Office of Research and Development Publications

Preventing Disease from Legionella is a Shared Responsibility

Citation:

Bourdon, L., J. Liggett, F. Sidari, AND S. Triantafyllidou. Preventing Disease from Legionella is a Shared Responsibility. OPFLOW. American Water Works Association, Denver, CO, 45(2):10-13, (2019). https://doi.org/10.1002/opfl.1141

Impact/Purpose:

This article is a high-level, non peer-reviewed introduction to Legionella bacteria. It is intended for drinking water operators who subscribe to AWWA's Opflow magazine. It contains background information on what Legionella Bacteria are, an overview to the pathway for human exposure to Legionella in building plumbing systems, and a short introduction to water management programs. It is essentially a brief literature review (no EPA data).

Description:

For decades, the focus of drinking water providers has been on fecal pathogens like E. coli, Giardia, and Cryptosporidium. In recent years, drinking water professionals and building operators have begun to recognize the importance of so-called opportunistic pathogens like Legionella. Legionella is a genus of bacteria that is found naturally in soil, surface and ground water. Legionella is currently the number one cause of waterborne disease outbreaks in the US. Three factors play a role in the development of disease from Legionella: 1) favorable conditions in building water systems for a pathogenic species of Legionella to proliferate, 2) transmission of Legionella from the water to the lungs through aspiration or aerosolization, and 3) susceptibility of the exposed individual. Legionella can survive in a wide range of water temperatures, with an optimal growth range between 77⁰ and 108⁰ F (25⁰ – 42⁰ C). These optimum temperatures are not often found in drinking water distribution systems but can be common in building water systems, specifically hot water and non-potable water systems, where Legionella can grow and become a persistent problem. Low disinfectant residuals, typically caused by high water age, sediment, or corrosion products, can further contribute to favorable growth conditions. Legionella are also parasites to some species of protozoa. While living and reproducing inside protozoa, Legionella are provided an extra level of protection from disinfectants. If a pathogenic species of Legionella colonizes a building water system, it must be transmitted to the lungs of a susceptible person for disease to occur. Common sources of transmission through aerosols or aspiration include shower heads, cooling towers, faucets, water-based humidifiers, hot tubs, decorative fountains, medical devices, misters, and ice machines. Susceptible individuals are typically elderly, smokers, male, or immunocompromised, although studies have found that approximately 25% of cases may not have any of these typical risk factors. Controlling Legionella growth is especially important in hospitals and long-term care facilities because they house susceptible populations. Preventing disease from Legionella is a shared responsibility between water providers and building/property owners. Water providers have a responsibility to maintain a disinfection residual to all customers and implement best management practices for storage and distribution systems. Building owners are responsible for managing their building water systems to minimize the risk for Legionella. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has developed Standard 188. ASHRAE Standard 188 requires that property owners evaluate their building water systems to determine if there is a need to implement a water management program. A water management program consists of a plan to identify, monitor, control, validate, and document the actions taken to control the growth and spread of Legionella in building water systems.