Riordan High School TB investigation finds 200-plus latent infections as San Francisco expands screening and treatment

Latent TB detections rise sharply after expanded campus-wide testing

More than 200 students and staff at Archbishop Riordan High School in San Francisco have been identified with latent tuberculosis infection following an outbreak investigation that began in late 2025. Health officials reported that expanded testing found roughly 17% of the school’s community—219 people out of 1,261 students and staff—had evidence of tuberculosis infection without signs of active disease.

The new totals mark a significant increase from the findings reported in late January, when more than 50 latent infections had been detected. About 90% of the school population had been tested as the investigation continued, with remaining results still pending at the time of the latest update.

What officials mean by “latent” versus “active” tuberculosis

Tuberculosis can present as either active disease or latent infection. Active TB typically involves symptoms and can be contagious when it affects the lungs or throat. Latent TB infection, by contrast, does not cause symptoms and is not contagious; however, it can progress to active disease in a subset of people if not treated.

In the Riordan outbreak, three active TB cases had been confirmed after the initial case was identified in November 2025 and additional active cases were confirmed in January 2026. Officials also reported several suspected active cases undergoing treatment while clinical confirmation was pending.

Operational changes at school and public-health controls

As testing expanded, the school temporarily shifted away from normal in-person instruction earlier in February before largely returning to on-campus learning. Public-health controls included contact tracing and requirements tied to medical evaluation and clearance for return to campus activities during the screening phase. Officials also stated that individuals who were infectious were placed under treatment and were not considered contagious once appropriately managed.

Treatment paths offered to students and staff

Health officials urged individuals with latent TB infection to begin preventive therapy intended to reduce the likelihood of later developing active TB. A commonly used preventive approach is a short-course antibiotic regimen lasting several months, while active TB disease is treated with a longer multi-month medication protocol and closer clinical monitoring.

• Latent TB infection: preventive antibiotic therapy aimed at lowering future risk of progression.

• Active TB disease (confirmed or suspected): multi-drug treatment over months, with steps taken to stop transmission.

How the outbreak fits into San Francisco’s broader TB picture

San Francisco reports TB cases every year, with local surveillance indicating that active TB persists as an ongoing public-health concern. Citywide data for 2024 recorded 91 new active TB cases. Health officials have emphasized that, while the Riordan investigation is notable for the number of latent infections detected in one school community, the broader risk to the general public remains low when active cases are promptly identified and treated and exposed contacts are evaluated.

Latent TB is not contagious, but identifying and treating it is a key step in preventing future active cases.