Characteristics of Cooling Towers and Evaporative Condensers and Presence of Legionella in Water

Abstract

P-721 Introduction: Cooling towers and evaporative condensers are elements associated with cooling and refrigeration systems. Many legionella outbreaks have been linked to this type of installations. To minimise the risk of legionella transmission, the Spanish Ministry of Health and Consumption published Royal Decree 865/2003, which establishes the preventive design and surveillance system to be fulfilled by these installations. With the aim of assessing the degree of fulfilment (infrastructure, maintenance, cleaning, disinfection) of the mentioned installations in Gipuzkoa (the Basque Country, Spain), they were characterised and the water in the cooling circuits was checked for legionella. Methods: Over the period 2002–2004, 297 cooling circuits were visited and characterised. A survey gathered information on three variables: infrastructure, maintenance of circuits and water quality control. The sampling and analysis of the water was carried out in two points of the cooling circuit (the tray and the bleeder valve). The Legionella analysis was conducted according to the ISO 11734 standard. Results: 260 (87.5%) of installations carried out maintenance operations; 243 (81.8%) had a continuous treatment of the water in the circuits and 270 (90.9%) cleaned and disinfected the circuits periodically. Out of the 200 samples taken, 72 (36%) were positive (detection limit 100 u.f.c/l) for Legionella spp and 56 (28%) were positive for L. pneumophila. The cooling towers which did not incorporate a stop mode proved to be more risky for Legionella spp. (O.R: 4.89; IC: 1.17–20.38) and for L. pneumophila (O.R: 3.56; IC: 0.86–14.85)than those which incorporated this mode. Four factors were identified as protective against Legionella spp.: collecting the water from the municipal network (O.R: 0.46; IC: 0.24–0.86); having circuits which are accessible for cleaning (O.R: 0.32; IC: 0.10–0.94); conducting periodical cleaning and shock disinfections in the circuits (O.R: 0.17; IC: 0.04–0.64), and carrying out a continuous treatment of the water by using a disinfectant with residual power (O.R: 0.40; IC:0.15–0.83). In the case of L. pneumophila, two protective factors were identified: collecting the water from the municipal network (O.R: 0.35; IC: 0.18–0.68), and carrying out a continuous treatment of the water by using a disinfectant with residual power (O.R: 0.25; IC:0.08–0.0.83) Discussion and Conclusions: Designing the installations properly, using water coming from the municipal net work, periodically cleaning and disinfecting the circuits and treating the water they contain by means of disinfectant products with residual power reduces the prevalence of Legionella in water.