Legionella pollution in cooling tower water of air-conditioning systems in Shanghai, China

Abstract

Aims: To determine Legionella pollution prevalence, describe the amount of Legionellae with respect to temperature in Shanghai cooling tower water (CTWs) in various types of public sites. Methods and Results: Six urban districts were selected as the study fields, adopting multiple-phase sampling methods. Routine culture was used to identify Legionellae. Of the samples, 58.9% (189/321) were observed to be positive, 19.9% were isolated over 100 CFU ml-1. Legionella pneumophila serogroup 1 was the most frequently isolated species (155/189, 82.0%), followed by Leg. micdadei that was at the second place (44/189, 23.3%). The mean CFU ml-1 of Legionellae in CTWs reached its peak from July to September. Over all 15.4% of the samples exceeding 100 CFU ml-1 were observed in a hospital setting. Conclusions: The prevalence of Legionella pollution in CTWs, especially in CTWs of subway stations and hospitals, is worrying, and the positive rate and CFU ml-1 of Legionellae in CTWs have a close relationship with air temperature. Significance and Impact of the Study: The study demonstrates pollution prevalence rates in different types of sites and various seasons, and provides a proportion of different serogroups of Legionellae. It illuminates an urgent need for dealing with the potential risk of legionellosis in Shanghai, through improved control and prevention strategies. © 2008 The Authors.