Introduction: The use of biocides is very important for controlling Legionella contamination in evaporative cooling systems. This study is a systematic review of research studies that evaluated the effectiveness of biocides in evaporative cooling systems for Legionella control. Methods: Published journal articles, dating from 1980-2008, were included if theses studies were field test of biocides against Legionella in operating cooling systems or tests preformed in a model cooling system that was spiked with Legionella spp. or used actual cooling water collected from an operating cooling system. Results: Of the 52 journals produced from the systematic review, 20 articles meet the inclusion criteria. The types of biocide studies included 9 articles that tested only chemical biocides, 3 articles that tested only non-chemical biocides, and 8 articles that compared chemical and non-chemical biocides. Discussion: The common end point for most of these studies was the measured reduction in the Legionella count in the cooling water after the addition of the biocide. There were not many studies conducted on the same kinds of biocides. When the same biocides were tested in more than one study, the results rarely agreed. Also, scientific statistics were rarely applied to the outcomes in many of these studies. Future Research: Biocides need more field testing in order to generate better scientific evidence as to their effectiveness against Legionella spp. in operating evaporative cooling systems.
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