Tuberculosis infected an estimated 10.7 million people in 2024 and killed 1.23 million, making it the deadliest single infectious agent on Earth. This episode traces it from skeletons dated to 4000 BC and Egyptian mummies with spinal decay to 18th and 19th century Europe, where consumption caused a quarter of all deaths. With no germ theory to guide him, Dr. John Croghan bought Mammoth Cave in Kentucky and between 1838 and 1845 housed patients in huts underground. Every one died within a year, and Croghan later died of tuberculosis himself. Hermann Brehmer opened the first sanatorium in Silesia in 1859, yet half of sanatorium patients died within five years.

Jean-Antoine Villemin showed in 1865 that the disease was contagious, and on March 24, 1882, Robert Koch identified Mycobacterium tuberculosis. Its waxy, lipid-rich envelope lets it survive inside the macrophages sent to digest it, and the body walls it off in granulomas, the tubercles that give the disease its name. Roughly two billion people carry latent TB. The BCG vaccine of 1921 and streptomycin in 1946 helped cut European mortality by 90 percent by the 1950s, but incomplete treatment bred MDR, XDR and finally totally drug-resistant strains, first observed in Italy in 2003.

• Why the bacterium divides only every 16 to 20 hours, while E. coli takes under an hour
• Latent TB: no symptoms, not contagious, and a 5 to 15 percent lifetime chance of turning active
• True airborne spread through coughs, sneezes, speech and singing, not handshakes or shared food
• The Xpert MTB/RIF test, which finds bacterial DNA and drug-resistance mutations in hours
• In the UK, about 5,000 pounds to treat ordinary TB versus up to 70,000 pounds for MDR-TB, which can take two years