Kaiser Permanente's Santa Clara Medical Center announced Friday that environmental testing has identified a rooftop cooling tower as the most likely source of a Legionella pneumophila cluster that has sickened multiple patients and staff at the facility over the past week. The Santa Clara County Public Health Department confirmed it is working alongside Kaiser Permanente's infection control team and the California Department of Public Health to contain the outbreak and prevent further exposure.

Hospital officials said all affected cooling tower systems have been taken offline pending hyperchlorination treatment and mechanical cleaning, a standard remediation protocol under CDC guidelines for healthcare-associated Legionella outbreaks. The facility's water management plan, required under CMS regulations introduced after high-profile hospital outbreaks in the 2010s, is being reviewed by an independent environmental health contractor. No new confirmed cases have been reported since Tuesday, officials said, though contact tracing of patients discharged over the past 30 days continues.

Santa Clara County Public Health Officer Dr. Marty Fenstersheib issued a statement Friday urging any former patient or visitor who developed pneumonia-like symptoms — including fever, cough, and shortness of breath — within two weeks of visiting the facility to seek immediate medical evaluation and inform their treating physician of the potential Legionella exposure. Legionella is not transmitted person-to-person, health officials stressed, and the risk to the broader community remains low.

Kaiser Permanente said in a prepared statement that patient safety is its 'highest priority' and that it is cooperating fully with county and state investigators. The health system said it expects cooling tower remediation to be completed within 72 hours and that clinical operations at the Santa Clara campus remain open with no service disruptions. Infection control precautions have been heightened across inpatient wards as a precautionary measure.

Public health experts noted that hospital-acquired Legionellosis carries a case fatality rate of roughly 10 to 15 percent in immunocompromised patients, making rapid source identification critical. The episode is expected to draw renewed scrutiny to CMS water management compliance requirements across California's hospital network, with state regulators indicating they may conduct unannounced inspections at other large acute-care facilities in the Bay Area in coming weeks.