Tuberculosis tests reveal 204 latent cases at Riordan High in S.F.

San Francisco health officials announced today the identification of 204 latent tuberculosis cases linked to an outbreak at Archbishop Riordan High School, a private Catholic school near City College. The initial report of TB cases at the school prompted testing of students and staff.

Understanding Latent Tuberculosis

Latent tuberculosis is not contagious. Individuals with a latent infection do not exhibit symptoms and cannot transmit the bacteria to others. However, the tuberculosis bacteria can become active and infectious if left untreated. San Francisco Health Officer Dr. Susan Philip stated that “the risk to the general public remains low,” emphasizing the importance of contact tracing and testing to prevent future active cases and protect long-term health.

Did You Know? The outbreak timeline began in September 2025, with the first student seeking medical care after experiencing two weeks of coughing.

The San Francisco Department of Public Health received 1,261 test results from students and staff. Of those tested, 219 were positive for tuberculosis, with 204 cases – approximately 16 percent of those tested – confirmed as latent TB. Chest X-rays are being conducted to rule out active disease in the remaining positive cases.

School Response and Clearance

Following the initial reports of three TB cases among students in January, Riordan administrators implemented a TB clearance protocol developed in conjunction with public health guidance. This protocol allowed the school to clear 99 percent of students and 100 percent of faculty and staff, enabling a return to in-person instruction three weeks after a temporary closure and shift to hybrid learning.

Expert Insight: The public health response to this outbreak appears thorough and appropriate, according to Dr. George Rutherford, a pediatrician and infectious disease specialist at UCSF. He noted that San Francisco’s public health department is well-equipped to manage complex outbreaks.

Dr. Rutherford noted that the proportion of latent infections is significant, standing out when compared to background rates. Approximately 10 percent of people worldwide have latent tuberculosis, while in the United States, and specifically California, the rate is around 6 percent. The Riordan testing results are “above what one would suspect,” according to Dr. Rutherford.

Active vs. Latent TB

Latent TB occurs when a person inhales tuberculosis bacteria, and their immune system prevents the bacteria from causing illness. Individuals with latent TB do not feel sick and cannot spread the infection. However, without treatment, about 5 percent of those infected may develop active TB disease over their lifetime, with a higher risk – around 5 percent per year – for individuals with weakened immune systems, such as those with HIV.

Active TB typically affects the lungs and can spread through the air via coughing, speaking, or singing. Symptoms include a persistent cough, fever, night sweats, and weight loss. In severe cases, the bacteria can spread beyond the lungs to the brain or bloodstream.

As of February 20, three confirmed cases of active TB and three suspected active cases have been identified within the school community. All confirmed and suspected active cases are currently undergoing treatment, and health officials report that there are no contagious cases on campus.

Looking Ahead

Public health officials have not released details regarding how the transmission occurred. No related active TB cases have been reported at other San Francisco schools, and no additional actions are currently required outside the Riordan community. Further investigation will reveal clustering of cases within specific groups or activities at the school, such as choir, where airborne transmission may be more likely.

Frequently Asked Questions

What is the difference between latent and active TB?

Latent tuberculosis is not contagious and doesn’t make you sick. Active TB is contagious and can make you sick.

How many cases of TB have been identified at Archbishop Riordan High School?

As of February 20, three confirmed cases of active TB and three suspected active cases have been identified. 204 cases of latent TB have been confirmed.

Is the general public at risk?

According to San Francisco Health Officer Dr. Susan Philip, “the risk to the general public remains low.”

Given the ongoing monitoring and treatment efforts, what further steps might public health officials take to ensure the long-term health of the Riordan community?