The accuracy and efficacy of Legionella testing is affected by a variety of factors that increase measurement uncertainty. Such factors include interference from non-Legionella organisms, subjective interpretation of test results, and differential performance of agar media, among others. Examples of these effects are discussed in relation to strategies for minimizing uncertainty. A culture method based on a most probable number (MPN) technique for quantification can provide an alternate approach to reducing measurement uncertainty. A comparison of a MPN method with conventional agar plate methods is presented with a specific focus on the challenges associated with testing nonpotable water from cooling towers and related sources.
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