Rapid Testing and Interventions to Control Legionella Proliferation following a Legionnaires’ Disease Outbreak Associated with Cooling Towers

Abstract

Most literature to date on the use of rapid <i>Legionella</i> tests have compared different sampling and analytical techniques, with few studies on real-world experiences using such methods. Rapid tests offer a significantly shorter feedback loop on the effectiveness of the controls. This study involved a complex of five factories, three of which had a history of <i>Legionella</i> contamination in their cooling water distribution system. Multiple sampling locations were utilised to take monthly water samples over 39 months to analyse for <i>Legionella</i> by both culture and quantitative polymerase chain reaction (qPCR). Routine monitoring gave no positive <i>Legionella</i> results by culture (<i>n</i> = 330); however, samples were frequently (68%) positive by qPCR for <i>Legionella</i> spp. (<i>n</i> = 1564). <i>Legionella</i> spp. qPCR assay was thus found to be a good indicator of cooling tower system health and suitable as a routine monitoring tool. An in-house qPCR limit of 5000 genomic units (GU)/L <i>Legionella</i> spp. was established to trigger investigation and remedial action. This approach facilitated swift remedial action to prevent <i>Legionella</i> proliferation to levels that may represent a public health risk. Cooling tower operators may have to set their own action levels for their own systems; however, in this study, 5000 GU/L was deemed appropriate and pragmatic.