Objective: To investigate the prevalence of L. pneumophila contamination and maintenance characteristics of cooling towers setting in selected places, Bangkok.

Material and Method: A cross-sectional survey of 72 cooling towers from 4 hospitals (21 cooling towers), 7 department stores (35 cooling towers), 3 hotels (16 cooling towers) in Bangkok for L. pneumophila contamination and maintenance characteristics was carried out. Two or three water samples were collected from the studied cooling towers to culture for Legionella spp. and confirmed by real-time Polymerase Chain Reaction (PCR). Data for maintenance characteristics of studied cooling towers were collected from officers who were responsible for cooling tower maintenance.

Results: Most (71.4-87.5%) cooling tower models were cross-flow types, and most (81-100%) received the maintenance ≥2 times/year. About 50-80.9% were not added with biocide or ozone to inhibit the growth of Legionella spp. Totally, 27.8% of cooling towers were contaminated with L. pneumophila. The cooling towers in hospitals had the highest contamination (42.9%). Cooling towers with size <500 tons, use duration ≥5 years, and maintenance frequency <2 times/year had higher contamination. However, most contaminated cooling towers did not receive any biocides.

Conclusion: Although most cooling towers received frequent maintenance, most of those that were contaminated with L. pneumophila were not treated with biocides. The use of biocides should be considered during cooling tower maintenance.