TB outbreak in a school, measles in the Magic Kingdom, and flu
The CA Dose, February 5, 2026
It’s been a busy week for California public health workers—tuberculosis in the North, measles in the South, and flu across the state. This week’s Dose is covers a lot of ground—we’ll start in San Francisco, with TB.
Controlling a high school TB outbreak
Archbishop Riordan High School in San Francisco temporarily closed in person classes due to a tuberculosis (TB) outbreak this week. So far, three cases of active TB disease and another 50 with latent TB infection (LTBI) have been reported.
TB might seem like a disease of the past. This outbreak is a reminder that it’s still very much with us. It’s a good time to brush up on the basics of this unique disease.
What is “latent TB”? Most infectious diseases follow a common pattern: we get infected, develop symptoms within a few days, fight the infection, and hopefully recover. TB is different. Instead, most people infected with Mycobacterium tuberculosis, the bacteria that causes TB, never get sick from it and don’t even know they’re infected.
We call that state—infected, not sick, and not contagious—latent TB. In latent infection, our immune system contains the bacteria, and it sits dormant, usually somewhere in the lung. The problem is this: if our immune systems weaken at any point in life, latent TB infection can progress to active, life threatening disease.
Only 5-10% of infected people actually get sick with TB disease, and the illness can happen decades after infection. TB’s strategy for spreading is a little like a farmer casting handfuls of seeds, knowing a few will eventually take.
“Active TB” describes symptomatic illness—usually cough, fevers, weight loss—when the bacteria spreads through the air and can infect others. In California, about 1 in 6 people with active TB die from the illness. It’s generally treatable with a six-month course of antibiotics, if it’s caught early enough.
How do I know if I have latent TB? If you don’t have known risk factors for TB exposure, it’s very unlikely you’re carrying the bacteria. So the first step is a screening questionnaire, to find out if you need lab testing. Here’s the screening questionnaire for the state of California. This might be familiar to you—it’s used across the state for clearance for adults to work in certain settings, including volunteering in schools. It’s best to walk through this with health care provider who can make sure you understand what’s being asked.
If you have any of these risk factors, the recommended next step is a test for LTBI through your medical clinician. There are two main types of tests: the interferon gamma release assay (IGRA), and a tuberculin skin test (TST).
If either of these tests are positive, the most common next step is LTBI treatment (after a chest X-ray to make sure you don’t have active disease). The goal is to kill the bacteria while it’s dormant, before you can get sick or infect others. The treatment for latent TB is usually three to six months of antibiotics. If people stick to the course and don’t miss doses, it’s highly effective.
So, getting back to Riordan… The systematic screening of the school community—adults and kids—uncovered 50 people with latent TB. The three active cases didn’t necessarily cause all the latent cases on campus; more likely, the screening revealed previously undetected, latent infection in the community.
Why focus on latent TB? The Riordan experience is a microcosm of our pattern in California. In fact more than 2 million Californians are estimated to have latent TB, and most are unaware and untreated. Last year California enacted a new law to increase rates of treatment for LTBI: Assembly Bill 2132 requires adults in primary care be offered TB testing if risk factors are identified in the screening survey, with follow-up care for treatment.
My take: When I served as TB controller for the Navajo Nation in the early 2000s, I saw what universal screening and treatment can do to control the spread of TB. In the 1950s, the burden of TB disease in Navajo communities was among the highest in the nation. Until a woman named Annie Dodge Wauneka, a Navajo elder and public health activist (her slogan was “I’ll go and do more”) pioneered community-centered TB screening and treatment across the reservation. TB rates declined dramatically over a period of just a few years. Her strategy, to bring TB medicine daily to TB patients’ homes—called directly observed therapy (DOT)—is now a mainstay of modern TB control programs.
The Riordan school outbreak is receiving the kind of close attention that Annie Wauneka proved can control TB. I’m confident they’ll be back to business as usual soon. This latest outbreak reminds us that there’s still a lot of latent infection out there, and that screening and treatment—consistently and systemically—is central to TB prevention.
Measles in the Magic Kingdom (again)
Orange County health officials have confirmed a measles case linked to an international traveler who spent time at Disneyland and traveled through LAX on January 28. This is California’s ninth case in January—well above last year’s average of less than two cases per month.
In last week’s post, when I noted our defenses against measles will be tested this year, I didn’t expect such a stark example of this problem so soon.
While a single measles case isn’t necessarily newsworthy anymore, this one is notable because of the likelihood we’ll see more related cases. This is how California’s major outbreak began a decade ago—an unvaccinated visitor, exposing hundreds to thousands of people to measles in the busy mix of humanity that is Disneyland.
The 2014-15 Disneyland outbreak led to at least 131 measles cases in California. As Marin’s health officer at the time, I remember watching with concern as cases in unvaccinated children who’d been exposed cropped up across the state, sparking local outbreaks, including one in our own community.
Disneyland draws visitors from across California, the U.S., and internationally, and most people who were exposed last week have returned home. Symptoms typically appear 7–14 days after exposure, so anyone infected last week is just entering the window when illness begins to show. Early symptoms include fever, cough, runny nose, and red eyes, followed by a widespread rash.
People who may have been exposed should check their immune status (if you’re up to date you have a lot less to worry about), monitor for symptoms, and contact a healthcare provider with any concerns.
Remember, the single most important factor determining if a child who’s been exposed develops the disease, and becomes infectious to others, is vaccination status. Talk to your health care provider or visit MyTurn.ca.gov to make a vaccine appointment. If you’re unsure if you’re vaccinated, check your CA Digital Vaccine Record (DVR) or ask your health care provider.
Infectious disease “weather report”
Flu: The most important change from last week’s update is a resurgence of flu activity across the state. Last year we witnessed a “double peak” in flu activity—where rates declined slightly for about two weeks in January, then rebounded to even higher levels. This seems to be the pattern this season as well.
RSV continues a slow increase statewide, and more children and older adults are being hospitalized.
Covid 19 activity remains low in California.
We’re still in the thick of virus season. Masking up in crowded, indoor places can help prevent infection.
If you’re sick, stay home if you can, and wear a mask around others.
A flu test can help diagnose illness early enough to benefit from antiviral treatment. Contact your healthcare clinician for treatment options, following the latest guidance.
Vaccines are available across California. You can visit MyTurn to schedule a shot today.
Who are you?
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Bottom line
Behind each issue touched on in this edition—controlling school TB outbreaks, tracking measles across busy gathering places, monitoring flu levels and ensuring access to vaccines—is a team of public health champions working day and night to protect us. If you’re one of those people, we see you and we’re grateful. That’s it for this week!
Love,
Matt
Dr. Matt Willis is the author of Your Local Epidemiologist in California. A California native, he’s served as a primary care physician, CDC epidemiologist, and public health officer for Marin County, where he guided the pandemic response. He lives in Marin with his wife, children, and their dogs Teddy and Ramona.
Appreciate the TB review!