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

**David Pierre 1, Julianne L. Baron 1, Xiao Ma 1, Frank P. Sidari III 1, Marilyn M. Wagener 2 and Janet E. Stout 1,3,\***


Received: 26 November 2019; Accepted: 11 December 2019; Published: 13 December 2019

**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 sugges<sup>t</sup> 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 sugges<sup>t</sup> 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 managemen<sup>t</sup> programs.

**Keywords:** *Legionella*; distal site positivity; hot water return line; chlorine; HPC; temperature; water managemen<sup>t</sup>
