ENUMERATION OF LEGIONELLA PNEUMOPHILA IN COOLING TOWER WATER SYSTEMS IRFAN TÜRETGEN ∗ , ESRA ILHAN SUNGUR and AYSIN COTUK Department of Biology, Faculty of Science, Istanbul University, Istanbul, Turkey ( ∗ author for correspondence, e-mail: turetgen@istanbul.edu.tr) (Received 25 March 2003; accepted 12 November 2003) Abstract. Legionella pneumophila, the causative agent of Legionnaires’ disease, is known to colo- nise and frequently grow in cooling tower waters. Disease is acquired by inhaling aerosol contami- nated by legionellae. Determination of the count of Legionella pneumophila in cooling tower waters may, therefore, be useful for risk assessment. In our survey, 103 water samples from 50 cooling towers were examined over a five-year period to indicate the seasonal distribution and the ecology of L. pneumophila, as regards temperature and pH. L. pneumophila serogroup 1 was found in 44% of the isolated strains, which is primarily responsible for the majority of Legionnaires’ disease. The large majority of examined towers had levels of L. pneumophila in the high-risk category. These cooling towers have been linked to many outbreaks of Legionnaires’ disease. Keywords: aerosol, cooling tower, Legionnaires’ disease, Legionella pneumophila, risk assessment Environmental Monitoring and Assessment (2005) 100: 53–58 © Springer 2005 1. Introduction Legionella pneumophila, the agent responsible for Legionnaires’ disease and Pon- tiac fever (Yu, 1993), was first discovered in a 1976 outbreak in Philadelphia. This bacterium has been found in various aquatic environments, e.g., ponds, rivers, lakes (Yamamoto et al., 1992) as well as in soil. L. pneumophila, for which 14 serogroups have been identified, is the species most commonly associated with dis- ease outbreaks (Benson and Fields, 1998). L. pneumophila does not pose a serious health risk due to its low amounts in natural habitats. However, man-made systems serve as amplifiers for L. pneumophila by providing suitable conditions for growth and multiplication (Bentham, 2000). Numerous epidemic investigations have con- vincingly demonstrated that cooling towers have served as sources of Legionella infection (Bosch, 2001; Garbe et al., 1985). Frequently, Legionella has been iso- lated in high numbers from water, sediments (Atlas, 1999) and slimes in cooling water systems (Bentham, 2000). Cooling towers are heat rejection systems and provide cooling water for a wide variety of applications. These applications include refrigeration plant, water-cooled air compressors, telecommunication devices, and other industrial processes in which heat is generated (Broadbent, 1993). Contaminated aerosols, which are generated from cooling tower fan, acquire the infection and inhalation of these aerosols presumably produces Legionnaires’