San Francisco health officials have announced 204 cases of latent tuberculosis (TB) associated with an outbreak at Archbishop Riordan High School, a private Catholic school near City College. While not contagious, latent TB can develop into active TB disease if left untreated.
The San Francisco Department of Public Health began investigating after three students were diagnosed with active TB cases since November 2025. This prompted testing of students and staff, with results received as of . Of the 1,261 tests completed, 219 were positive for tuberculosis, with 204 confirmed as latent TB – approximately 16 percent of those tested.
Latent TB occurs when a person inhales TB bacteria, but the immune system prevents the bacteria from causing illness. Individuals with latent TB do not experience symptoms and cannot spread the infection. However, without treatment, there is a risk – roughly 5 percent over a lifetime – that the latent infection will progress to active TB disease. This risk is elevated in individuals with weakened immune systems, potentially rising to 5 percent per year.
Active TB typically affects the lungs and is spread through the air when an infected person coughs, speaks, or sings. Symptoms include a persistent cough, fever, night sweats, and weight loss. In severe cases, the infection can spread beyond the lungs to other organs.
San Francisco Health Officer Dr. Susan Philip stated that “the risk to the general public remains low.” Public health officials emphasize that contact tracing and testing are crucial to preventing future active cases and protecting long-term health. Currently, three confirmed cases of active TB and three suspected cases have been identified within the school community, all of whom are receiving treatment. Health officials report that there are no currently contagious cases on campus.
The school temporarily closed and transitioned to hybrid learning in early February, implementing a TB clearance protocol developed in conjunction with public health guidance. According to officials, 99 percent of students and 100 percent of faculty and staff have been cleared, allowing a return to in-person instruction three weeks after the initial closure.
Dr. George Rutherford, a pediatrician and infectious disease specialist at UCSF, described the public health response as “thorough and appropriate.” He noted that the proportion of latent infections identified – 16 percent – is significant, exceeding typical background rates. “About 10 percent of people in the world have latent tuberculosis. In the United States, it’s lower — on the order of 6 percent in California,” Dr. Rutherford explained. “The Riordan testing results are above what one would suspect.”
Dr. Rutherford cautioned that the significance of the 16 percent figure depends on the specifics of the testing. If the testing was accurate, determining whether the elevated rate represents a clustering of cases within specific groups – such as a particular grade or extracurricular activity – is important. He highlighted that activities involving forceful exhalation, like choir, could potentially contribute to increased transmission of airborne bacteria.
Public health officials have not yet released details regarding the mode of transmission. However, they have confirmed that no related active TB cases have been reported at other San Francisco schools, and no additional actions are currently required outside of the Riordan community.
The outbreak timeline began in September 2025, when a student sought medical care after experiencing a two-week cough. This case was confirmed as active TB in November, initiating contact tracing and expanded testing. Two additional active cases were confirmed in January 2026, leading to mandatory testing for all students and staff, as well as health advisories to local clinicians and information sessions for pediatricians and community town halls.
It’s important to remember that latent TB is not an immediate health threat. However, treatment is available to prevent progression to active disease. Individuals concerned about potential exposure should consult with their healthcare provider for testing and guidance.
