Contagious Disease Outbreaks Reach Record High In CA

Tuberculosis is the disease here — not measles. And the actual news is two things landing at once. California just logged its highest TB case count since 2013, while a new CDC analysis shows large TB outbreaks across the U.S. have become more common and are often spreading through family and social networks, not just the settings people usually picture. ### Why is California in the spotlight? Because the state’s numbers are unusually high even by U.S. standards. California reported 2,150 TB cases in 2025, up from 2,109 in 2024, and its incidence rate held at 5.4 cases per 100,000 people. That is well above the national rate of 3.0 per 100,000. CDPH says 2025 was the highest California total since 2013. (cdph.ca.gov) ### Wait — isn’t TB an old disease? Yes, but “old” does not mean gone. TB is caused by a bacterium that usually attacks the lungs and spreads through the air when a person with active disease coughs or speaks. A lot of people carry latent TB infection without feeling sick, and some later progress to active disease — which is when they can spread it. That long fuse is part of why TB is hard to eliminate. (cdph.ca.gov) ### What changed nationally? The CDC’s new outbreak paper looked at 2017 through 2023 and found 50 large TB outbreaks in 23 states, totaling 1,092 cases. For this report, “large” meant at least 10 related cases within three years. The CDC says that is more than double the 24 large outbreaks identified during 2014 to 2016, which tells you this is not just random noise. (cdph.ca.gov) ### Why are officials focused on U.S.-born residents? Because that is the part that cuts against the usual mental model. Most TB cases in the U.S. overall still occur among people born outside the country, but in these large outbreaks, 79% of patients were U.S.-born. That matters because it shows ongoing local transmission inside the U.S., not just imported infections that stop with one traveler. (cdc.gov) ### Where are these outbreaks actually spreading? Mostly through close personal networks. The CDC found about two-thirds of large outbreaks were tied to family or social networks. Only about one quarter were mainly linked to congregate settings like correctional facilities, workplaces, senior care, universities, or shelters. Basically, the image is less “single institution outbreak” and more “chains of transmission moving through everyday relationships.” (cdc.gov) ### Who is getting hit hardest? People facing instability show up more often in these outbreak clusters. Compared with other TB patients, people in large outbreaks more often reported substance use, homelessness, and incarceration. That does not mean TB is confined to those groups — it means those conditions can make diagnosis, treatment, contact tracing, and prevention much harder. (cdc.gov) ### Is this a California-only problem? No — but California is a big piece of it. The state has carried a heavier TB burden than the national average for years, and CDPH had already flagged unusually high outbreak activity in recent data. In 2023, California recorded 10 new TB outbreaks and 15 ongoing outbreaks in 15 jurisdictions, the highest number of new outbreaks and outbreak-associated cases in the prior decade. (cdc.gov) ### So what’s the bottom line? The story is not that one “contagious disease” suddenly exploded out of nowhere. It is that tuberculosis — a disease many people think of as distant or historical — is still spreading in California at a rate above the U.S. average, and the newest CDC data suggest the hardest outbreaks now move through ordinary social contact in vulnerable communities. (cdph.ca.gov) That makes early diagnosis, latent-TB treatment, and old-school contact tracing matter a lot more than people assume. (cdph.ca.gov)