ENVIRONMENT and ENERGY
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Legionella occurrence and risk
Premise plumbing systems have been identified as a source of legionella infection( Stout et al., 1992; Muder et al., 1986). Within healthcare facilities such as hospitals and nursing homes, potable water supply is the most common source of exposure( Lin et al., 2011a). Exposure to legionellae has also been associated with other types of premise plumbing systems( such as hotels and other buildings with complex water distribution systems)( Silk et al., 2012; Hung et al., 1993; Tobin et al., 1981a and 1981b).
By the Environmental Protection Agency
The European Centre for Disease Prevention and Control( ECDC) reports that 58 % of sampling sites that tested positive for legionella in 2014 were from cooling towers and 26 % were from water systems, including 66 hot water systems, 31 cold water systems, and 184 non-specified water systems( ECDC, 2016).
Legionella species are known to be present in finished water from water treatment plants( Lu et al., 2016; Buse et al., 2012) and can persist and grow in the biofilms of municipal water distribution systems( Lu et al., 2016; Wingender and Flemming, 2011; States et al., 1987). Lu et al.( 2015) identified diverse legionella species, including L. pneumophila, L. pneumophila sg1, and L. anisa, in sediment samples from municipal drinking water storage tanks in 18 locations and across 10 states. In the Lu et al.( 2015) study, quantitative polymerase chain reaction( qPCR) was used instead of a culture-based approach, and legionella species were detected with a frequency of approximately 67 %. A co-occurrence of Acanthamoebae and legionella was observed. Quantitative PCR-based monitoring complements culturebased methods in the presence of disinfectants that affect cell culturability( Bédard et al., 2016).
Schwake et al.( 2016) conducted two surveys of tap water: one in small buildings( for example single- storey homes and businesses) and the other in two hospitals in Flint, Michigan. They found L. pneumophila in the two hospitals but not in the small buildings. Schwake et al.( 2016) looked at linkages between a legionella outbreak and changes in municipal water quality, and operational changes in the distribution system. The study mentions that water utilities may have a role to play in controlling proliferation of pathogens in premise plumbing.
Further, L. pneumophila can form biofilm from secreted substances( that is, extracellular polymeric substances) and can multiply within such biofilms( Mampel et al., 2006). Therefore, biofilms in municipal drinking water systems can be a potential source of water contamination( Wingender and Flemming, 2011) and drinking water from municipal systems can possibly contaminate the premise plumbing systems in hospitals and other buildings with L. pneumophila( Donohue et al., 2014; States et al., 1987).
Several surveys have found legionella in premise plumbing systems, including in buildings that had not been linked to recognised outbreaks:
• Bartley et al.( 2016) traced the epidemiology of two nosocomial( hospital-acquired) cases of legionnaires’ disease at a hospital in Australia. Whole genome sequence analysis was performed on L. pneumophila isolates from the patients infected in 2013. The genome sequences were found to be closely related to those of isolates from the hospital water distribution system and to retrospective isolates from a patient infected in 2011.
• Bédard et al.( 2016) found L. pneumophila in the hot water system of a hospital from 85 % of sampled taps despite copper treatment. A significant decrease in L. pneumophila count by culture was observed following heat shock disinfection. Ongoing corrective measures were implemented, which included increasing the hot water temperature from 55 to 60 ° C, flushing taps weekly with hot water, removing excess lengths of pipe, and maintaining a temperature of 55 ° C throughout the system. A low level of contamination remained in areas with hydraulic deficiencies.
• Rhoads et al.( 2016a) studied L. pneumophila trends in controlled, replicated pilot-scale hot water systems with continuous recirculating lines. They demonstrated the potential for thermal control strategies to be undermined by distal taps and corrective mixing. Rhoads et al.( 2016b) surveyed a cross-section of green buildings and compared them to conventional buildings. They found increased water age, and decreased chlorine and chloramine residuals in the green buildings, as well as increased levels of total bacteria 16S rRNA genes and increased levels of gene markers for
Continued on page 31 >> www. plumbingafrica. co. za February 2017 Volume 22 I Number 12