Tuberculosis: 17 Questions and Answers

Atlanta lawyer Andrew Speaker has been released from a Denver hospital where he was being treated for tuberculosis.

Speaker's story has raised questions about tuberculosis. Here are 17 questions and answers.

What is tuberculosis?

Tuberculosis (TB) is an infectious disease caused by a bacterium that spreads through the air, usually through coughing.

How common is tuberculosis?

According to the World Health Organization, more than 8.8 million people worldwide are infected with tuberculosis, and almost 1.6 million people per year die from tuberculosis.

There are about 14,000 cases of tuberculosis every year in the U.S., according to Carol Dukes Hamilton, MD, an infectious disease specialist at Duke University Medical Center and the medical director of North Carolina's tuberculosis control program.

"TB continues to be a really major problem in the world. It's huge," Hamilton says.

"The most common thing people say is, 'TB? I thought it was gone.' It's really not gone. And it can surge. It can come back. We don't want to be alarmist, but we have to continue to pay attention."

If millions of people have tuberculosis, why is Speaker's case different?

Unlike most tuberculosis patients, Speaker has multidrug-resistant tuberculosis (MDR TB). He was earlier thought to have extensively drug-resistant tuberculosis (XDR TB), which is even rarer.

Multidrug-resistant TB doesn't respond to the first preferred tuberculosis drugs. XDR TB doesn't respond to the first and second preferred drug treatments.

Speaker's case also garnered instant attention when the CDC ordered him into isolation for medical treatment and alerted the public about his travels so that passengers on his transatlantic flights could get TB tests.

If tuberculosis is contagious, why don't Speaker's wife or friends have tuberculosis?

"It sounds like he's probably somebody who was in a pretty early state of TB," says Hamilton, cautioning that she isn't personally familiar with Speaker's case.

"He wasn't horribly sick because he felt like going on his honeymoon and he was what's called 'smear negative.' In those situations, often people aren't very infectious," says Hamilton.

What is "smear-negative" TB?

"What that means is that when he coughed up a specimen to give to the doctors to test for TB, the laboratory looked under the microscope [and] they didn't see any TB bacteria. It was only when [the sample] was cultured that then they figured out, 'Oh, there really is TB here' and then it took some weeks to figure out it was drug resistant," says Hamilton.

In contrast, smear-positive TB patients "have so much TB in their lungs that when the laboratory looks directly into the microscope, they can see the bacteria right there. Those people tend to be a lot more infectious or contagious to others than someone who really has disease but doesn't yet have enough built up that they're really coughing out a whole lot at a time."

When TB bacteria keep growing, eventually "you can see it under a microscope, and that's associated with easily infecting other people," Hamilton says.