EFFICACY OF ULTRAVIOLET-LIGHT IN PREVENTING LEGIONELLA COLONIZATION OF A HOSPITAL WATER DISTRIBUTION-SYSTEM

We performed a controlled evaluation of ultraviolet light irradiation of hot and cold water supplies in a hospital colonized with Legionella by inserting the u.v. units near the ''point-of-use''. Showers on one wing of a hospital were supplied with u.v.-irradiated water. Showers on another wing and 20 other outlets served as controls. Cultures prio r to the installation of u.v. units showed all outlets to be heavily c olonized with L. pneumophila. Despite disinfection of incoming water b y u.v., Legionella in established niches of the plumbing system contin ued to survive. Superheat/flush and chlorination was then applied prio r to u.v. activation. Although cultures became negative initially, rec olonization occurred after 1 month. Scale accumulation on u.v. lamps h ad compromised the efficacy of u.v. irradiation. Filters were added to prevent scale accumulation on the u.v. lamps and the u.v.-supplied sh owers remained Legionella-free. U.V. plus prefiltration can prevent Le gionella recolonization for at least 4 months after disinfection if th e u.v. units are installed near the ''point-of-use''. Disinfection mus t be directed not only at incoming water, but also at established nich es within the existing plumbing system. The advantages of u.v. include easy installation, low expense, and no adverse effects on water or pl umbing.