITATION
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system colonised by L. londiniensis. No
cases of hospital-acquired legionellosis
occurred during the study period.
Although three of four systems reported
that 100% of samples were positive
for legionella before and after shock
treatment, the mean legionella count
was reduced by up to 69% as a result
of shock disinfection. Two years of
environmental monitoring after shock
disinfection showed that legionella counts
either continued to decrease or remained
at post-treatment levels.
Liu et al. (1995) conducted superheat-
and-flush and shock chlorination
treatment prior to UV treatment of a
hospital’s hot and cold water systems.
Five years of surveillance data at
untreated control sites (three showers
and 20 other water outlets) showed
that 30–80% of sites were persistently
colonised with L. pneumophila (that is,
1–300CFU per swab). The UV treatment
units were located near points of use
such as showers. Filters were added to
prevent scale accumulation on the UV
lamps. The study showed that UV plus
pre-filtration could prevent legionella
recolonisation for three months after
shock treatment.
Heimberger et al. (1991) reported the
successful application of hot water
flushing and supplemental chlorination
to control legionella at a tertiary care
hospital in Syracuse, New York. L.
pneumophila was found in 6 of 32
water samples, including samples
from one of two hot water tanks. Initial
treatment of the hot water system
included tank cleaning, hot water
flushing and shock chlorination but did
not include continuous supplemental
chlorination. One month after initial
treatment, L. pneumophila was again
detected from a hot water tank and
several taps, and another case of
legionellosis occurred. In response, hot
water flushing, shock chlorination, and
continuous supplemental chlorination
were conducted. On a monthly basis,
each hot water tank is taken offline,
cleaned and treated with hot water. In
the 7.5 months after these practices
were employed, all samples were
www.plumbingafrica.co.za
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negative for legionella and no new
cases of legionellosis had occurred.
Snyder et al. (1990) reported a successful
application of heat flushing followed by
continuous supplemental chlorination to
reduce L. pneumophila in a hospital hot
water system. Twelve of 74 sampling
sites in the hot water system were
culture-positive for L. pneumophila.
Heat flushing (>60°C, or >140°F) at
hot water system outlets for 30 minutes
alone reduced the number of legionella-
positive samples by 66%, but within four
months, the number of positive samples
had increased. Continuous supplemental
chlorination was added to the hot water
system at a dosage rate of 2mg/L. After
six weeks, the number of legionella-
positive samples decreased from 37%
(43 of 115 samples) to 7% (8 of 115
samples). After 17 months of continuous
supplemental chlorination, no new cases
of legionellosis had occurred.
POTENTIAL WATER QUALITY ISSUES
• Regrowth of legionella following
superheat-and-flush has been identified
as an issue (Chen et al., 2005; Stout
and Yu, 2003). Recolonisation could
be caused by the survival properties of
legionella (that is, the ability to colonise
biofilms, ability to parasitise and multiply
within protozoa, and ability to enter
a VBNC state), or failure to properly
address the conditions that caused the
problem (such as dead ends and long
water residence times). Researchers
have revealed that L. pneumophila can
rapidly proliferate after temperatures
are lower ed, presumably via microbial
response to the nutrients released by
the newly killed biofilm (necrotrophy)
(Temmerman et al., 2006). This finding
indicates that disturbing the microbial
ecology on a short-term basis may
exacerbate pathogen regrowth in the
long-term (Pruden et al., 2013).
The EPA advises facility owners or operators
who are considering adjustments to their
premise plumbing system to consult with their
primacy agency for any specific considerations
or requirements that may apply, including
plumbing code requirements. PA
October 2017 Volume 23 I Number 8