Narrator: This is Science Today. It's estimated that a third of the world's population is infected with tuberculosis - and that figure includes about 15 million Americans with a latent form of the bacterium. Joel Ernst, an infectious disease specialist at the University of California, San Francisco, says for years TB was thought to have been conquered.

Ernst: It certainly fell from the American consciousness, at least most of American's consciousness, after about the 1950s or so. Tuberculosis sanitaria were closed because they weren't necessary anymore. Anti-tuberculosis treatment was given as an outpatient and most people with tuberculosis who received those drugs were cured.

Narrator: Today however, stealthy strains of the microbe that causes TB have brought the disease back to pre-antibiotic days in many parts of the world, including New York and other parts of this country.

Ernst: The best chance of defeating it is going to be through the development of a more effective vaccine.

Narrator: Public health officials are also calling for better education about the disease. For Science Today, I'm Larissa Branin.