Kaiser Permanente is still trying to determine the source of bacteria responsible for 19 recent cases of Legionella infection identified at a hospital in the San Francisco Bay Area.
The 19 infections were linked to Kaiser’s medical center in Santa Clara. Most of those who fell sick are recovering at home, Kaiser said in a recent statement.
The bacteria were identified through “robust routine internal monitoring processes,” according to Kaiser.
“Our medical center is a safe place to visit and receive care,” the health system said.
Kaiser did not specify how ill those infected are, nor did they say specifically how the bacteria were detected.
Infection can occur when Legionella — which appears naturally in environments such as lakes and streams — gets into building water systems and people breathe in mist containing the bacteria, according to the U.S. Centers for Disease Control and Prevention. The bacteria grow best in warm temperatures, between 77 and 113 degrees.
The disease does not spread from person to person.
The most severe form of Legionella bacteria infection leads to Legionnaires’ disease, a serious and potentially deadly type of pneumonia, the CDC says. Legionnaires is treatable with antibiotics, but early treatment improves the odds of recovery.
A milder form of Legionella infection called Pontiac fever can also cause aches and headaches.
Legionella can grow and spread in devices such as hot tubs, cooling towers, hot water tanks, complex plumbing systems, showerheads, sink faucets and decorative fountains, according to the California Department of Public Health. Most people who are exposed to Legionella don’t get sick, but the bacteria can cause serious infections in some cases.
“While we work to determine the source, out of an abundance of caution, last week we concluded additional water treatment measures and preventive measures to ensure the safety of all patients, employees, and visitors,” Kaiser said in its statement. “As a result of mitigation efforts, our hospital and medical office building continue to operate normally. “
About 1 in 10 people who get Legionnaires’ disease die due to complications from their illness, the CDC said. For those who contract it during a stay at a healthcare facility, about 1 of every 4 are expected to die.
Legionnaires’ disease was discovered in 1976 after a major outbreak affecting attendees of a convention of the American Legion in Philadelphia, according to the CDC. The outbreak led to 221 illnesses across Pennsylvania, and 34 deaths.
Investigators eventually suspected that the bacteria were airborne and had infected people after contaminating the air conditioning system at the convention hotel.
“Since 1976, air conditioning systems changed and agencies around the world have more stringent cleaning and hygiene standards for cooling towers and large-scale air-conditioning systems,” the CDC says.
Other ways facility managers can reduce the risk of Legionella include disinfecting cooling towers and water systems, establishing a water management program and routinely performing water system maintenance.
Legionnaires’ disease has been on the rise since the early 2000s, according to the CDC.
In 2024, seven cases of Legionnaires’ were reported in the northwestern corner of the city of Westminster, according to the Orange County Health Care Agency. No source was ever found for that outbreak, “as is so often the case,” the agency said last week.
When two people died after visiting a day spa in Richmond in 2023, Contra Costa County health officials found high levels of Legionella bacteria in the spa, and located two other guests who had lab-confirmed Legionnaires’ disease. Contra Costa County health officials said the hot tub at the day spa didn’t have a permit, and had never been inspected by health officials.
And in 2022, health investigators uncovered the likely source of 17 Legionella infections in Napa County — all of whom either lived, worked or had visited downtown Napa. Sixteen people had to be hospitalized, with 10 needing intensive care, and one person died, according to the CDC’s Morbidity and Mortality Weekly Report.
Investigators found high levels of Legionella bacteria in a cooling tower at what was then the Embassy Suites Napa Valley on California Boulevard, Napa County health officials said. None of the cases were guests of the hotel.
According to the MMWR, investigators said the cooling tower had malfunctioned, leading to either very little or no injection of chemicals that would prevent bacterial growth.
The report noted that cooling towers can spread Legionella bacteria over a wide area, with people living within 0.6 miles from a tower at highest risk of infection.
“Cooling towers without a comprehensive water management program or lacking routine maintenance are associated with an increased risk for Legionella colonization,” the report said.
Cooling towers were also the culprit in a large Legionnaires’ disease outbreak in New York City last year, which was linked to 114 cases, 90 hospitalizations and seven deaths. Legionella bacteria that genetically matched specimens in patients was found in cooling towers at Harlem Hospital and a nearby construction site, according to the city.
The CDC in 2024 also reported on outbreaks of Legionnaires’ disease aboard two cruise ships. Investigators found a previously unidentified source of the bacteria: “hot tubs located on private balconies, which have become more common as new ships enter service” and “are subject to less stringent operating requirements” than public hot tubs.
“Hot tubs can be a source of Legionella growth and transmission when they are inadequately maintained and operated,” the CDC said.
Times librarian Cary Schneider contributed to this report.
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