Legionella is a waterborne pathogen, that if inhaled, can cause severe illness in humans including Legionnaires’ disease and Pontiac fever. Despite growing knowledge about Legionella aerosolization and inhalation in residential, commercial, and institutional buildings and in healthcare facilities, disease outbreaks are increasing. Since the first Legionella outbreak in 1976, numerous bench, pilot, and field-scale studies have been conducted to develop strategies and guidelines for the mitigation and prevention of disease outbreaks. However, the development of a quantitative framework to predict Legionella disease outbreak in buildings has remained elusive. The overarching goal of this multi-institution collaborative project is to advance the fundamental understanding of Legionella growth in building water systems and leverage this new knowledge to develop and validate a computational model to predict potential hotspots of Legionella growth and exposure in buildings. The successful completion of this project will benefit society through the development of new fundamental knowledge and modeling tools to identify the design/operational parameters and environmental conditions of a building’s premise plumbing system that most affect the growth and persistence of Legionella. Further benefits to society will be achieved through student education and training including the mentoring of two graduate students and an undergraduate student at Arizona State University, the New York State Department of Health, and the College of New Jersey. Legionella pneumophila (L. pneumophila) is an infectious pathogen of increasing concern due to its ability to cause Legionnaires’ Disease (LD), a severe pneumonia, and the difficulty in controlling the bacteria’s persistence in drinking water systems. L. pneumophila thrives within large premise plumbing systems such as those found in hospitals. Commonly used disinfectants are not effective in eradicating L. pneumophila from premise plumbing systems. In addition, there is no validated model to predict the concentration of viable Legionella cells in a building water system. The overarching goal of this project is to develop and validate a computational model that could predict the growth and persistence of L. pneumophila within a building’s premise plumbing as a function of system design, operational parameters, and environmental conditions. The specific objectives of the research are to: (1) Use state-of-the-art, rapid sampling techniques to quantify Legionella concentrations, water quality parameters, operational parameters, and building design specifications in data-rich buildings with known Legionella problems and/or disease cases where the New York State Department of Health has ongoing partnerships; (2) Derive Legionella kinetic information over a multivariate parameter space using targeted and multifactorial experiments with a combination of parameters including biofilm conditions, disinfectant residual concentrations, temperatures, and nutrient loadings; and (3) Develop and validate a computational model (with site-specific information and updated kinetic information) to predict Legionella persistence and growth in premise plumbing systems that will inform quantitative microbial risk assessment (QMRA) models of LD outbreaks in buildings. The successful completion of this project has the potential for transformative impact through the development of new fundamental knowledge and modeling tools to support more accurate estimates of human health risks associated with LD outbreaks in buildings. To disseminate the findings of this project, the Principal Investigators (PIs) plan to conduct outreach events (including targeted workshops and conferences) to present the results of their research findings and solicit feedback from a broad audience of stakeholders including the Association of American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), the American Water Works Association (AWWA), and the US Environmental Protection Agency (EPA) premise plumbing working group. 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.