Rising Tuberculosis Rates in California

California is experiencing significantly higher rates of tuberculosis (TB) compared to the rest of the United States. This increase comes amidst a rise in large outbreaks across the nation, as detailed in a recent report.

The U.S. Centers for Disease Control and Prevention (CDC) has documented a slight increase in large TB outbreaks in a study released on April 30. It revealed 24 large outbreaks (defined as having 10 or more active TB cases) from 2014 to 2016, contrasted with 50 outbreaks from 2017 to 2023.

Notably, the CDC identified trends among those at risk for large outbreaks. Generally, individuals diagnosed with TB in the U.S. are often foreign-born. However, the study indicated that 79% of those impacted by large outbreaks between 2017 and 2023 were born in the U.S. Furthermore, many among them faced substance abuse challenges, and approximately two-thirds of these outbreaks were linked to family or social networks.

The findings emerge as California reported its highest TB case count in 12 years, with 2,150 cases in 2025. The state’s TB rate stands at 5.4 per 100,000 people, notably higher than the national average of three per 100,000.

While TB can typically be treated with antibiotics, it poses serious risks, particularly to those with weakened immune systems. The California Department of Public Health reported that around 13% of TB patients died in 2023.

According to Dr. Monica Gandhi, an infectious disease expert at UC San Francisco, the CDC study highlights the persistent threat of TB, even in a wealthy nation like the U.S. “When evaluating TB in clinical settings, we often inquire about risk factors prevalent in the U.S., such as homelessness, substance use, history of incarceration, and malnutrition,” she shared.

TB can manifest as either latent or active, according to the CDC. Active TB presents symptoms and can be contagious, while latent TB does not show symptoms and isn’t transmissible but can develop into active TB at any time.

The disease spreads easily in group settings. For instance, an outbreak at Archbishop Riordan High School in San Francisco, which began with the first identified positive case in November, resulted in at least three people with active TB and over 200 with latent infections.

The school outbreak underscored the highly contagious nature of tuberculosis. Dr. Gandhi remarked, “It’s such an age-old disease.”

Dr. Matt Willis, the former public health officer of Marin County, noted that “tuberculosis thrives” when marginalized individuals lose access to healthcare. “Those are the individuals whose latent infections often go undetected and untreated, leading to active cases that further spread the disease,” he explained.

Willis, who also writes a public health newsletter, acknowledged that while strategies exist for controlling and treating TB, the disease has managed to persist for thousands of years. “Evidence of tuberculosis has even been found in mummies,” he noted. “Our immune systems have co-evolved with this organism.”