Across the United States, reported cases of Legionnaires’ (LEE-juh-nares) disease have been increasing since the early 2000’s, including in King County. In 2025, there were 33 cases of Legionella infections among King County residents compared to 8 cases in 2005. But there is good news: Legionnaire’s disease is preventable!
Dr. BreeAnna Dell, a program manager for Zoonotic & Emerging Infections with Public Health – Seattle & King County, has seen recent infections that may have come from hot tubs while traveling or humidifiers in peoples’ homes. We sat down with Dr. Bree to learn how she and her team try and uncover the sources of these infections and ways to prevent this disease.
What is Legionnaires’ disease?
Legionnaires’ disease is a serious type of pneumonia caused by a kind of bacteria called Legionella. Like other types of lung infections, symptoms include cough, fever, headaches, muscle aches, and difficulty breathing.
How do people get sick?
Typically, legionnaires’ disease doesn’t spread from person to person. Instead, people can get sick by breathing in mist (small droplets of water) containing Legionella. These bacteria occur naturally in the environment but become a risk when they are concentrated in places like plumbing systems, showerheads, hot tubs, and cooling towers. Warm water and the formation of hard-to-clean blobs of bacteria called biofilms can help the bacteria grow and survive. Typically, Legionella comes from water systems such as:
- Showerheads
- Sink faucets
- Hot tubs
- Fountains
- Cooling towers
How have King County residents gotten sick?
In one recent King County investigation, a person explained that they were on a cruise and had been around mist from hot tubs and fountains. In a different case, we discovered that the sick person’s home plumbing was old and had never been updated. Knowing these bits of information helps us to identify sources of infections and prevent future illnesses.
Who is at risk and how can I protect myself from Legionnaires’ disease?
The good news is that most healthy people that are exposed don’t get sick. People at higher risk of infection include those who:
- Are 50 or older
- Currently or have previously smoked
- People with chronic lung disease
- Have specific health conditions or weakened immune systems
People should check with their doctor quickly if they have flu-like symptoms or difficulty breathing, especially people who are over 50, current or former smokers, or have weakened immune systems. Early detection and treatment can minimize the severity of Legionnaires’ disease and other pneumonias.
It is also important to stay up to date on vaccines for illnesses like flu and pneumonia – diseases which make it hard for the lungs to fight off Legionella bacteria.
Additionally, King County residents can take precautions in their home and while travelling. At home, residents can:
- Keep hot water heater temperatures between 120F to 140F
- Flush hot water heaters annually
- Regularly check and maintain chlorine levels in pools and hot tubs
- Drain garden hoses and do not leave water-filled hoses in the sun
- Clean and replace water filters around the home, including whole-house and point of use filters (such as sinks and refrigerators)
- Properly clean home-use machines such as CPAPs, humidifiers, and other mist-generating devices. Use distilled water (or boiled water after it is cooled back to room temperature)
- Follow the manufacturers’ recommendations for the cleaning and maintenance of all of these water sources
While traveling, residents can:
- Run the shower and faucets on hot for a few minutes before showering or using sinks. This may reduce the risk by clearing out some bacteria.
- Be aware of local health advisories and follow any recommendations.
Why are more people getting sick?
There are many factors contributing to increasing numbers of Legionnaires’ disease cases, especially in cities with more buildings and infrastructure. Climate change and rising temperatures is one example. To help with the heat, newer commercial buildings like schools, hospitals, and industrial facilities are using cooling towers to help cool the building. These towers use water that can be released as mist into the air and are a known source of Legionella infections.
What does King County do to protect residents from Legionella?
Cases of Legionnaires’ disease are reportable in the state of Washington, which means healthcare providers notify Public Health about all cases that they see. Public Health then investigates these cases, with the goals of identifying sources of illness, detecting outbreaks, and preventing more people from getting sick. In our investigations, disease experts review diagnostic tests and gather information from sick people about recent activities that might have exposed them. This could range from details about a recent vacation to whether they use a nebulizer at home. We ask questions about:
- Travel history
- Activities around human-made water sources
- Occupational exposures
- Time spent around certain types of buildings or facilities
- Health history for understanding risk and symptoms
Public Health might request more advanced testing, called sequencing, if we identify common risk factors between cases. Sequencing allows Public Health to know how related Legionella bacteria are to each other and can help us better understand if people were infected from the same source.
Find out more about Legionnaires’ disease:
Washington State Department of Health – Legionnaires’ Disease
Originally Published 4/2/2026