Latent TB treatment a greater risk to older adults

Older adults treated for an inactive tuberculosis infection may be at increased risk of suffering liver damage from the medication, a study published Monday suggests.

Canadian researchers found that among all Quebec residents treated for so-called latent tuberculosis (TB) over six years, those older than 65 were more likely to be hospitalized for liver damage.

Overall, 2.6 percent of the treated older adults were hospitalized, compared to 0.2 percent of those in the same age group who were not treated for latent TB, the authors report in the Canadian Medical Association Journal.

The findings, researchers say, suggest that doctors need to carefully weigh the pros and cons of treating latent TB in people older than 65.

TB is a serious, potentially fatal bacterial infection that primarily attacks the lungs. The bacteria, called Mycobacterium tuberculosis, are spread through the air from person to person.

In most people, the immune system is able to suppress the bacteria from growing and spreading; these individuals do not become sick and they cannot spread the infection to anyone else. The TB bacteria do, however, remain in the body in an inactive state - what doctors call a latent infection.

In some cases, latent TB can become active. At particular risk are people with significantly weakened immune systems - from HIV, for instance, or certain immune-suppressing drugs used to treat cancer or autoimmune disorders like rheumatoid arthritis and Crohn's disease.

People at high risk of developing an active infection may be offered TB treatment, which usually means six to nine months of a drug called isoniazid.

Liver damage is a known side effect of the drug. But until now, no large studies had looked at how often latent TB treatment causes serious liver problems in the general population.

"The main goal of this study was to quantify the risk," said lead researcher Dr. Benjamin A. Smith, of McGill University in Montreal. "We were able to get a real-world picture, so we can give meaningful information to patients."

According to Smith, the findings suggest that with older adults, the risk of latent TB reactivation needs to be carefully weighed against the risk of liver damage from treatment.

"By definition, people with latent TB are well," Smith said. "So you want to try to be sure that the benefits outweigh the risks before you treat."

The picture can get complex, he noted. Along with the main risk factors for TB reactivation - like chemotherapy and HIV infection - there are some other conditions that can contribute. Diabetes and advanced kidney disease, for example, have effects on the immune system that could raise the odds of the TB bacteria becoming active.

Those conditions, which are quite common in the elderly, are relatively minor risk factors for TB reactivation, however.