Worldwide, tuberculosis a bacterial lung disease spread mainly by coughing kills one person every 18 seconds. And because HIV activates latent TB infection, tuberculosis has become the leading cause of AIDS-related deaths in the developing world. The TB vaccine is not very effective; diagnostic tests fail to identify at least 50% of cases, and patients often fail to complete the six-month treatment regimen, which contributes to new drug-resistant strains. Of the 9 million or so new TB cases each year, about 425,000 of them are resistant to standard medicines. One severely resistant strain that emerged in southern Africa this year is virtually impossible to treat.