The bacteria that cause tuberculosis have been known since 1882 and an effective treatment was developed decades ago. And yet TB remains the world’s deadliest infectious disease. The implications of this stubborn public health puzzle are dire. In 2024, an estimated 10.7 million people fell ill with TB, but only about 8.3 million were diagnosed. Many of those who go undiagnosed eventually die from the disease. Many more unknowingly spread it. This diagnostic gap — the difference between confirmed and estimated TB cases — is the greatest barrier to an effective global response.