Narrator: This is Science Today. Epidemics are frightening things. But for most diseases, at least they're over quickly. Not tuberculosis. Researcher Sally Blower of the University of California, San Francisco has discovered that for TB, the conventional rules don't apply.

Blower: With most other diseases such as flu or measles or chickenpox, infectious diseases, they come in pretty quickly, the epidemics peak and they decline, so epidemics that we tend to think about usually operate over weeks or months.

Narrator: But the pattern for TB is very different.

Blower: Some people who become infected with tuberculosis get tuberculosis very quickly, within a year or two, and then there are other people who get infected and then they don't develop TB for years later, it can be up to 20 years later over their lifetime.

Narrator: Which means that a TB epidemic can last for generations, because people remain infectious for so long. Blower and her team are using mathematical models to try and discover how this longest-lived of diseases can be controlled and eradicated. For Science Today, I'm Steve Tokar.