Tuberculosis Outbreak at Archbishop Riordan High School

Recent data reveals that nearly 18% of students and staff at Archbishop Riordan High School in San Francisco have been diagnosed with either latent or active tuberculosis during an outbreak that began in November of last year.

Testing has shown that out of the tested population, 96% participated. A total of seven individuals were diagnosed with active TB, while 241 were identified with latent cases, as per information provided by the San Francisco Department of Public Health. The results were communicated to the school’s community on April 27.

Four active cases and three suspected cases were reported back in February, and now those suspected cases have been confirmed as active TB. Following this, another round of testing took place in March to ensure the safety of the entire school community.

The health department stated that data from the March testing indicated a significant reduction in transmission, noting that repeat mass testing isn’t necessary anymore. However, new testing is set to take place today, primarily for individuals who were recently in contact with confirmed cases or those who belong to a small group with newly identified latent TB.

Dr. Monica Gandhi, an infectious disease specialist at UC San Francisco, mentioned that TB is slow-growing, meaning it can take eight to ten weeks for symptoms to present after exposure. She emphasized that every active case resets the timeline for testing, triggering contact tracing for those in proximity.

Gandhi elaborated that a TB cluster is officially defined as having four or more active cases, which makes this situation significant given the seven active cases reported. Tuberculosis, a bacterial disease known for its long history, can present itself in two forms: active, which transmits and shows symptoms like cough or weight loss, and latent, which remains asymptomatic. Importantly, latent TB can evolve into active TB later on.

Both forms can be treated with prolonged antibiotic regimens, although Dr. Gandhi expressed concern about the unusually high percentage of latent TB cases within the school population. Such rates are typically seen in low-income countries rather than among children in the U.S.

As for the school, responses to requests for comment were not returned by press time. The California Department of Public Health has clarified that the last known infectious individual was on campus on February 19. Currently, only those with TB clearance documented at the school are permitted on campus or at related events. Of those diagnosed with latent TB, 95% are undergoing treatment or have completed it, while all individuals with active cases are receiving care.

In California, tuberculosis remains a significant concern, having reached a 12-year high in 2025 with 2,150 reported cases. The state’s rate, at 5.4 infections per 100,000, surpasses the national average of roughly 3 per 100,000.