Legionella Outbreak Linked to Kaiser Santa Clara Infects 18 in California

Eighteen cases of Legionella have been linked to an outbreak at Kaiser Santa Clara Medical Center in Santa Clara, CA.¹

Santa Clara County public health officials have released a health alert in the South Bay as they partner with the Kaiser facility to trace the source of the bacteria. It was first detected during a routine internal operations review at the facility. However, officials have yet to affirm who was infected and if they were staff, patients, or visitors.^2,3 Legionella is a bacterium that causes Legionnaires’ disease, a serious type of pneumonia. It can also cause Pontiac fever, a milder illness associated with fever, muscle aches, and headaches.⁴

“While we work to determine the source, out of an abundance of caution, we have implemented additional water treatment measures and have taken preventive measures to ensure the safety of all patients, employees, and visitors,” a representative of Kaiser Permanente said in a statement.³

Legionnaires’ disease and Pontiac fever are contracted through inhaling mist containing the bacteria. Another way it is contracted is through drinking contaminated water; although significantly less common, it is still feasible.⁴ Yet, it is unlikely for healthy people to contract legionnaires’ disease or Pontiac fever from the bacteria. Instead, older individuals, as well as those with preexisting conditions or specific lifestyles, are at a higher risk of contracting an infection.

Who Is Most at Risk for Legionnaires’ Disease?

Individuals more susceptible to infection are those who are current or former smokers, over the age of 50, or those with specific health issues like cancer, chronic lung disease, diabetes, kidney or liver failure, or a weak immune system.

Legionella is treated with specific antibiotics, which remedy most cases. Although it is unlikely a healthy person will get sick from the bacteria, the earlier they are treated, the higher the likelihood of recovery. However, about 10% of those who have contracted Legionnaires’ disease are at risk for lung failure and death, and this risk increases to 25% if the disease was contracted during a stay at a health care facility.

“Public Health is working with the facility to ensure anyone with symptoms is appropriately treated and that the facility is taking necessary steps to prevent people from getting sick,” the spokesperson from the Santa Clara County Public Health Department said in a statement to the Santa Cruz Sentinel.²

How Legionella Spreads Through Hospital Water Systems

The bacteria naturally occur in lakes, rivers, and man-made water systems, meaning they can grow and spread in showerheads, sink faucets, decorative fountains, hot tubs, and large, complex plumbing systems.³ The general amount of Legionella in freshwater environments is not likely to lead to disease; it only begins to pose a health risk once it gets into man-made infrastructures.⁴

Certain conditions allow the Legionella bacterium to grow and spread, like in a biofilm. Biofilm is a collection of germs, such as bacteria, fungi, or amoeba, that create a slimy, glue-like substance, allowing bacteria to stick to surfaces like the inside of a water pipe.⁵

Other conditions that can fuel the spread of Legionella are environments with temperatures between 77 and 113 degrees Fahrenheit, poorly disinfected surfaces or areas, or slow or stagnant water movement.⁴

To prevent germs and bacteria like Legionella from accumulating in your home, the CDC recommends flushing unused faucets or showerheads by running cold water for at least 2 minutes, followed by hot water. The government entity also emphasizes that unwarranted drops in water pressure should be treated with the same precaution.⁵

Bacteria can also spread through mist from humidifiers of continuous positive airway pressure. Because of this, it is important to regularly clean the mask, humidifier, and tubing.

“While we work to determine the source, out of an abundance of caution, on Monday we concluded additional water treatment measures and preventive measures to ensure the safety of all patients, employees, and visitors,” the Santa Clara County Public Health Department spokesperson wrote.²

References

1. 18 people sick as officials probe legionella outbreak at Kaiser Santa Clara. ABC7 San Francisco. May 7, 2026. Accessed May 12, 2026. https://abc7news.com/post/18-people-sick-officials-probe-legionella-outbreak-kaiser-santa-clara

2. Stringer G. 18 cases of legionella, waterborne bacteria, found at Kaiser Santa Clara Hospital. Santa Cruz Sentinel. May 9, 2026. Accessed May 12, 2026. https://www.santacruzsentinel.com/2026/05/09/18-cases-of-legionella-water-borne-bacteria-found-at-kaiser-hospital/

3. Bradley I. Public health officials confirm 18 legionella infections connected to Kaiser Permanente Santa Clara. KTVU FOX 2 San Francisco. May 6, 2026. Accessed May 12, 2026. https://www.ktvu.com/news/legionella-bacteria-detected-kaiser-permanente-santa-clara

4. About legionnaires’ disease. Centers for Disease Control and Prevention. August 6, 2025. Accessed May 12, 2026. https://www.cdc.gov/legionella/about/index.html

5. Preventing waterborne germs at home. Centers for Disease Control and Prevention. March 15, 2024. Accessed May 12, 2026. https://www.cdc.gov/drinking-water/prevention/preventing-waterborne-germs-at-home