Does Latent TB Need Treatment?

I had a negative tuberculosis skin test a year ago, and this year it was positive. My chest x-ray showed no active tuberculosis. Are the 9 months of drug treatment recommended for latent disease really necessary? What can I do to stay healthy? I’m a 44-year-old female under lots of stress.

– August 16, 2011

Tuberculosis (TB) is caused by a germ called Mycobacterium tuberculosis. The disease spreads from person to person when someone who is actively infected coughs or sneezes and another person breathes in contaminated droplets. If you have latent TB – that is, tests show that you’ve been infected although you’re not sick – you can’t spread the disease to others. The only way you would know that you are living with latent tuberculosis is via testing: those infected usually will have a positive reaction to the tuberculin skin test. This involves injection of a substance called PPD tuberculin under the skin of your inside forearm. Within 48 to 72 hours you must be checked for swelling at the injection site. If there’s a hard, red lump, you’re probably infected. The size of the lump determines how significant this reaction is.

If you have latent TB, you do need treatment to prevent the disease from becoming active, endangering your own health and that of others. The currently recommended treatment for latent TB is nine months of the drug isoniazid taken by mouth. However, results of a 10-year international clinical trial involving more than 8,000 participants have shown that three months of treatment with isoniazid plus another drug, rifapentine, works just as well. The findings were reported in May, 2011, at the American Thoracic Society International conference.

A big advantage seen with the shorter treatment is that more patients completed the entire course – 82 percent vs. 69 percent of those on the nine-month regimen in the trial. This is a big improvement over the less-than-50-percent completion rate with current treatment. Some of the improvement in the study was attributed to the fact that participants were medically supervised rather than left to take the drugs on their own. However, the Centers for Disease Control, which sponsored the trial, will develop guidelines for the use of the three-month treatment program. They should be available later this year.

Side effects of isoniazid can include diarrhea and vision problems, but more importantly, both isoniazid and rifapentine can cause liver damage. Because of this risk, you may need periodic lab tests during treatment to check your liver function. An excellent way to protect your liver (that your physician may not know) is to take milk thistle (Silybum marianum) along with the drugs – 175 milligrams of an extract standardized to 80 percent silymarin three times a day as long as you are on them. It’s important to take the full course of treatment.

Andrew Weil, M.D.

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