A new study by the Centers for Disease Control and Prevention might change the way doctors treat latent tuberculosis, the noninfectious type of the disease found in about 11 million Americans.
The study found that an easier, shorter treatment for latent tuberculosis may prevent those cases from becoming active. Active tuberculosis produces symptoms and is highly contagious.
MPR medical analyst Dr. Jon Hallberg discussed the study's implications Tuesday on All Things Considered with host Tom Crann. Hallberg is a physician in family medicine at the University of Minnesota and director of the Mill City Clinic in Minneapolis.
Tom Crann: First, tell us the difference between tuberculosis and latent TB.
Dr. Jon Hallberg: With latent TB, a person has been exposed to tuberculosis, a bacterial infection, a microbe, but it's simply not manifesting. It's being held in check by the immune system. And many, many more people in the world have latent TB than active TB.
Crann: So how prevalent, for example, in the U.S. is latent TB?
Hallberg: They think something like 4 percent of the U.S. population has it. That'd be about 11 million people. But by contrast, worldwide something like two billion have latent TB, and something like three million people die of it every year. So if unchecked, if untreated, TB is very much a killer in the world.
Crann: Without symptoms, how do people know if they actually are walking around with latent TB?
Hallberg: They won't, unless they get tested. Many people are familiar with what's called the Mantoux test or a PPD test. ... there's a test where a little blob of fluid is put underneath the skin on the forearm, and then you watch it for two to three days and see if you get this hard induration. And if you do, it means that you've got antibodies against it.
Crann: How common is this to come across in a clinic setting? You mentioned that health care workers are screened for this. How often do you see it?
Hallberg: In my world, I don't see it very often. I've got a clinic population that just doesn't have a lot of TB, at least not that I'm aware of. But I do see [the test] a lot, because I've got a lot of patients who are physicians and nurses and people in health care.
Crann: When it comes to the treatment, this is an antibiotic that's given? TB is a bacterial infection?
Hallberg: That's right. And for years, if you have latent TB, the plan has been to give you once-a-day INH, isoniazid, an old, old medication, super cheap, but you have to take it every single day for nine months. And for many people, it's the only drug they're on, and so it's very hard for people to actually complete that nine-month course.
Crann: So, what happens? People just drop off, stop taking it?
Hallberg: They do, and then potentially you're going to create some resistance. We've heard a lot about multi-drug resistant TB around the world, and so you start putting yourself at risk if you don't complete the treatment.
Crann: This study, what does it find?
Hallberg: What they did is they simply gave more of the INH medication, and they coupled it with another one called rifapentine, which came out in 1965 [and was] approved in 1998. And the combination of the two, taken once a week for 12 weeks or three months, so 12 doses, was as effective as 270 doses of the traditional INH. Anytime you can take something once a week for a shorter period of time, you're going to have, what they found, is much more compliance with completing that course.
Crann: Are these findings enough, as far as you're concerned, to change the way latent TB is treated?
Hallberg: It's very clear that the CDC is already reevaluating their guidelines for treatment. It's pretty rare that you see that, but this is a really good study. It was conducted for 10 years, 8,000 people. I think it is going to lead to a policy change.
Crann: TB is off a lot of people's radar certainly here in the U.S. Not true around the world, right?
Hallberg: That's right. When you couple TB with something like HIV, it's devastating. And in fact, as people know, you don't really die of HIV/AIDS per se. You die of complications because your immune system isn't working, and TB is right at the top of the list of what ultimately takes people's lives.
Crann: What implications does this have for countries with a higher prevalence of TB and HIV/AIDS?
Hallberg: It's tricky to know at this point, because this study excluded anyone who had HIV because there's some problems with one of the drugs with the antiretrovirals that people might be on if they have HIV. So they've really got to almost go back to the drawing board and think about that.
The better hope, I think for this, is that because we have a relatively low rate in the United States, we might be able to essentially eradicate it from this country. That's certainly the goal, that's the hope.
(Interview edited and transcribed by MPR reporter Madeleine Baran)