HEALTH AND SANITATION
31
<< Continued from page 29
POTENTIAL WATER QUALITY ISSUES
Regrowth of legionella following superheat-
and-flush has been identified as an issue.
Recolonisation could be caused by the
survival properties of legionella (i.e., the
ability to colonise biofilms, ability to parasitise
and multiply within protozoa, and ability to
enter a viable but nonculturable (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 lowered, presumably via
microbial response to the nutrients released
by the newly killed biofilm (necrotrophy).
This finding indicates that disturbing the
microbial ecology on a short-term basis
may exacerbate pathogen regrowth in the
long term. 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.
OPERATIONAL CONDITIONS
The superheat-and-flush method generally
does not require special equipment;
however, it is labour-intensive and time-
consuming due to the need to monitor
hot water temperature and flushing time.
Several limitations of the superheat-and-
flush method need to be recognised:
• Superheat-and-flush is only effective
when the water temperature at
distal outlets reaches the required
temperature and the flushing is
conducted for the required duration.
Superheat-and-flush requires sufficient
hot water heating capacity. Superheat-
and-flush requires considerable energy
and manpower resources.
• Thermal disinfection will not disinfect
downstream of thermostatic mixer
valves and so is of limited value where
such valves are installed.
• Scalding is a significant hazard.
Caution and close supervision
must be taken during emergency
disinfection to protect patients, staff,
and visitors from scalding.
www.plumbingafrica.co.za
Recommendations for conducting an
effective superheat-and-flush, based on
the published standards and guidelines, are
summarised as follows:
• When possible, perform flushing when
the fewest building occupants are
present (e.g., nights and weekends).
• Post signage and warning notices
at all areas of the building to alert
occupants of the potential scalding
hazard.
• Maintain water heater temperatures
at 71–77 degrees C (160–170
degrees F) while progressively flushing
each outlet in the system for up to
30 minutes at 65 degrees C (149
degrees F).
• Flushing multiple outlets
simultaneously can save time, but
should not exceed the capacity of the
water heater and the flow capacity of
the system.
• Perform flushing in a manner that
reduces the risk of scalding and
aerosolisation of potable water in
patient-care areas.
• Following superheat-and-flush
treatment, maintain hot water system
temperature >60 degrees C (140
degrees F) in all hot water lines.
At the end of the procedure, collect
samples of water at distal outlets of the
water system. After the water temperature
has returned to normal, legionella culture
should be performed within two to seven
days to determine efficacy of the treatment;
the delay in testing is intended to reduce
false negative results caused by VBNC
cells. Culture should be repeated within
two weeks of treatment to determine if
there is any short-term control. Repeat
the procedure until decontamination is
achieved. Following decontamination,
microbiological checks must be repeated
periodically. PA
The superheat-and-
flush method generally
does not require special
equipment.
April 2018 Volume 24 I Number 2