Risk of XDR-TB in the U.S. low, expert says

According to the World Health Organization, the reported strain of tuberculosis that caused 12 cases of totally drug-resistant tuberculosis in India in January is more accurately described as extensively drug-resistant TB.

The WHO said that the alleged superbug is severe, but it does not meet the definition of TDR-TB. XDR-TB is resistant to at least four of the major anti-TB drugs and may be resistant to any of the fluoroquinolones and to any one of three injectable second-line drugs, AAFP News Now reports.

"According to the WHO, XDR-TB takes substantially longer to treat than ordinary (drug-susceptible) TB, and requires the use of second-line anti-TB drugs, which are more expensive and have more side effects than the first-line drugs used for drug-susceptible TB," Paul Hunter, the associate medical director for the city of Milwaukee Health Department, said, according to AAFP News Now. "TDR basically means you're using everything available at your site and it is ineffective, but that term doesn't mean anything (in this case) because what is available in India is different from what we have available here."

Hunter said that the chances that a virtually untreatable form of TB would spread to the United States are low because of immigration screening. He said that the bigger issue for physicians in the U.S. is latent TB infection, which is when someone has been exposed to TB but does not have symptoms and cannot transmit the bacteria to others. Approximately 10 percent of people with LTBI will develop active TB.

"You have to make sure you don't treat active disease using a single medication or the wrong combination of medications, because that is what leads to drug-resistant TB," Hunter said, according to AAFP News Now. "If you do it wrong, you're going to push your patients toward drug resistance."