Why Legionnaires' Disease Cases Continue to Rise Despite Current Prevention Strategies

Despite decades of research into Legionella and growing awareness of water management programs, cases of Legionnaires' disease continue to climb in the US. According to Hung Cheung, MD, board member and medical advisor to the Alliance to Prevent Legionnaires' Disease (ALPD), the continued increase suggests it is time to rethink current prevention strategies.

"There’s a 5-and-a-half-fold increase in Legionnaires' disease since the year 2000," Cheung said. "If we know the source and our approach is appropriate to address it, then we should have it well controlled, and it is not."

Rather than focusing primarily on building-level responses after cases occur, Cheung believes infection prevention efforts should move closer to the source of exposure by improving water quality throughout municipal distribution systems.

Looking Upstream

Cheung compared the current approach to the history of cholera control.

Referencing physician John Snow, often considered the father of modern epidemiology, Cheung explained that Snow did not attempt to disinfect every individual building affected during London's cholera outbreaks. Instead, he identified the contaminated water source and interrupted transmission at its origin.

"So that's why we believe...you should tackle things as far upstream or proximal to the source as possible," Cheung said. "By the time you get down to homes and buildings, it's a lot more work. Ensuring good quality water coming from the utilities and the distribution system is the best return on the investment."

The Alliance's legislative recommendations include stronger communication between water utilities and downstream facilities during planned or unplanned disruptions.

"If there's a way for hospitals and nursing homes to manage it, filter out all the material that's now being thrown downstream, then we can prevent a lot of illnesses and deaths," he said.

Water Disruptions Can Increase Risk

Cheung noted that routine utility activities, including water source changes, pipe repairs, chlorine burns, and severe weather events, can disturb biofilms within water systems.

"When biofilm is lifted off, it sends bacteria downstream," he explained. "Not just Legionella, but other bacteria can live there as well."

For hospitals and long-term care facilities, awareness of these events could allow infection prevention teams to implement temporary mitigation strategies before patients are exposed.

Beyond Outbreak Investigations

Cheung also questioned the current emphasis on investigating only outbreak-associated cases.

He noted that outbreaks account for only a small percentage of Legionnaires' disease nationally.

"If you only investigate some of the outbreak cases, you're developing an approach for up to 4% of the cases," he said. "Now you have 96% that are nonoutbreak cases, and you're assuming they behave similarly. They may or they may not."

He compared the situation to survey methodology.

"If only 4% of people respond to a survey, you wouldn't automatically assume they represent everyone else without looking at the non-responders," Cheung said.

According to Cheung, understanding sporadic cases may reveal transmission patterns that current investigations miss.

Prevention Before Illness

Cheung described ALPD's philosophy as one centered on primary prevention rather than reacting after the disease has already occurred.

"The problem with waiting until an outbreak and then investigating a building is that it's late in the game," he said.

Instead, he advocates improving source water quality, educating health care providers and the public, and preparing facilities for water disruption events before illnesses develop.

Education also plays a critical role in clinical recognition.

"If there's a major storm or another water disruption and you see a pneumonia patient, you should have a high index of suspicion that it may be Legionnaires'," Cheung said. "Legionnaires' presents like other pneumonias, but there's an antibiotic of choice. Appropriate treatment requires that you recognize it."

He also encouraged routine maintenance practices that reduce bacterial habitats, including flushing and draining residential hot water tanks to remove accumulated sediment.

A Public Health Perspective

For infection preventionists, Cheung's recommendations extend beyond individual facility water management plans. He believes stronger partnerships among water utilities, public health agencies, hospitals, and long-term care facilities could help reduce exposure before contamination reaches vulnerable patients.

"We're talking about prevention," Cheung said. "A lot of prevention-type approaches to tackle this issue."