A tuberculosis (TB) outbreak at Archbishop Riordan High School in San Francisco has infected nearly one in five tested students and staff, according to new data released by the San Francisco Department of Public Health (SFDPH).
Health officials said 252 people, or about 18 percent of the school community tested, were diagnosed with either latent tuberculosis infection (LTBI) or active TB disease between November 10, 2025, and April 22, 2026.
The outbreak investigation began after cases were first identified in November of last year.
Among those cases, seven people were confirmed to have active TB disease. Three previously suspected cases were recently verified as active infections. Officials said all seven individuals are receiving treatment, and the last infectious person was on campus on February 19.
In a letter sent to families and staff on April 27, SFDPH said recent testing shows “a strong reduction in transmission.” Since March 9, 1,135 additional test results have been reviewed, with 19 new positive cases identified.
SFDPH said further testing this spring will focus only on people with recent exposure to confirmed cases or individuals linked to newly identified latent infections. Testing clinics were scheduled for this week.
TB is caused by the bacterium Mycobacterium tuberculosis, according to the Centers for Disease Control and Prevention (CDC). The disease usually affects the lungs and spreads through the air when a person with active TB coughs, speaks, or sings.
The CDC says two TB-related conditions exist: latent TB infection and active TB disease. People with latent TB do not have symptoms and are not contagious, but the infection can later become active if untreated. Symptoms of active TB include a persistent cough, fever, night sweats, chest pain, weight loss, and fatigue.
SFDPH reported that 241 people at Archbishop Riordan were diagnosed with latent TB infection, while four additional chest X-ray reviews remain pending. Officials said 95 percent of those diagnosed with latent TB are either undergoing or have completed treatment.
The outbreak comes as California faces rising TB rates. The state’s public health department reported a “substantial” 2,150 TB cases in 2025, the highest number in 12 years, with California’s infection rate exceeding the national average.
Globally, the World Health Organization reports that eight countries accounted for roughly two-thirds of TB cases in 2024: India, Indonesia, Philippines, China, Pakistan, Nigeria, Democratic Republic of the Congo, and Bangladesh.
– – –
Kaitlin Housler is a reporter at The Tennessee Star and The Star News Network. Follow Kaitlin on X.
