18 Legionella infections confirmed at Bay Area Kaiser hospital

Kaiser Permanente confirmed late Wednesday that 18 people were infected with Legionella at its Santa Clara medical center, where officials are still trying to determine the source of the contamination.

The health system said it found the infections during routine monitoring. The hospital and its nearby medical office building remain open and are operating normally.

Kaiser did not say whether the 18 infected people were patients, employees or visitors. It also did not say whether anyone had been hospitalized.

"The source of the contamination is unclear at this time," a Kaiser Permanente spokesperson said in a statement. "Per the Santa Clara County Public Health Department, there is low risk to the community."

Legionella bacteria are found naturally in water. They can cause Legionnaires' disease, a serious type of pneumonia, and Pontiac fever, a milder illness, according to public health officials.

The bacteria do not spread from person to person. People usually get sick by breathing in mist from contaminated water, Kaiser said - not by standing near someone who was exposed or by using water for routine hygiene or other everyday purposes. Kaiser said masks are not needed for people who may have been exposed or for those around them.

Human-made water systems can allow the bacteria to grow and spread, including showerheads, sink faucets, hot tubs, decorative fountains, cooling towers and large plumbing systems, according to public health guidance.

Kaiser said it is working with local and state public health officials to investigate the cases.

"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," Kaiser Permanente said.

The spokesperson said the medical center remains safe for patients and visitors.

"We take this matter seriously and are committed to maintaining a safe environment for all patients, members, visitors, and staff," the statement said.

People at higher risk of serious illness include adults 50 and older, current and former smokers, people with chronic lung disease, diabetes or cancer, and people with weakened immune systems, according to public health officials. Legionnaires' disease can be treated with antibiotics.

Symptoms can include fever, cough, shortness of breath, muscle aches, headache, nausea or diarrhea. People with symptoms or concerns about possible exposure should contact a health care provider.

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This story was originally published May 7, 2026 at 10:32 AM.