Researchers from the U.S. Centers for Disease Control and Prevention, tested samples from more than 1,200 TB patients from eight countries who were classified as having multi-drug resistant tuberculosis. The infection was resistant to one or both of the older, first-line drugs, rifampacin and isoniazid.
But investigators found 6.7 percent of the patients were infected with extensively drug resistant TB, known as XDR. The XDR-TB patients did not respond to a regimen that included the first-line treatments, and quinolone drugs and newer injectable drugs.
Investigator Tracy Dalton, of the CDC’s Division of TB Elimination, led the study. “So, what this presents is a really worrying trend in increasing XDR in the world,” she said.
Before the study, the World Health Organization estimated that just more than five percent of all resistant cases of TB were XDR.
Dalton says resistance to at least one newer anti-TB drug was detected in 44 percent of the patients, ranging from 33 percent in Thailand to more than 60 percent in Latvia. Other countries in the study were Estonia, the Philippines, Russia, South Africa, South Korea and Peru.
Dalton says the increased availability of newer tuberculosis drugs increases the likelihood they are not taken as prescribed, which causes the TB bacterium to become less sensitive to the stronger drugs. Dalton says the biggest predictor of whether someone in the study was infected with XDR TB was whether they had previously been treated for tuberculosis.
“What we found in many of these sites is that there was resistance to all of these second-line drugs. And we need more drugs to be available, and that is a high priority in TB control right now,” Dalton said.
Dalton says it is critical to take immediate steps to contain the spread of extensively drug resistant tuberculosis, including building more and better lab facilities to test for TB.
“There is a lot going on in molecular testing of drug resistance, which would be a rapid diagnosis of these patients,” Dalton said.
Since Dalton’s study, the WHO has revised its estimate of the number of global XDR-TB cases upward, to 10 percent of all patients diagnosed with drug-resistant tuberculosis.
A study on extensively drug -resistant tuberculosis by Tracy Dalton and colleagues at the Centers for Disease Control is published in the journal The Lancet.
