Legionella Treatment: Approaches to Disinfection


Prompted by the abundance of news coverage around COVID-19, a public radio station in Illinois recently broadcast a story about another threat to public health — one that’s often overlooked: 569 cases of Legionnaires’ Disease (Legionellosis) were reported in the state of Illinois alone in 2019. 43 of those patients died.

Nationwide, there were almost 10,000 cases of Legionnaires’ disease confirmed by health departments in 2018, but it is suspected that many other incidences of Legionella infection went unreported. In fact, some experts estimate that between 70,000 and 100,000 individuals may be affected by Legionellosis in the United States each year. Legionellosis is often misdiagnosed and reported as influenza, pneumonia, or a similar malady. 

A CDC fact sheet puts the mortality rate due to Legionella infection at about 15 percent. Other sources say 10 percent. The current estimated mortality rate for coronavirus (SARS-CoV-2) is 3.4 percent, according to the World Health Organization (WHO). That means Legionella victims are three to four times more likely to die from Legionella-related illness than patients who acquire COVID19.

This article is not meant to downplay the seriousness of COVID-19. Rather, the hope is to help increase awareness about Legionnaires’ disease as an important public health issue. It is a dangerous and persistent public health problem that has increasingly plagued hospitals, hotels, and other facilities for years. 

Below, you’ll find more information about Legionnaires’ disease, including information on methods for both “shock treatment” and ongoing Legionella control. You’ll also find a review of the considerations FACS suggests for developing an effective Legionella management strategy.

Legionnaires' Disease on the Rise Graph

Credit: Centers for Disease Control and Prevention.


Legionnaires’ Disease is Still a Very Real Threat to Public Health

A 2002 paper published by the American Society for Microbiology issued this warning concerning the lack of attention given to the disease:

Legionnaires’ disease has a false but enduring status as an exotic plague. In reality, this disease is a common form of severe pneumonia, but these infections are infrequently diagnosed. Failure to diagnose Legionnaires’ disease is largely due to a lack of clinical awareness. In addition, legionellae, the bacteria that cause this disease, are fastidious and not easily detected.

A State Hygienic Laboratory report from the University of Iowa noted the steady increase in Legionnaires’ disease cases and said this:

The Centers for Disease Control and Prevention reported that from 2000 to 2017, the number of confirmed cases increased more than fivefold, but notes the number may be much larger because legionellosis is often missed as a diagnosis.

Despite a concerted public and private effort to control the spread of Legionella bacteria to humans, outbreaks continue to appear. With the 2020’s barely underway, numerous cases of Legionnaires’ disease have already been reported. A quick search brings up stories of the disease afflicting people in Illinois, Ohio, Florida, and Pennsylvania. Nor is Legionella an American phenomenon. The news also reports cases in China, Australia, and around the globe.

In Ireland, an article titled “Legionnaires’ disease left guest at five-star hotel fighting for life,” announced the financial settlement of a Legionella infection from 2015. Think of the damage done to the reputation of that property by the ongoing litigation. “Little did she know when she went for a break at the hotel,” reads the article, “that it would almost claim [her] life.”

Legionnaires’ disease is still a very real threat to public health. Fortunately, the bacteria isn’t generally transmitted human-to-human by coughs and sneezes, but by droplets of water that are inhaled from aerated systems. Common sources of Legionella-infected water include centralized air conditioning, showers, hot tubs, water features, and such.

Two Types of Treatment to Control and Prevent Legionella Concentrations in Water Systems

In cases where Legionella amplification has been confirmed, or when conditions conducive to Legionella growth are present, “shock treatments” are usually the best option. Shock treatment typically involves the short-term application of a disinfectant at high concentrations. It is flushed through the system and held for a specific contact time. 

Ongoing, or “supplemental” disinfection, may be necessary when shock treatment is not successful in eradicating Legionella or when systemic contamination with well-established biofilm is suspected. Supplemental disinfection involves the installation of a permanent or semi-permanent disinfection system that applies continuous long-term disinfectant dosing over time.

