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HEALTH AND SANITATION
Where emergency remediation is required , raising the temperature of hot water tanks to 71 – 77 ° C and keeping the water temperature at outlets > 65 ° C during flushing are recommended .
• Darelid et al . ( 2002 ) reported the successful application of thermal shock disinfection after a 1991 nosocomial outbreak of legionnaires ’ disease in a Swedish hospital . The hot water temperature was raised from 45 ° C to 65 ° C ( 113 ° F to 149 ° F ) to maintain the circulating hot water temperature greater than 55 ° C ( 131 ° F ) to control the bacteria . Environmental monitoring was conducted over a 10-year period to confirm whether this thermal shock treatment was sufficient or if chemical disinfection was required . The monitoring results showed that complete eradication of legionella was not possible , but the occurrence of nosocomial legionnaires ’ disease was controlled by maintaining the circulating hot water temperature greater than 55 ° C ( 131 ° F ).
However , an inadequate temperature for the superheat ( less than 65 ° C , or 149 ° F ) or a short flush time ( such as five minutes ) is ineffective for the control of legionella , as experienced at some hospitals ( Chen et al ., 2005 ). Even 70 ° C may allow some bacteria to survive and acquire resistance ( Allegra et al ., 2011 ). The shock treatment may not provide long-term control of legionella if the premise plumbing system does not maintain a proper temperature or a residual chlorine level .
• Allegra et al . ( 2011 ) tested the heat susceptibility of legionella strains isolated from hot water in four hospital distribution systems over several years . The authors compared susceptibility of each group of strains using samples collected prior to and following heat treatment in the distribution system . They exposed legionella from each sample to 70 ° C ( 158 ° F ) for 30 minutes in the laboratory and determined the percentage of viable and VBNC cells remaining using flow cytometry . Strains of L . pneumophila serogroup 1 demonstrated highly variable heat resistance ( mean percentage of viable and VBNC cells ranged from 11.7 % to 71.7 %). One group of strains in one distribution system developed resistance over time , apparently in response to repeated heat shock , with the mean percentage of viable and VBNC cells increasing from 12.7 % to 70.5 %.
• Chen et al . ( 2005 ) conducted superheat-and-flush treatment on the water supply for a 1 070-bed medical centre in southern Taiwan . The treatment procedure involved removing faucet aerators and showerheads at distal sites , flushing distal sites with cold water for two minutes , and flushing distal sites with hot water at 60 ° C ( 140 ° F ) for five minutes . The procedure was conducted once a day for five consecutive days on each portion of the water system . Water samples were collected before treatment and 10 days after treatment . The first heat and flush treatment , performed over an eightweek period , controlled legionella in patient wards and reduced the colonisation rate in ICUs from 80 % to 25 %. But two months later , the colonisation rate had increased from zero to 15 % in patient wards , and from 25 % to 93 % in the ICUs . The second superheat-and-flush treatment , performed over a two-day period , resulted in much smaller reductions in the colonisation rate .
• Stout et al . ( 1998 ) compared the effectiveness of superheat-and-flush to CSI for controlling legionella in the Pittsburgh Veterans ’ Affairs Health Care Center . There was an average of six cases of legionnaires ’ disease per year for the 13 years when superheat-and-flush was employed , as compared to two cases per year for the three years when CSI was used . The percentage of distal sites positive for L . pneumophila was 15 % for superheat-and-flush compared to 4 % for CSI . Because the conditions during the two study periods may not have been comparable , the authors used findings from another hospital study for verification ( Mietzner et al ., 1997 ). Stout et al . ( 1998 ) concluded that a properly maintained and monitored CSI system was more effective than the superheat-and-flush method .
• Mietzner et al . ( 1997 ) conducted thermal treatment of a hot water circuit in a hospital by flushing hot water (> 60 ° C , or > 140 ° F ) through distal fixtures for 10 minutes . Sampling of the faucets showed that positive samples decreased from approximately 80 % to 1 or 2 % of samples immediately following the initial treatment , then increased to 36 % within 61 days of the treatment . Three additional heatflush treatments resulted in zero detection of L . pneumophila . But recolonisation occurred within 29 days of the last treatment . The heat-flush treatment failed to provide long-term control of L . pneumophila .
Combining the superheat-and-flush method with supplemental continuous chlorination ( Cristino et al ., 2012 ; Heimberger et al ., 1991 ; Snyder et al ., 1990 ) or UV light irradiation ( Liu et al ., 1995 ) has achieved some success in decontaminating hospital water systems .
• Cristino et al . ( 2012 ) reported the successful application of various shock disinfection methods ( for example heat shock , chemical shock with peracetic acid and chlorine dioxide ) followed by continuous chlorination for long-term care facilities , including three hot water systems that were colonised by L . pneumophila and one hot water
October 2017 Volume 23 I Number 8 www . plumbingafrica . co . za