Two-year evaluation of Legionella in an aging residential building: Assessment of multiple potable water remediation approaches.

Legionella is an opportunistic waterborne pathogen that is difficult to eradicate in colonized drinking water pipes. Legionella control is further challenged by aging water infrastructure and lack of evidence-based guidance for building treatment. This study assessed multiple premise water remediation approaches designed to reduce Legionella pneumophila within a residential building located in an aging, urban drinking water system over a two-year period. Samples (n = 745) were collected from hot and cold-water lines and quantified via most probable number culture. Building-level treatment approaches included three single heat shocks, three single chemical shocks, and continuous low-level chemical disinfection in the potable water system. The building was highly colonized with L. pneumophila with 71 % L. pneumophila positivity. Single heat shocks had a statistically significant L. pneumophila reduction one day post treatment but no significant L. pneumophila reduction at one week, two weeks, and four weeks post treatment. The first two chemical shocks resulted in statistically significant L. pneumophila reduction at two days and four weeks post treatment, but there was a significant L. pneumophila increase at four weeks following the third chemical shock. Continuous low-level chemical disinfection resulted in statistically significant L. pneumophila reduction at ten weeks post treatment implementation. This demonstrates that in a building highly colonized with L. pneumophila, sustained remediation is best achieved using continuous low-level chemical treatment.