San Francisco TB Outbreak: Active vs. Latent Explained

A local outbreak at a San Francisco school highlights the differences between active and latent tuberculosis.

Published on Feb. 12, 2026

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A spate of tuberculosis (TB) cases at Archbishop Riordan High School in San Francisco has sparked concerns about the difference between active and latent TB. While active TB is an infectious disease that can cause serious symptoms, latent TB is a "sleeping" form where the bacteria remain dormant and cannot be transmitted to others. However, latent TB can still reactivate and lead to active TB disease if left untreated. The San Francisco Department of Public Health has identified over 50 people with latent TB infection in addition to the three active cases.

Why it matters

Tuberculosis remains a major global health threat, causing around 1.2 million deaths annually worldwide. While active TB is the more serious and contagious form, latent TB affects millions of Americans and can still be deadly if it progresses to active disease. Raising awareness about the differences between the two forms and the importance of testing and treatment is crucial to containing TB outbreaks in the community.

The details

Active TB is an infectious disease caused by bacteria that spreads through the air when people with active TB in their lungs cough, sneeze, or speak. Symptoms include a persistent cough, unexplained weight loss, fever, and night sweats. Latent TB, on the other hand, occurs when a person is infected with the TB bacteria but the immune system keeps the bacteria dormant, meaning they have no symptoms and cannot transmit the disease to others. However, latent TB can reactivate and progress to active TB disease, especially if a person's immune system becomes weakened.

  • In late January 2026, the San Francisco Department of Public Health declared a TB outbreak at Archbishop Riordan High School.
  • The department diagnosed and began treating three people from the school with active TB disease.

The players

Priya Shete

An associate professor of medicine and epidemiology at UC San Francisco and co-director of the UCSF Center for Tuberculosis.

San Francisco Department of Public Health

The local public health agency that declared the TB outbreak at Archbishop Riordan High School and identified over 50 people with latent TB infection.

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What they’re saying

“Latent TB can "wake up," and cause active TB disease. Up to 13 million Americans are estimated to have latent TB, although only around 10,000 develop TB disease each year.”

— Priya Shete, Associate Professor of Medicine and Epidemiology, UC San Francisco (Mirage News)

“Our research has shown that one of the biggest gaps in preventing TB in the U.S. is getting people who are at risk screened and tested. Without this early step in care, we can't get people who need it on preventative treatment.”

— Priya Shete, Associate Professor of Medicine and Epidemiology, UC San Francisco (Mirage News)

What’s next

California recently passed a law mandating that primary care providers offer screening and testing for latent TB infection to anyone at risk, which could help identify more cases and get people on preventative treatment.

The takeaway

The San Francisco TB outbreak highlights the importance of understanding the differences between active and latent TB, and the need for widespread testing and treatment to prevent the spread of this deadly disease, even in its dormant form.