The National Academies of Sciences, Engineering, and Medicine will undertake a project on the management of Legionella in water systems. Legionella is a bacterium found in drinking water distribution systems, premise plumbing, hot tubs, hot water heaters, cooling towers, fountains, and other building water systems. At high enough concentrations and when inhaled, Legionella can cause legionellosis, which includes Legionnaires’ disease and Pontiac fever. An ad hoc committee of the Academies will review the state of science with respect to Legionella contamination of water systems and issue a report on the following:

Ecology and Diagnosis: Describe the microbial ecology of water supplies (from the source to the tap and within built systems) as it relates to Legionella. What species and strains of Legionella are of most concern and can their diagnosis be improved (in terms of increased specificity, simplicity, and speed)?

Transmission via Water Systems: What are the primary sources and routes of human exposure to Legionella? What features/characteristics of water systems make them more or less likely to support growth of Legionella?

Quantification: Considering surveillance data, case studies of outbreaks, hospital data, other routine testing of water systems, what is known about the concentration of Legionella in water systems and the prevalence of legionellosis over the last 20 years? How uncertain are these estimates and what can be done to reduce this uncertainty? How can quantitative risk assessment be improved?

Prevention and Control: What are the most effective strategies for preventing and controlling Legionella amplification in water systems? What are the best methods to prevent exposure to Legionella, especi-ally in at risk populations? Is there a minimum level of contamination required to cause disease? What are the benefits, risks, gaps in implementation, and barriers to uptake of Legionella control programs?

Policy and Training Issues: What policies, regulations, codes, or guidelines affect the incidence, control, quantification, and prevention of legionellosis? How might they be built upon to better protect the public? How can Legionella control be best balanced with other water priorities?

Research: For the above issues, what additional information gaps exist and what knowledge must be gathered to fill these gaps?