Understanding the impact of environmental and operational conditions on Legionella fate, transport, and risks: Creating a pipeline for efficient outbreak investigations

Legionnaires’ disease is a severe respiratory illness caused by the bacterium Legionella pneumophila and closely related species. It is frequently associated with cooling towers, which are large mechanical systems used to remove heat from buildings and industrial facilities. Cooling towers can emit fine mists and aerosols that may contain bacteria. Once released, these aerosols can travel through the air and may expose nearby populations. However, it is not fully known how environmental conditions and system design influence infection risks. This project will combine field data, laboratory experiments, and modeling to identify and quantify the biological and environmental parameters that determine risks of disease transmission. Results from the project will help improve the management of cooling tower water quality, treatment, and operating conditions to reduce health risks. In addition, the project will provide training opportunities for students and early-career researchers in environmental engineering and public health, helping to strengthen the science and engineering workforce needed to address environmental health challenges. This project will develop a mechanistic and predictive framework to understand how environmental and operational conditions influence the persistence, aerosolization, transport, and risk of Legionella pneumophila bacteria from cooling tower systems. The research will integrate laboratory experiments, field measurements, and modeling to quantify interactions among Legionella, free-living amoeba hosts, and cooling tower water chemistry under realistic operating conditions. Controlled experiments will evaluate how factors such as nutrient levels, disinfectant residuals, pH, and desiccation influence pathogen–host dynamics in both pure cultures and pilot-scale cooling tower reactors designed to replicate operational environments. Field campaigns at full-scale cooling towers will measure aerosol generation rates and droplet size distributions using inert tracer techniques and microbial sampling to characterize pathogen-containing drift emissions. These data will inform the development of spatially resolved aerosol dispersion and risk models that incorporate pathogen persistence, environmental decay, and historical surveillance data from outbreak investigations. The resulting models will be used to hindcast known outbreaks and to generate a field-ready sampling triage framework that prioritizes high-risk downwind locations during outbreak investigations. By quantitatively linking cooling tower operational conditions with pathogen-host dynamics and aerosol transport, the project will advance fundamental understanding of opportunistic pathogen persistence in engineered water systems and improve predictive tools for microbial risk assessment and public health response. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2553834 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Kerry Hamilton | Institution: Arizona State University, SCOTTSDALE, AZ | Award Amount: $550,065 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2553834 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2553834.html