Comparative assessment of chlorine, heat, ozone, and UV light for killing Legionella pneumophila within a model plumbing system

Abstract

Nosocomial Legionnaires disease can be acquired by exposure to the organism from the hospital water distribution system. As a result, many hospitals have instituted eradication procedures, including hyperchlorination and thermal eradication. We compared the efficacy of ozonation, UV light, hyperchlorination, and heat eradication using a model plumbing system constructed of copper piping, brass spigots, Plexiglas reservoir, electric hot water tank, and a pump. Legionella pneumophila was added to the system at 107 CFU/ml. Each method was tested under three conditions; (i) nonturbid water at 25°C, (ii) turbid water at 25°C, and (iii) nonturbid water at 43°C. UV light and heat killed L. pneumophila most rapidly and required minimal maintenance. Both UV light and heat (60°C) produced a 5 log kill in less than 1 h. In contrast, both chlorine and ozone required 5 h of exposure to produce a 5 log decrease. Neither turbidity nor the higher temperature of 43°C impaired the efficacy of any of the disinfectant methods. Surprisingly, higher temperature enhanced the disinfecting efficacy of chlorine. However, higher temperature accelerated the decomposition of the chlorine residual such that an additional 120% volume of chlorine was required. All four methods proved efficacious in eradicating L. pneumophila from a model plumbing system.