After declining for three decades, tuberculosis (TB) rates in the U.S. have been increasing steadily since 2020, according to a Centers for Disease Control and Prevention report from the end of 2024. It’s a disturbing trend given that 1.5 million die from TB every year, making it the world’s most infectious killer.

Now a recent outbreak in Kansas City, Kansas, has gained national attention and concern. Though the Centers for Disease Control and Prevention has since refuted claims that this is the largest outbreak in recorded U.S. history, the numbers are still historically high: As of January 24, two people have died from TB, 67 are being treated for active infections, and another 79 have latent infections.

Nationwide, 2023 saw the highest number of cases reported in the last decade. Most of these recent cases are not instances of novel transmission, but sudden activation of latent infections that were undetected or improperly treated.

While TB impacts thousands nationally and millions around the world, "most people in the U.S. are not at risk of developing TB,” says Philip LoBue, director of the CDC’s Division of Tuberculosis Elimination. 

Compared with high TB incidence countries like India, China, and the Philippines, the chance of infection in the U.S. is still one of the lowest in the world. But the recent trend reversal has raised questions—and some alarm bells—among infectious disease and public health experts. Here they offer insight into the causes and implications of the latest outbreak and sudden upswing in cases.

Tuberculosis is one of the oldest and deadliest diseases in human history. For millennia, the infection has afflicted people around the globe, earning ominous nicknames like “the white plague,” “consumption,” and even “the robber of youth.” A century and a half ago, TB was essentially a death sentence—roughly 80 percent of active infections were fatal. Since then, rates have been on the decline in the U.S. and abroad, thanks to new vaccines, diagnostics, and antibiotic treatments.

The disease is caused by a highly contagious bacterial infection that primarily affects the lungs but can also damage the kidneys, heart, bones, joints, and blood vessels. If it spreads, it can cause meningitis, swelling of the brain and spinal cord, or hepatitis, inflammation of the liver.

"Even the people who don't die of the disease, they're hospitalized [and] have a lot of long-term problems from having TB,” says Priya Shete, associate medical professor and co-director of the University of California, San Francisco Center for Tuberculosis.

TB transmits through prolonged exposure to infectious airborne particles, such as from coughing or sneezing. A person infected with TB often does not display symptoms or know they’re sick for weeks or even years—called a “latent” infection. But the infection may become active, and contagious, at any time. 

Even if the bacteria is detected and an effective antibiotic is prescribed, the treatment regimen is long—several months—which makes patient compliance difficult. 

“We need constant surveillance and suppression to keep TB in a latent form,” says Jeffrey Cox, professor of immunology and pathogenesis at University of California, Berkeley. “If you remove that pressure, the bacteria can then start growing again.”

While both preventable and curable, TB remains a leading infectious killer worldwide, claiming over a million lives every year. The disease affects millions in every country and age group, but hits particularly hard in low- and middle-income populations.

From a public health perspective, it’s no surprise that tuberculosis counts have been on the rise since 2020. When the pandemic hit, reporting of other communicable diseases like TB initially plummeted as the majority of resources went towards COVID. 

“Most countries actually had a dip [in cases] from 2019 to 2020,” Cox says. “But that doesn’t mean that TB went down.”

In fact, the pandemic-era emphasis on coronavirus tracing and treatment may have allowed TB infections to multiply unchecked. 

“A lot of those lower priority activities of health care—maintenance and prevention—were deferred,” says Shete. “We weren’t doing a great job prioritizing TB prevention.”

Cox describes a sort of snowball effect: If people don’t get tested or report infections, they don’t get the treatment they need and can transmit the infection to others. Waning mask-wearing and increased travel can also exacerbate the spread.

Compared with previous caseloads, new TB patients are “often more sick at the time that they’re diagnosed,” Shete says. During the pandemic, some physicians may have misidentified or failed to take their symptoms seriously. “It can be kind of the slow burn of a disease where people start to lose weight, they start to feel crummy, they have a chronic cough, and maybe not seek care as quickly.”

LoBue agrees, citing “the similarity of pulmonary TB disease and COVID-19 symptoms” and disrupted health care access during the pandemic as key factors in the initial drop, then rise, in cases. 

As before the pandemic, most recent cases—a whopping 80 percent—occur when untreated, latent infections become active. This most often happens to people whose immune systems are weakened, particularly from diseases like HIV or certain immune-suppressing medications, according to LoBue. In contrast, a healthy immune system could keep the infection at bay indefinitely.

As for the Kansas City outbreak, officials have yet to determine its exact cause, but Cox says it points to the ever-present threat of TB in dense urban areas—even in low-risk countries. 

“TB is not going away. It might be low here, but it's all over the world,” he says. “There’s going to be invariable flare-ups from time to time.” And in places like the U.S. where TB is not endemic, he adds, “it can spread like wildfire.”

Cox, for his part, is most concerned about potential drug resistance. The worst case scenario, he says, is if experts determine that patient zero carried an antibiotic resistant strain of TB, which would complicate treatment. Still, he echoes local health officials who assert that the risk to the general public is “very low.” While Cox understands concern within the immediate Kansas metropolitan area, he says the odds of it spreading further are slim. “There's no reason to panic right now.”

Within the U.S., those most susceptible to TB continue to be people born in, or frequent visitors to, countries where TB is common, working or living in riskier settings like schools and high-density housing, or those with weaker immune systems, according to Shete.

“Tuberculosis, just generally speaking, is often called a ‘disease of poverty,’” she says. People experiencing food insecurity, poor access to basic health services, and inadequate or crowded living conditions are at higher risk of infection and often lack the resources for testing or treatment.

Of people born in the U.S., TB rates are highest among those “who have historically been minoritized or marginalized, socioeconomically or racially or ethnically,” Shete says, including Black and Latinx populations. According to the latest CDC report, Black Americans represented the largest number—33 percent—of U.S.-born TB cases, followed by Hispanic and white Americans. 

Still, Cox emphasizes that national numbers “pale in comparison” with the rest of the world. And whether the increased cases are just a “blip” or continue to trend upwards remains to be seen. “Until we have more years of data, we can't say for sure,” agrees the CDC’s LoBue.

Experts urge people to stay informed about TB, without raising unnecessary alarm. Shete says it’s important to remember it’s fully preventable, diagnosable, and treatable.

Those outside of high-risk groups generally don’t have to worry unless they notice symptoms or are exposed to someone with an active infection. That said, Shete adds, “I hesitate to make it less important to most people only because it just takes one person in your community to have TB.”

The greater burden falls on healthcare professionals and the public health system. Particularly among high-risk populations, Shete says that physicians should regularly screen for TB. These preventative measures should be included in Medicare coverage, which is not always the case. Just last year, the U.S. Preventive Services Task Force issued a recommendation for screening asymptomatic adults at increased risk of latent tuberculosis infection for the first time since 2016.

Long-term management of TB cases will require ongoing investment in clinical research and the development of more effective diagnostics and antibiotics, Cox says.

“It does take that kind of infrastructure and constant surveillance and funds from the government to keep those programs going,” Cox says. 

Ultimately, the risk of TB for U.S. residents is mercifully low. But effective mitigation of the infection at home relies on attacking it on a global scale. The U.S. has made this a priority, through international programs like USAID’s Global TB Strategy and the CDC’s Division of Global HIV & TB, which is working to combat the two epidemics simultaneously. 

As Shete says, “Whatever is happening in the world is going to affect us too in the U.S.”