Various types of bacteria, 1889. | Oxford Science Archive/Print Collector/Getty ImagesSomething unusual happened at Archbishop Riordan High School last fall. In September, a student in the Bay Area school went to see a health care provider for a cough that wouldn’t go away. But it wasn’t until two months later that the student got diagnosed: tuberculosis. The San Francisco Department of Public Health (SFDPH) launched an investigation, which revealed a surprisingly high rate of latent tuberculosis — meaning that people were infected by the Mycobacterium tuberculosis bacteria, but their infections had not yet progressed to active and contagious disease — at the school.As of February 24, the most recent data available, four people in the school community had confirmed active tuberculosis, and an additional three active cases were suspected by the public health department.A private school in San Francisco isn’t exactly where you would expect a tuberculosis outbreak to occur. Tuberculosis is largely a disease of poverty and marginalization, and today the developing world bears the greatest burden. The vast majority of all new cases (about 87 percent) occur in just 30 low- and middle-income countries. But it used to be far more prevalent globally. Rewind the clock: On March 24, 1882, a German physician named Robert Koch announced that he had identified the cause of the illness that killed one out of every seven people in the US and Europe. Now fast-forward: Today is World Tuberculosis Day, marking the 144th anniversary of Koch’s discovery. And the disease is making a comeback in wealthy countries.Call it consumption, “the robber of youth,” the white plague — but we certainly can’t call it gone. And although it was briefly outpaced by Covid-19, in 2023 tuberculosis regained its title as the world’s leading cause of death by infectious disease. Every year, it infects about 10 million people and kills 1.5 million — despite being both preventable and curable. Counting both latent and active cases, a fourth of the entire human population may be infected with the bacteria worldwide.“The global is local and the local is global, so if we’re not able to address the global burden of tuberculosis, we’ll continue to see it everywhere,” Priya Shete, an associate professor of medicine and tuberculosis researcher at University of California San Francisco, told me. “We’ll start to see tuberculosis arise in the least expected places.” The United States has the infrastructure for tuberculosis testing and treatment, and it isn’t currently endemic here. Like much of the world, it used to be though — it may have killed as many as a quarter of all Americans during parts of the 18th and 19th centuries. But improvements in nutrition, living conditions, sanitation, and, especially, the advent of antibiotics in the mid-1900s changed things dramatically. Still, “not endemic” is a far cry from “eradicated.” After 30 years of being on the decline, tuberculosis rates are rising in the US. In February alone, it popped up in American high schools beyond the Bay Area, with confirmed cases in Long Island, New York and Seattle. One of the largest American outbreaks since the Centers for Disease Control and Prevention started reporting tuberculosis data in the 1950s happened just two years ago in Kansas, leading to 68 active cases, 91 latent infections, and two deaths. Broad disinvestment in public health infrastructure, medication supply shortages, delays in diagnosis due to the Covid pandemic, and the challenges of detecting and treating latent cases are all part of why tuberculosis is still a disease worth worrying about in the United States. The theme of this year’s World Tuberculosis Day is “Yes! We Can End TB!” That’s very ambitious, given that it’s still an ongoing challenge even in the world’s richest nation. Its persistence requires us to stay ahead in the evolutionary arms race with the pathogen, one that has possibly been on Earth for 3 million years. But there is hope — advocates are pushing for sustained investment in tuberculosis research and fighting back against funding cuts, and scientists are working to develop new treatments for this very old disease. The US v. tuberculosisTuberculosis spreads through the air, and a cough isn’t required to infect someone else — regular breathing can do the trick. “There is no country in the world that has eliminated TB or that is TB free,” Lucica Ditiu, a physician and the executive director of the Stop TB Partnership, told me. “As long as we breathe, we are all at risk.” Approximately 13 million people in the US have latent tuberculosis, which progresses to active disease in about 5 to 15 percent of cases when left untreated. Tuberculosis preventative treatment (TPT) for latent cases can clear up the infection in as little as three months with appropriate antibiotics, but a lack of access to these medications or delays in diagnosis often prevent patients from starting TPT.Left untreated, someone with active tuberculosis can infect 15 people a year.Latent infections can become active when the immune system is no longer able to keep the bacteria in check. Babies, small children, the elderly, and immunosuppressed people are at the greatest risk of converting from latent to active disease. Our health is not constant over the course of our lives: “You can have latent TB your entire life, and in your last chapter…when your immune system is suppressed, it can become active and you can start spreading it,” RC Sadoff, a public health researcher at Johns Hopkins University and team member of Zero TB in Kids, which provides tuberculosis screening and treatment for children in South Asia in settings where people live in close proximity like boarding schools and monasteries. “The powder keg is already everywhere.” Left untreated, someone with active tuberculosis can infect 15 people a year. In the US, more than 80 percent of cases result from latent cases becoming active. To complicate matters, the distinction between latent (and non-infectious) and active (and contagious) tuberculosis may not be a binary but a continuum. It’s not always clear at what point someone becomes infectious, and people can be contagious without having the traditional tuberculosis symptoms. One study estimates that subclinical cases — active infection but symptom-free — might account for 68 percent of tuberculosis transmission around the globe. “I think it is plausible that at least