A study of more than 1,200 adults worldwide reveals that the prevalence of tuberculosis (TB) strains that are resistant to both first- and second-line treatments is higher than previously realized. Extensively drug-resistant tuberculosis strains were detected in 6.4 percent of all samples analyzed, according to the results of the study, published online yesterday (August 29) in The Lancet, with some countries, such as South Korea, having a prevalence of around 15 percent.
Strains resistant to second-line treatments—those administered after initial treatments have failed—were found in 44 percent of the patients, with some countries such as Latvia having patient populations where as high as 62 percent of infections were resistant.
“Most international recommendations for TB control have been developed for MDR [multidrug-resistant] TB prevalence of up to around 5 percent,” Sven Hoffner, Associate Professor at the Swedish Institute for Communicable Disease Control, wrote in an accompanying comment. “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.”
Multidrug-resistant strains are classified as such if they resist treatment with at least two common first-line drugs, such as isoniazid and rifampicin, whereas to be categorized as “extensively drug-resistant,” tuberculosis strains must also be resistant to a fluoroquinolone and a second-line injectable drug.
“Treatment options for patients with extensively drug-resistant tuberculosis are limited, expensive, and toxic,” Tom Evans, chief scientific officer of Aeras, a non-profit organization dedicated to the development of TB vaccines, said in a statement in response to the Lancet study. “In the United States, MDR-TB treatment can cost $250,000 or more per patient, and in most low-middle income countries, costs can be catastrophic to both the health system and the impacted family.”