Why the Bay Area has been a tuberculosis hotspot for more than a century

Tuberculosis, the bacteria often associated with the deaths of Victorian-era monarchs, was recently contracted by more than 200 high school students in San Francisco. The outbreak served as a reminder of the historical foothold it has in the Bay Area.

Alameda, Santa Clara, San Francisco and San Mateo counties each rank among the top 10 in the state when it comes to cases of tuberculosis, or TB, with rates as high as three times the national average.

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“We have a large reservoir of people with (latent tuberculosis infections), and they should be tested and treated. But they’re not, for a variety of reasons,” said Dr. Amit Chitnis, tuberculosis controller for the Alameda County Public Health Department.

While cases of tuberculosis are still exceptionally rare compared to developing countries, it reclaimed the title as deadliest infectious disease from COVID-19 in 2023, according to the World Health Organization.

The Bay Area has long been an epicenter for the disease on the West Coast because of its ports and as an immigration checkpoint for migrants from places such as Asia and Latin America.

For about 50 years until the 1940s, immigrants were largely processed through Angel Island, 740-acres of land in the San Francisco Bay only accessible by ferry or private boat.

If immigrants were found to have an active case of tuberculosis, they were sent to the island’s quarantine station so they could be treated with a strict regiment of isolation, fresh air and extensive rest until doctors cleared them, according to the CDC.

Currently, U.S. Citizen and Immigrations Services screens migrants for active infections, but those with a dormant strain, known as latent TB, pass through undiscovered.

More than 90% of active cases in the Bay Area now occur among immigrants that have come from countries that lack easy access to vaccines, according to Stanford tuberculosis researcher Jason Andrews. The rate is highest among people born in the Philippines and Vietnam, followed by India, China and Mexico.

“TB thrives where there are disparities. It thrives in neglected communities, in settings where we have undernutrition,” Andrews said. “It’s helpful to look at TB as a quintessential disease of both poverty as well as inequality and poor social support systems.”

In Alameda County, cases are centralized in Oakland’s Chinatown with other elevated rates found in South San Leandro, West Hayward, Union City and South Fremont, according to a 2024 Alameda County Public Health Department report.

The San Mateo Public Health Department found that 45% of cases mostly occurred in Daly City. Santa Clara County’s rates were highest in San Jose — which had the second highest rate in any major metropolitan area in the continental U.S. in 2021, according to Santa Clara County public Health.

In nearly two-thirds of active cases, the person has lived in the U.S. for more than 10 years, according Bay Area public health agencies. Those at greatest risk of having latent TB become an active infection are those who’ve been exposed to someone with active TB, people who have weakened immune systems from diseases such as HIV and diabetes, and young children under 5 years old.

Tuberculosis is indiscriminate in who it infects. In 1929, Col. P. S. Rawls, a medical officer at the Arroyo del Valle Sanitarium south of Livermore, contracted the disease “either (from) his experiences in the World War or close association with patients,” the Oakland Tribune wrote at the time.

As to why a late January outbreak occurred among children at a private high school in San Francisco, screening for latent TB is absent.

This detection gap is the primary purveyor of the disease in the U.S. and is the focus of public health professionals. Identifying and treating latent TB has been lauded as a key strategy to prevent outbreaks among migrant communities and the native public for more than a generation by public health experts, according to a 2002 Cornell University study.

“Although the bulk of the world’s tuberculosis burden exists in the developing world, the phenomenon of globalization has brought it right to our doorstep, and has reminded us that we live in an increasingly interconnected world,” said lead author Dr. Kamran Khan.

But screening for latent TB — with treatment that can last up to nine months to fully eradicate the bacteria — is an expensive endeavor with a low payoff, considering that only 5% of people with latent TB will develop into an active case.

Chitnis said that public health agencies’ focus is on cases and contacts during an outbreak “because they’re the highest risk population.”

In recent years, the U.S. has lost ground to a disease that it had all but defeated due to significant cuts to institutions charged with combating disease and protecting vulnerable populations at risk, Andrews said. These cuts contribute to deeper poverty, more crowded living situations and poor sanitation that create an ideal environment for the world’s deadliest disease, the Stanford researcher said.

“TB is like a barometer for our public health system. … It’s a very visible and tangible problem that we should be able to control and eliminate in the United States,” Andrews said. “The fact that we’re losing ground on this is a sign of sickness of our medical and public health institutions, but also the social support networks that we have for the populations that are at greatest risk.”