Use of terminal tap water filter systems for prevention of nosocomial legionellosis.

Hospital water supplies often contain Legionella spp. and represent a potential source of nosocomial infection, especially for immunocompromised patients or those in intensive care units. Therefore, pathogen-free water should be provided for such high-risk patients. Surveillance of splash water was performed in high-risk patient care areas at Berlin Charité-University Medicine (506 samples) and Medical School Hannover (767 samples) to investigate the ability to provide water that was free from Legionella spp. by the use of disposable, terminal tap water filter systems with non-impregnated, as well as impregnated, filters with prolonged usage intervals. Twenty (Berlin) and 32 (Hannover) water outlets were provided with disposable filters with a pore size of 0.2 microm. Testing of unfiltered tap water revealed growth of Legionella spp. in 53 of 210 (Berlin) and 30 of 32 (Hannover) samples. Non-impregnated, terminal, disposable water filters at taps used for high-risk patient care led to water free from Legionella spp. in 154 of 155 (99.4%) samples after three to four days and in 137 of 141 (97.2%) samples after six to seven days. When testing a new impregnated filter, 255 of 256 (99.6%) samples remained free from Legionella spp. after continuous use for seven days, as recommended by the manufacturers, and also after 10 days. Samples that were positive for Legionella spp. contained 1-4 cfu/mL. We believe that an impregnated filter system is suitable for the prevention of nosocomial Legionellosis in high-risk patient care areas.