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Legionella spp. decontamination ineffective in potable water supply
Most cases of Legionella spp. identified in the hot water systems of buildings in a German community were unresponsive to thermal disinfection, according to research published in the American Journal of Infection Control.
“This study was designed as a prevalence survey and risk factor analysis focusing on the water systems rather than the users. It was not possible to compare the exposure in the buildings surveyed to the actual occurrence of clinical cases of legionellosis,” Eva-Brigitta Kruse MD, MPH, from Wisplinghoff Laboratories in Cologne, Germany, and colleagues wrote. “However, the data obtained in this survey provide a comprehensive overview of the exposure to different pathogenic Legionella spp. in the community and the limited effect of thermal disinfection, suggesting that a focus on checking up on and controlling the condition and correct operation of the hot water system in residential and other buildings is warranted.”
Kruse and colleagues performed a culture test of 4,482 water samples from 718 German buildings for Legionella spp., followed by a statistical analysis of potential risk factors for contamination, with a subgroup analysis of thermal disinfection within some buildings.
“For secondary outcomes, we investigated the proportions of positive samples and their distribution in the system, the prevalence of the different Legionella spp., the influence of a number of factors suspected to be associated with the risk of contamination, and the effectiveness of thermal disinfection (ie, superheat and flush) to decrease or remove Legionella contamination,” Kruse and colleagues wrote.
The researchers found 233 buildings with Legionella spp. (32.7%) and of these buildings, 148 (63.5%) had a medium or higher contamination level. The L. pneumophila species was present in 94% of cases.
Among contaminated buildings, there was a strong association with temperature in hot water circulation, specifically for temperatures between 30°C and 45°C; however, factors such as the time of year, building size, location of samples taken or transport time to the laboratory did not impact contamination. The researchers noted that attempts at thermal disinfection in 77 buildings were mostly unsuccessful; after disinfection, Legionella spp. still was detected in 62.3% of the structures. – by Jeff Craven
Disclosure: The researchers report no relevant financial disclosures.