36 ENVIRONMENT and ENERGY
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acquired legionnaires’ disease. The study was conducted at 20 hospitals in 13 states. None of the hospitals had previously experienced endemic hospital-acquired legionnaires’ disease. L. pneumophila and L. anisa were isolated from 14 hospital water systems. High-level colonisation of the premise plumbing system( defined as 30 % or more of the distal outlets being positive for L. pneumophila) was demonstrated for six of the 14 hospitals with positive findings. More than 600 patients were evaluated for legionnaires’ disease from 12 hospitals. Hospitalacquired legionnaires’ disease was identified in four hospitals, all of which had serogroup one in 30 % or more of the distal outlets.
Demirjian et al.( 2015) evaluated medical records and conducted an environmental assessment in a large Pennsylvania hospital to characterise a legionnaires’ disease outbreak that had occurred between 2011 and 2012. The authors also evaluated the contributing factors. As part of the hospital’ s legionella prevention protocol, they implemented monthly system-wide superheat and flush protocols if at least 30 % of the distal sites showed legionella growth,‘ until culture results returned to an acceptable level’( less than 30 % positive). Based on the 2011 – 2012 records, the authors found that all definite health care associated cases occurred when sampling results were far below the 30 % threshold. The authors concluded that definite health care associated cases occurred when only 4 % of distal sites were positive. In this outbreak, the level of legionella detected was < 10 CFU / mL in almost all the water samples. The authors also noted that quantitative culture results in general have poor precision and can vary within a range of 3-log CFU / mL of viable legionellae. CDC does not recognise a safe level of legionella.
A review by Allen et al.( 2012) also concluded that the 30 % threshold provides both low specificity( 74 %) and sensitivity( 59 %).
Using legionella test results as a measure of risk for disease transmission may be problematic due to knowledge gaps, including but not limited to, infectious dose, susceptibility of potential hosts, and virulence of the strain, as described in the following references:
• CDC and WHO recognise that environmental legionella counts alone cannot predict the probability of human infection from a water system, because other factors, such as the exposure dose and level of host susceptibility, contribute to the likelihood of infection( Demirjian et al., 2015; WHO, 2007; Sehulster and Chinn, 2003).
• The lack of reliable and definitive human infectious dose information for legionella makes environmental monitoring results difficult to translate into action levels that can directly reduce human health risks( Demirjian et al., 2015; Buse et al., 2012; Schoen and Ashbolt, 2011; Storey et al., 2004a; Storey et al., 2004b; O’ Brien and Bhopal, 1993; Fitzgeorge et al., 1983).
• While detection of legionella in a premise plumbing system may indicate conditions conducive to legionella persistence, some studies suggest that the strains of legionella detected during non-outbreak routine environmental testing may not be the strains usually known to cause disease( Kozak-Muiznieks et al., 2014; Euser et al., 2013; Harrison et al., 2009, Kozak et al., 2009; Doleans et al., 2004).
Current challenges to environmental testing for legionella include the following:
• Despite a number of published procedures for the detection of legionella in water samples, standard culture methods remain limited by their sensitivity and unreliability in detecting a wide range of legionella spp. on a consistent basis( Buse et al., 2012) and detecting VBNC legionella( Oliver, 2010). The time it takes to receive results limits the utility of testing. CDC has established the Environmental Legionella Isolation Techniques Evaluation( ELITE) Programme for the certification of laboratories that are proficient in legionella isolation by culture( http:// www. cdc. gov / legionella / elite. html). This is a voluntary programme to identify laboratories that use procedures that are consistent with federal recommendations, and meet or exceed industry standards for the recovery of legionella. Culture protocols include water sample treatment and isolate
April 2017 Volume 23 I Number 2 www. plumbingafrica. co. za