There are a variety of disinfectants available for use in both shock and supplemental treatment. Examples include chlorine, chlorine dioxide, monochloramine, mixed oxidants, copper-silver ionization, ultraviolet light, and ozone. 

The selection of an appropriate choice or combination of choices for disinfection should be made by a multidisciplinary water management team under the guidance of a qualified Legionella professional. Many times, outbreaks occur when choices about disinfectants and application methods are made by maintenance staff who don’t have sufficient knowledge about Legionella control.

The selection of an appropriate disinfection method should be based on a thorough risk assessment of the building and its water system. There is no one-size-fits-all solution for every building and every condition. Each situation must be evaluated as a unique environment with its own special areas of concern. 

For instance, here are some of the factors that affect selection of an effective disinfectant:

  • Disinfectant strength
  • Disinfectant concentration
  • Contact time required
  • Ability of the disinfectant to penetrate biofilm
  • Permits or other regulatory requirements that must be met in order to apply the disinfectant
  • Plans for renovation or repairs in the facility
  • Sensitivity of building occupants
  • Design of the water system
  • Water usage patterns
  • Stagnation or flow issues 
  • Cost of treatment
  • Ease of installation
  • Timeline for application

The COVID-19 crisis signals special considerations for building maintenance engineers. Many facilities have sat dormant or experienced a major downward shift in usage. When those buildings are reopened, the risk of Legionella growth due to stagnant conditions within the HVAC system is greater than before. 

An experienced Legionella advisor can often save the facility considerable time and money. More importantly, the right approach to Legionella prevention and control protects the lives of all who come in contact with building water systems.

Why it's important to consult qualified Legionella professional infographic

Legionella Treatment and Management Strategies

Legionella contamination can be difficult to eradicate, especially when stubborn biofilms have been established over time. Whenever disinfection is utilized as a control method, it is important that verification and validation monitoring be performed to ensure efficacy. 

Concentrations must be regularly monitored during the disinfection process to ensure targets are reached and maintained. Depending on the disinfectant and method applied, disinfection byproduct monitoring may also be required to comply with drinking water standards. 

Flushing may be needed to ensure the disinfectant reaches areas where water may be stagnant. Legionella sampling should be performed after shock disinfection has been completed or secondary disinfection is established. Sampling confirms the reduction and continued control of Legionella bacteria.

FACS encourages facility managers to take a proactive approach by establishing and implementing a water management plan that sets forth clear and simple-to-follow instructions for the control of Legionella

Examples of sections that should be included in that plan are the identification of Legionella hot spots, monitoring the system for Legionella, treating for control, what to do when concentrations of Legionella are detected, when to implement  treatments, and how to manage public relations for Legionella-related issues. 

Most facilities don’t have a qualified Legionella expert on staff, however. And even those that do feel their strategy is appropriate enjoy the additional layer of protection that comes from having a third-party review of the water management plan and an inspection of the system to check for existing or potential problems. Legionella outbreak situations can be deadly, stressful, and costly. They’re a nightmare no facility or company should ever face.

Don’t take chances with Legionella, and don’t get blindsided by an outbreak. If your building or mobile unit uses water, it’s a potential spot for a Legionella growth explosion. 

For example, a 2019 outbreak of Legionnaires’ disease at the Mountain State Fair in North Carolina infected 136 fair attendees, hospitalized 97, and killed four. An improperly sanitized hot tub display is the suspected source. Victims didn’t have to soak in the hot tubs. It was only necessary for them to walk by. Imagine what can happen when a cooling tower that serves an entire building is contaminated with Legionella.

How to Find a Legionella Control Expert

Here’s how to get more information or schedule an on-site visit by a Legionella specialist: Call FACS at (888) 711-9998. The quicker you make that call, the sooner potential exposures in your facility can be identified. 

If you already face a Legionella-related problem, FACS will help you communicate with public health officials and work with your team to quickly identify appropriate remediation measures to bring the water system back online again so your building can return to normal operation as soon as possible. 

Call FACS at (888) 711-9998 or use our online contact form to set up a conversation about Legionella identification, treatment, and disinfection.