Analysis of the impact of a new electro-chemical activation system for potable water disinfection on the Legionella pneumophila isolation rate in a Spanish hospital

In a field study comparing isolation rates pre- and post-installation of an electro-chemical activation system for Legionella pneumophila disinfection of potable hot water in a Spanish hospital, a total of 250 tap samples pre-installation and 113 post-installation were collected. Chlorine levels were higher (p < 0.001) post-installation (0.55 ± 0.41 vs. 1.19 ± 0.44 ppm). Of 38.0% (138/363) samples positive for L. pneumophila, 111 (80.4%) were serogroups 2—14. Post-installation, the isolation rate was lower (46.8% vs. 18.6%; p < 0.001, odds ratio (OR) 0.26, 95% confidence interval (CI) 0.15—0.44) due to significant (p < 0.001; OR 0.25, 95% CI 0.14—0.45) reduction in L. pneumophila serogroups 2—14 from 38.4% to 13.3%. Post-installation, isolation rates were lower in spring (44.4% vs. 0.0%; p < 0.001), summer (80.0% vs. 25.0%; p = 0.003) and autumn (72.0% vs. 28.9%; p = 0.018), but not in winter (18.5% vs. 11.8%; p = 0.688). The seasonal wave constructed with pre-installation data significantly decreased post-installation by decreasing isolation rates in summer and autumn to rates similar to those found in winter pre-installation.