There is still much to learn about the bacterium Legionella pneumophila and some of the other members of the genus Legionella that can cause Legionnaires' disease. But we already know for certain that parts of building water systems like cooling towers, hot tubs and hot and cold potable water systems can provide the conditions needed for the bacteria to grow or even thrive. Big populations of Legionella pneumophila that grow in inadequately managed building water systems pose an increased risk of Legionnaires' disease for the building occupants, visitors and staff. Understanding and managing this risk will take a partnership between drinking water suppliers (public water systems), building owners and operators and public health authorities.

Public Water Systems

The panels below describe the sequence of events that result in exposures to Legionella bacteria from potable water systems. Because Legionella are environmental bacteria (bacteria that can grow in the environment without hosts) and because Legionella is suited for survival in treated drinking water, studies have shown that Legionella bacteria are often present in drinking water supplies, though usually at very low numbers. As a partner in managing Legionnaires' disease risk, public water systems can treat and manage their water to reduce the likelihood that Legionella bacteria are present at high numbers, but in most cases they cannot eradicate them.

Building Owners and Building Water System Operators

If water with low numbers of Legionella bacteria get into a building water system, conditions can be much better for the bacteria to grow to numbers that make infection more likely. Water in building water systems is no longer under the control of water supplier; it is the responsibility of the building owner and (for large buildings) the staff who maintain and operate the water systems. So, building owners and water system operators are the second partners in Legionnaires' Disease risk management. There are many actions that can reduce the likelihood the Legionella bacteria grow to risky populations and the best approach for making sure the right actions are taken is to develop and implement a Water Management Program. The US Centers for Disease Control and Prevention water management program toolkit ( Toolkit: Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings ) is a good resource for developing and sustaining a water management program.

The Public Health Community

The third critical partner in Legionnaires' disease risk management is the public health community. Public health officials track Legionnaires' disease and epidemiologists research Legionnaires' disease cases and outbreaks to determine the source. The public health community also has a limited degree of oversight for water systems of health care facilities and, in some communities, has programs for managing Legionnaires' disease risk from cooling towers. Cooling towers are separate from building potable water systems and have been identfied as the source of pathogens in some large recent outbreaks.

An important element of Legionella risk management in both public water systems and building water systems is monitoring for L. pneumophila. Monitoring is under consideration as part of EPA's upcoming revisions to Microbial and Disinfection Byproduct Rules and is a key component of building water management plans. The water community is currently debating where, when and how L. pneumophila should be monitored and how samples should be assayed. ESPRI chief scientist Dr. Jennifer Clancy has recently published a paper in AWWA Water Science on performance of the new Legiolert culture method for assaying water samples. In general, field data from sampling campaigns in numerous buildings showed Legiolert to be more sensitive and accurate than culturing via BYCE. The abstract of the paper may be found here.