Water Quality as a Predictor of Legionella Positivity of Building Water Systems

Abstract

Testing drinking water systems for the presence of Legionella colonization is a proactive approach to assess and reduce the risk of Legionnaires’ disease. Previous studies suggest that there may be a link between Legionella positivity in the hot water return line or certain water quality parameters (temperature, free chlorine residual, etc.) with distal site Legionella positivity. It has been suggested that these measurements could be used as a surrogate for testing for Legionella in building water systems. We evaluated the relationship between hot water return line Legionella positivity and other water quality parameters and Legionella colonization in premise plumbing systems by testing 269 samples from domestic cold and hot water samples in 28 buildings. The hot water return line Legionella positivity and distal site positivity only demonstrated a 77.8% concordance rate. Hot water return line Legionella positivity compared to distal site positivity had a sensitivity of 55% and a specificity of 96%. There was poor correlation and a low positive predictive value between the hot water return line and distal outlet positivity. There was no correlation between Legionella distal site positivity and total bacteria (heterotrophic plate count), pH, free chlorine, calcium, magnesium, zinc, manganese, copper, temperature, total organic carbon, or incoming cold-water chlorine concentration. These findings suggest that hot water return line Legionella positivity and other water quality parameters are not predictive of distal site positivity and should not be used alone to determine the building’s Legionella colonization rate and effectiveness of water management programs.

Legionella Diversity and Spatiotemporal Variation in the Occurrence of Opportunistic Pathogens within a Large Building Water System

“…However, these correlations were location and sample type specific with conflicting positive and negative correlations for turbidity and HPC. Conflicting correlations between the latter and Legionella levels have been reported previously with either strong correlations [81], no correlations [82][83][84][85], or possible seasonal dependencies for these correlations [7]. Other conflicting correlations were reported between Legionella occurrence and pH, temperature, various minerals and metals (Ca, Cu, Fe, Mg, Mn, and Zn), total organic carbon, conductivity, and free chlorine at the sampling site and building supply feed [85][86][87].…”

Environmental Management of Legionella in Domestic Water Systems: Consolidated and Innovative Approaches for Disinfection Methods and Risk Assessment

“…Furthermore, recently no significant correlation between distal site Legionella positivity and hot water return line temperature has been found. In particular, also buildings with a hot water return temperature >51.1 °C have been found positive for the bacterium in distal sites [ 14 ]. These findings imply not only that temperature should not be used alone to predict the presence or absence of Legionella in a drinking water distribution system, but also that it is crucial to evaluate the effectiveness of the applied thermal water management program.…”

Biogeography and Environmental Drivers of Legionella pneumophila Abundance and Genotype Composition across the West Bank: Relevance of a Genotype-Based Ecology for Understanding Legionella Occurrence

“…In general, an impact of magnesium on Legionella abundance has not yet been demonstrated so far. There were large-scale investigations in residential drinking water distribution systems (DWDS) that included magnesium in the overall analysis of environmental drivers for Legionella abundance [35,36]. However, due to low magnesium concentrations in these DWDS (<3 mg/L), an effect of magnesium was not observed.…”