some of the latent TB burden we are seeing in [the Archbishop Riordan High School community] could have been transmitted by people without symptoms but still infected with tuberculosis,” Sadoff said. “I think if we understood more about subclinical transmission, maybe we could intervene sooner or more effectively [in outbreaks like these].”Compared to something exponentially more infectious like measles, tuberculosis is much more insidious. The main symptom people generally have is a chronic cough. “It gets diagnosed as everything but tuberculosis, and it goes on for a long time. So I think the danger of tuberculosis is that it can look and seem like a lot of other things that aren’t so bad,” Shete told me. When people have night sweats, another common symptom of tuberculosis, they’re more likely to think it’s hot flashes than tuberculosis, she said. “It takes a bit more vigilance to think about TB.”Delays in TB diagnosis were exacerbated by Covid, and that impact still has not been reversed. Today, new tuberculosis patients are often sicker by the time they’re diagnosed than they were in pre-pandemic caseloads. Delays in diagnosis and treatment mean more time for the disease to spread unabated, a greater chance that the bacteria will develop antibiotic resistance, and more preventable suffering. Successful tuberculosis treatment also requires sticking to a schedule of several antibiotics for months, so that the bacterium does not develop resistance to the medication.Delays in TB diagnosis were exacerbated by Covid, and that impact still has not been reversed.Another major barrier to combatting the disease in the US is cost. According to the California Department of Public Health, TPT for latent tuberculosis can cost one patient around $857 for a three- to four-month course of treatment. Diagnosing and treating a patient with active tuberculosis costs more than 50 times that. If TB and multidrug-resistant TB in the US were to reach current global average rates, the cost of treating TB cases in the US would increase to over $11 billion annually.Funding cuts to programs like USAID could lead to 2.2 million additional tuberculosis deaths in 26 countries with a high burden of the disease between 2025 and 2030. Drug-resistant cases could increase by 30 percent, requiring medications that are hard to come by and may not be FDA-approved for use in the US. We’ll feel that at home; it can cost $154,000 to treat and cure one person with drug resistant tuberculosis in America. In the US, the disease typically spreads in places without sufficient health care services to diagnose people with active TB and in places that are overcrowded, have poor ventilation, and higher rates of malnutrition like prisons and homeless shelters. As in other parts of the world, the most marginalized in the US are at the greatest risk — and treating them is more difficult.“It takes a weak health system in a high-income country to produce a tuberculosis outbreak,” Sadoff told me. “Whenever there’s a TB outbreak in America, something is wrong.”Preventing the spread of TB in the US — and beyond At Archbishop Riordan High School, 207 members of the school community have tested positive for latent tuberculosis. In order to return to in-person instruction, students had to share their test results, what treatment they were on, and how long they had taken medication, but they didn’t have to test negative for the bacteria. That’s according to a grandparent of a student infected with latent tuberculosis, who spoke to me anonymously out of fear of retaliation from the school.About 80 percent of students with latent tuberculosis were on TPT as of February 24. The school cannot legally require students with latent tuberculosis to take the medication — even though it might prevent the infection from progressing to active disease. But, the grandparent said, the school chose not to offer continued online learning options for students who aren’t receiving treatment: “To me, that’s not the way to control it or keep it from spreading.”Archbishop Riordan High School did not respond to multiple requests for comment on this policy or to several other specific questions about the outbreak. Everyone either confirmed or suspected to have active tuberculosis is on treatment and no longer considered contagious, according to the latest in a series of “TB town hall” webinars hosted for the school community. “Individuals with latent TB infection (LTBI) are allowed on campus because LTBI is not contagious,” the San Francisco Department of Public Health told me over email. It “strongly recommends that all individuals with LTBI begin and complete treatment, and we continue to educate the community about its importance in preventing future disease.” Once someone has tested positive for tuberculosis, the test will remain positive indefinitely even after successful treatment, which poses a challenge for diagnosis and future surveillance: People who are cured can be reinfected. The Archbishop Riordan High School story shows how containment anywhere is a complicated and contentious project. No matter where a tuberculosis outbreak occurs, reassuring a community that it is safe is challenging. That’s a major reason why prevention is the ideal.Health officials from the public health department stress that the risk to the broader community is low, and we don’t currently see much community transmission in the US. But the further gutting of US public health infrastructure and research funding jeopardizes our ability to keep the incidence of this disease so low.If you’d like to do something about this global threat, you can donate to Stop TB Partnership, TB Alliance, The Global Fund, Partners in Health, and Spiro, which provides screening and TPT for children in Pakistan, a country with exceptionally high rates of the disease. You can become a TBFighter, part of author John Green’s collective to address the structural causes of tuberculosis. You can also become a member of Stop TB USA, which makes it easy to contact your representatives to advocate for continued funding for public health. They also accept donations.Developing new medications, better diagnostics, vaccines that protect adults from transmission, and advocating for sustained funding into tuberculosis research, prevention, and treatment are the most powerful tools to someday end TB in the US and beyond. Even if it doesn’t happen before next year’s World Tuberculosis Day.