19 cases of Legionella infection have been linked to Kaiser Bay Area Hospital

Kaiser Permanente is still trying to determine the source of the bacteria responsible for 19 recent cases of Legionella infection identified at a hospital in the San Francisco Bay Area.

19 infections were linked to Kaiser Medical Center in Santa Clara. Most of those who are sick are recovering at home, Kaiser said in a recent statement.

The viruses were identified through “rigorous internal monitoring procedures,” according to Kaiser.

“Our medical center is a safe place to visit and receive care,” the health plan said.

Kaiser did not specify how sick those infected were, nor did he say specifically how the viruses were discovered.

Infections can occur when Legionella — which occurs naturally in places like lakes and streams — gets into construction water systems and people breathe in mist containing the bacteria, according to the US Centers for Disease Control and Prevention. Bacteria grow best in warm temperatures, between 77 and 113 degrees.

This disease does not spread from one person to another.

The most severe form of Legionella infection leads to Legionnaires’ disease, a severe form of pneumonia that can be fatal, the CDC says. Legionnaires’ is treatable with antibiotics, but early treatment improves the chances of recovery.

A milder form of Legionella infection called Pontiac fever can cause pain and headache.

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 exposed to Legionella do not get sick, but the bacteria can cause serious illness in some cases.

“While we are working to locate the source, out of an abundance of caution, last week we implemented additional water purification and preventative measures to ensure the safety of all patients, staff and visitors,” Kaiser said in a statement. “Due to mitigation efforts, our hospital and medical office continue to operate as normal.”

About 1 in 10 people who get Legionnaires’ disease die from complications of their illness, the CDC says. Of those who contract it during their hospital stay, about 1 in 4 are expected to die.

Legionnaires’ disease was discovered in 1976 after a large outbreak affected attendees of an American Legion convention in Philadelphia, according to the CDC. The outbreak resulted in 221 infections across Pennsylvania, and 34 deaths.

The investigators finally suspected that these viruses were airborne and infected people after contaminating the air conditioning in the convention hotel.

“Since 1976, air conditioning systems have changed and agencies around the world have stricter cleaning and sanitation standards for cooling towers and large air conditioning systems,” the CDC said.

Other ways facility managers can reduce the risk of Legionella include disinfecting cooling towers and water systems, establishing a water management system and performing regular 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 northwest corner of the city of Westminster, according to the Orange County Health Care Agency. No source has ever been found for the outbreak, “as it happens so often,” 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 two other guests had confirmed Legionnaires’ disease. Contra Costa County health officials said the hot tub at the time did not have a permit, and had never been inspected by health officials.

And in 2022, health investigators found a possible source of 17 Legionella infections in Napa County — all of whom lived, worked or visited the city of Napa. Sixteen people had to be hospitalized, 10 needed emergency care, and one 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 hotel guests.

According to the MMWR, investigators say the cooling tower malfunctioned, resulting in too little or no injection of chemicals that could inhibit bacterial growth.

The report noted that cooling towers can spread Legionella bacteria over a wide area, with people living within 0.6 miles of a tower at the highest risk of infection.

“Cooling towers without a comprehensive water management system or lack of routine maintenance are associated with an increased risk of Legionella colonization,” the report said.

Cooling towers were also responsible for a large outbreak of Legionnaires’ disease in New York City last year, which was linked to 114 cases, 90 hospitalizations and seven deaths. Legionella bacteria genetically matched to patients were found in cooling towers at Harlem Hospital and a nearby construction site, according to the city.

The CDC in 2024 also reported outbreaks of Legionnaires’ disease on two cruise ships. The investigators found a previously unknown source of germs: “hot tubs located on private patios, are becoming more common as new vessels enter service” and are “subject to stricter performance requirements” than public hot tubs.

“Hot tubs can be a source of growth and transmission of Legionella when not maintained and used properly,” the CDC said.

Times staff writer Cary Schneider contributed to this report.