Legionnaires’ Disease

Update December 2023

The Centers for Disease Control and Prevention (CDC) recently published a report on the 2022 Legionella outbreak in Napa County that has been cited in several news articles. Health officials in collaboration with the CDC traced the Legionella outbreak to a contaminated cooling tower in the city of Napa, not a contamination of the tap water supply as media are reporting.

 Legionnaires disease is rare, but a potential outbreak must be swiftly tackled from all fronts, from sourcing to remediation. For Napa County Public Health, that response required a collaborative effort from the local, state and federal levels, including working with other public health agencies, laboratory support, timely communication with the public, and cooperation from management of potentially implicated water systems. It was through this collaboration that Napa County was able to tackle the outbreak from the environmental, epidemiological and molecular fronts to link the outbreak to the source and remediate the 2022 Legionnaires disease outbreak.

Read the CDC article here: Large Community Outbreak of Legionnaires Disease Potentially Associated with a Cooling Tower — Napa County, California, 2022 | MMWR (cdc.gov)


Legionnaires’ (LEE-juh-nares) disease is a serious type of pneumonia (lung infection) caused by Legionella (LEE-juh-nell-a) bacteria. People can get sick when they breathe in small droplets of water or accidentally inhale water containing Legionella into the lungs. Signs and symptoms of Legionnaires’ disease can include cough, muscle aches, fever, shortness of breath, headache, vomiting or diarrhea. 


Legionella is a bacterium that grows naturally in freshwater environments like, lakes and streams. When the bacteria grow in human-made water sources, such as decorative fountains cooling towers it can cause Legionnaires’ Disease. 

How it spreads

This bacteria spreads through small, aerosolized water droplets that come from a human-made water source. When someone inhales the droplets, they can become infected with Legionnaires’ Disease. This disease doesn’t spread from person to person and is treated with antibiotics.

Who is most at risk?

People over the age of 50, especially those who smoke cigarettes, or those with certain medical conditions, including weakened immune systems, chronic lung disease or other chronic health conditions, are at increased risk for Legionnaires’ disease. 

How do I prevent Legionnaires’ disease?

There are no vaccines that can prevent it. Instead, the key to preventing Legionnaires’ disease is to reduce the risk of Legionella growth and spread. Building owners and managers can do this by maintaining building water systems, hot tubs, water fountains, cooling towers, and implementing controls for Legionella. For more information, refer to the CDC website.

Napa County 2022 Legionnaires’ Disease Investigation Results 

Subtitle Table 1: Legionnaires’ Disease Outbreak Dashboard

(Click on the dashboard image above for a larger PDF version of the dashboard)

In 2022, there were 17 cases of Legionnaires’ disease and 1 death. The age range of cases was 40 to 83 years and there were 13 men and 4 women diagnosed. The symptom onset dates were: one June 25, one June 27, one July 2, one July 3, two July 8, one July 9, one July 10, two July 11, one July 12, one July 18, one July 22, one July 25, one July 28, one August 4, and one August 15.

Subtitle Table 2: Cooling Towers with a positive test for Legionella pneumophila*

LocationAddressDate SampledRemediation Completed?
Hall of Justice1125 3rd St
Napa, CA 94559
Embassy Suites1075 California Blvd 
Napa, CA 94559
Napa Superior Court1111 Third St 
Napa, CA, 94559
The Riverfront700 Main St
Napa, CA, 94559

*Legionella pneumophila is the species of Legionella bacteria most often associated with human illness

Questions or Concerns?

Please call Napa County Public Health at 707-253-4270. 

Read the Legionnaires' Disease FAQs:

More Information from the CDC:

Guidance on Building Water Systems:

This page was last updated September 2022