Legionella bacteria reside in many natural environments including rivers, lakes, and soils. These bacteria are also found in a variety of engineered systems that support biofilm growth, including drinking water supplies, cooling towers, hot tubs, fountains, and building plumbing systems and their outlets like faucets and showerheads. These water systems are often characterized by warm temperatures, stagnant water, and a lack of chemical disinfectants—conditions that promote the growth of biofilms and their associated protozoa, which are the hosts for Legionella bacteria. People are exposed to Legionella primarily through inhalation of contaminated aerosols into the respiratory system from these contaminated water systems. Those at higher risk for developing Legionnaires’ disease include the elderly, men, smokers, and the immunocomprised.
Although the Safe Drinking Water Act has been effective in reducing U.S. disease rates of enteric waterborne organisms, it has had little impact on managing Legionella in water systems and buildings. In fact, the incidence of Legionnaires’ disease has increased more than five-fold from 2000 to 2017 (see Figure 1). Facilities managers can play a major role in preventing the growth of Legionella in engineered environments like building water systems.
The reported incidence of Legionnaires’ disease in the United States has increased more than five-fold from 2000 to 2017. Many factors contribute to this increase: more people are at risk because of the aging population, increased use of immunosuppressant drugs, and higher prevalence of comorbid conditions such as diabetes and pulmonary disease. There is also a growing dependence on heating, ventilation, and cooling systems, as well as increasingly complex indoor plumbing systems in large buildings. In addition, efforts to conserve water within buildings are likely to result in an increased risk of Legionella growth due to water stagnation, temperature changes, and loss of disinfectant residual. Higher water temperatures as a result of climate change may also play a role.
Source: Adapted from Shaw et al. (2018) with 2016 and 2017 data from the National Notifiable Diseases Surveillance System.
In general, the principles to consider when determining whether a building water system presents a potential risk as a Legionella source and requires control are:
Design and commissioning of a large building is a key opportunity to ensure that Legionella control is prioritized, including the appropriate design and implementation of hot and cold water systems and heating, ventilation, and air conditioning (HVAC) features. Furthermore, they should be configured to facilitate the collection of water for Legionella monitoring and for the implementation of maintenance and remediation (such as sampling and injection ports on hot water lines). Hospitals or other buildings where sensitive populations are housed should be designed with the ability to conduct remediation in the case of contamination by Legionella or other pathogens. Unfortunately, the majority of existing large buildings were not designed in this manner and present numerous complex challenges with Legionella control.
It is clear from research and practice that, in most situations, “zero” is not an achievable target for evaluating whether Legionella has effectively been controlled, for several reasons. Some level of Legionella is common in drinking water systems in the absence of an outbreak. The following are the fundamental factors that building managers must consider in controlling Legionella.
The report recommends that all public buildings have a Water Management Plan for Legionella. Today, only hospitals and healthcare facilities in New York State, those in the Veterans Health Administration network, and those that receive Medicaid and Medicare funding are required to have such plans.
There are many potential locations where Legionella may be present in a large building that should be targeted for sampling. Examples are as follows:
Once the locations that will provide a good indication of system performance are identified, the interval for sampling can be determined. In cases where initial testing indicated there was no presence of Legionella anywhere in a facility, and the building use composition indicated no risk of exposure to building occupants, sampling may be done once every 6 months or even once per year. The sampling interval is also driven by the building’s risk tolerance. A hospital with a large immunocompromised patient population and zero tolerance for Legionella may opt for more frequent sampling. In either case, the sampling strategy is dictated by risk and the Water Management Plan parameters.
In order to quantify the relationship between levels of Legionella bacteria and outbreaks of Legionnaires’ disease, the report’s authoring committee reviewed dozens of studies on the occurrence of Legionella in various building types during outbreaks and routine monitoring. The committee found that a Legionella concentration of 5 × 104 colony forming units per liter should be considered an “action level” (i.e., a concentration high enough to warrant serious concern and trigger remediation in a building water system). A lower action level may be necessary to protect those at higher risk for Legionnaires’ disease such as hospital patients, particularly those in intensive care, cancer, and solid-organ transplant units.
The role of liability in the control and prevention of Legionnaires’ disease has been mixed in the United States. Multi-million-dollar lawsuits are not uncommon for Legionnaires’ disease when the environmental source is tracked to a large building or other entity where the owner and/or other persons are responsible for the safety of those served by an implicated water system. Manslaughter charges have been filed on rare occasions. To protect their clients, some lawyers have advocated that the water facilities considered at risk (e.g., hotels, hospitals) test their water for Legionella as part of a Water Management Plan, while others have advocated that it is better not to test because the results could potentially be used against their client. This latter argument will probably not become entrenched as testing becomes more common, and “not knowing” may hurt rather than help the defense. The growing number of litigants and the large size of settlements may result in the insurance industry pushing many clients with water systems serving the public into improving their prevention programs for Legionnaires’ disease. As Legionella awareness grows, monitoring and protecting systems will most likely be an important step to remain up to date in maintenance management, protect building occupants, and avoid lawsuits.