Uptick in tuberculosis raises alarm in California

Illustration shows orange, rod-shaped bacterial cells in a greenish-blue film
Tuberculosis is a bacterial infection that can be latent in the body and then later activate, if the immune system is weakened by a health condition or age. (Image credit: KATERYNA KON/SCIENCE PHOTO LIBRARY via Getty Images)

California reported around 2,100 cases of active tuberculosis (TB) in 2023, a 15% jump from the previous year, preliminary data show. Most of the cases involved people with "latent" infections that became active, causing them to get sick and become infectious to others.

The California Department of Public Health (CDPH) issued an advisory flagging this "substantial increase" in active TB, although the department noted that the uptick represents a return to pre-pandemic numbers.

In 2019, prior to the start of the COVID-19 pandemic, the state recorded 2,100 cases of active TB, and similar numbers were reported in 2018 and 2017. Excluding the pandemic's peak years, California's annual tuberculosis counts have hovered around this level for about a decade, down from a peak of over 5,000 in the early 1990s.

Nonetheless, health officials wanted to alert doctors of the 2023 uptick and highlight the ongoing need to test and treat people for the bacterial disease.

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"What we want providers to know is that when any individual comes to them presenting with respiratory symptoms, they need to start thinking about is: Is this potentially a person who is at risk of having TB?" Dr. Regina Chinsio-Kwong, Orange County's health officer, told The Los Angeles Times.

Tuberculosis is a bacterial disease caused by the microbe Mycobacterium tuberculosis. It usually affects the lungs and spreads through the air via coughs and sneezes. From the lungs, the infection can spread to other parts of the body, such as the kidneys and brain.

Most people infected with M. tuberculosis don't get sick; their immune systems are able to suppress the infection, resulting in latent TB that can't spread to other people; if activated later, though, the infection could then spread. About 5% to 10% of people infected with the bacteria will develop active TB, the World Health Organization estimates. This is more likely in people with diabetes, malnutrition or weakened immune systems, including those with HIV, as conditions that impact the immune system make the body less able to keep the infection in check.

There's a vaccine for TB that's regularly given in countries with high case counts, such as Algeria, Mexico and Vietnam, but not in the U.S., where the risk of infection is comparably low. The U.S. provisionally reported more than 9,600 TB cases in 2023, with most reported among people not born within the country. 

Both latent and active TB can be treated with antibiotics; treating the latent form prevents the infection from activating

About 85% of California's 2023 cases were from people whose latent TB became active, CDPH noted in a report. About 5% were among people who arrived in California from outside the U.S. with active TB, and the remaining 10% resulted from recent TB transmission. Most of the people with active TB were born outside the U.S.

Several factors may explain the state's recent rise in cases, CDPH noted in its report. Safety measures taken during the peak of the pandemic may have reduced both the spread of and testing for TB, so now we're seeing a rebound. At the same time, insufficient testing and treatment for latent TB may have fueled a rise in active cases. In addition, following pandemic-related pauses in travel, people are again traveling to California from places with high levels of TB, the report noted.

This article is for informational purposes only and is not meant to offer medical advice.

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Nicoletta Lanese
Channel Editor, Health

Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers' work.