MDR-TB, XDR-TB more widespread than previously believed, study shows

In a study published on Wednesday in the Lancet, researchers from the Centers for Disease Control and Prevention found that "[a]mong 1,278 patients who were resistant to two or more first-line tuberculosis drugs in Estonia, Latvia, Peru, Philippines, Russia, South Africa, South Korea and Thailand, 43.7 percent showed resistance to at least one second-line drug," which "suggest[s] the deadly disease may become 'virtually untreatable,'" according to the study, Bloomberg Businessweek reports (Kitamura/Narayan, 8/29). "In about a fifth of cases, they found resistance to at least one second-line injectable [versus oral] drug," according to Reuters, which states "[t]his ranged from two percent in the Philippines to 47 percent in Latvia." Overall, 6.7 percent of patients had extensively drug-resistant TB (XDR-TB), meaning patients are resistant to the first-line drugs isoniazid and rifampicin as well as drugs in the fluoroquinolone antibiotic class and a second-line injectable antibiotic, Reuters adds, noting "[r]ates in South Korea, at 15.2 percent, and Russia at 11.3 percent, were more than twice the WHO's global estimate of 5.4 percent at that time" (Kelland, 8/30).

"In the study, the authors wrote that their findings showed 'previous treatment with second-line drugs was consistently the strongest risk factor for resistance to these drugs, which increased the risk of XDR tuberculosis by more than four times,'" CNN's "The Chart" blog reports. But Karin Weyer of the WHO's Stop TB Partnership "cautioned that only data from Estonia and Latvia were representative of what was happening at the country level" because data from the other countries was not population-based but collected from smaller geographical areas, the blog notes (Hagan, 8/29). "She saw the study as a wake-up call, however," according to the Guardian, which adds, "'If you don't manage MDR properly, you end up with XDR,' she said." In an accompanying Lancet commentary, Sven Hoffner of the Swedish Institute for Communicable Disease Control "said new information on the spread of drug-resistant TB was urgently needed," the newspaper states. He wrote, "Most international recommendations for TB control have been developed for MDR-TB prevalence of up to around five percent. Yet now we face prevalence up to 10 times higher in some places, where almost half of the patients with infectious disease are transmitting MDR strains," the newspaper notes (Boseley, 8/30).