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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