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.
This is an open access article distributed under the Creative Commons Attribution License
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.