Dishwashers identified as reservoir for Legionella
WASHINGTON, D.C. — Researchers in Japan have identified dishwashers as a reservoir for strains of Legionella bacteria that contaminated two tap water sources in a hospital, according to a presentation at ICAAC 2014.
Legionella bacteria were found in the hospital staff areas during an annual water inspection in 2011, leading the investigators to conduct two studies to determine whether contamination was a widespread problem. They conducted a retrospective descriptive study of 5 years of medical records of patients hospitalized from 2006 to 2011. They also conducted an environmental building inspection to identify other areas of contamination in the water system.
They found no evidence of patient infections during the investigation period. They collected specimens from 17 faucets in the inpatient and staff areas and from the 14 dishwasher connections that were all in the staff areas.
Five of the 17 faucets and seven of the 14 dishwasher connectors were contaminated with Legionella species. None of the contaminated faucets were from inpatient areas. Isolates from three of the faucets and all of the dishwashers were identified as L. pneumophila SG6. The five contaminated faucets were connected to the same hot water pipelines as the seven dishwashers. The L. pneumophila SG6 strains isolated from the faucets and dishwashers were identified using PCR.
According to the researchers, all of the dishwashers were immediately removed, and the hot water supply underwent a thorough cleaning and decontamination. Since then, all cultures have been negative. The researchers said the water temperature in the peripheral hot water pipeline was lower than the temperature of the central system, and the chlorine concentration in such systems is lower.
“Lower temperature and lower chlorine concentrations are the cause of biofilm growth,” the researchers wrote. “These conditions might allow the growth of bacteria in peripheral hot water pipelines.”
For more information:
Yoshida M. Abstract K-1677. Presented at: Interscience Conference on Antimicrobial Agents and Chemotherapy; Sept. 5-9, 2014; Washington, D.C.
Disclosure: The researchers report no relevant financial disclosures.