Resilient water systems: A multiscale strategy to control Legionella in cooling towers

Cooling towers (CTs) are essential infrastructure components but often serve as overlooked reservoirs for Legionella pneumophila, the bacteria responsible for Legionnaires’ disease. Their warm, nutrient-dense, stagnant environment fosters the survival, growth, and aerosol transmission of Legionella. This review covers current knowledge on the biology, adaptability, and spread of Legionella in water systems, focusing on CTs as control points. Detection methods (e.g., culture, qPCR, and rapid diagnostics) were evaluated and highlight the importance of a layered surveillance approach that balances sensitivity, speed, and regulation. Additionally, chemical methods were discussed, emphasizing oxidizing and non-oxidizing biocides, and supporting dual-biocide strategies to ensure long-lasting control of both free-floating and biofilm bacteria. Furthermore, design improvements, routine maintenance, and water quality monitoring are vital for controlling Legionella. A global comparison reveals gaps, especially in high-risk, under-regulated regions. Expanding enforceable, context-specific guidelines, boosting capacity building, promoting public awareness, and implementing integrated surveillance are crucial. Climate change and urbanization increase dependence on cooling systems, making international cooperation vital to ensure Legionella-free water systems.