It may not be marked on your calendar, but today, March 24 is World TB Day , created to remind people of the massive global health problem caused by tuberculosis. On this day in 1882, the brilliant microbiologist Dr. Robert Koch announced his stunning discovery that TB is caused by infection with a bacterium,Mycobacterium tuberculosis. At the time, TB killed one in seven people in Europe and the Americas. Now, 132 years later, TB still kills more people than any other infection save AIDS – and many AIDS patients worldwide actually die of TB. Why does TB continue to rage despite decades of scientific progress, and why am I nonetheless hopeful that great improvements in stopping TB are possible?