A large international study published Thursday shows rates of both multidrug-resistant TB (MDR TB) and extensively drug-resistant TB (XDR TB) in Africa, Asia, Europe, and Latin America are much higher than previously thought.
MDR TB is resistant to at least two first-line treatments - isoniazid and rifampicin - and XDR TB is resistant to these two as well as fluoroquinolone and a second-line injectable antibiotic. The rise of drug-resistant TB is partly due to patients failing to complete the lengthy six-month regimen of powerful antibiotics used to treat regular TB.
Treatment for drug-resistant TB can cost 200 times more than regular TB and take up to two years to complete, said Tom Evans, chief scientific officer at Aeras, a nonprofit working to develop new TB vaccines. Medical options for XDR TB patients, he said, are “limited, expensive, and toxic.”
CDC’s Tracy Dalton, who led the study, said the spread of drug-resistant TB is “particularly worrisome” in areas with limited health care resources and poor access to effective drugs. So far, she said, XDR TB has been reported in 77 countries worldwide. “As more individuals are diagnosed with, and treated for, drug-resistant TB, more resistance to second-line drugs is expected to emerge,” she noted.
The study found resistance to at least one second-line TB drug in nearly 44 percent of patients overall, ranging from 33 percent in Thailand to 62 percent in Latvia.
In about one-fifth of cases, resistance was seen to at least one second-line injectable drug, ranging from 2 percent in the Philippines to 47 percent in Latvia. XDR TB was detected in 6.7 percent of patients overall. XDR TB rates in South Korea (15.2 percent) and Russia (11.3 percent) were more than double the World Health Organization’s global estimate of 5.4 percent.
[PNU editor’s note: The study, “Prevalence of and Risk Factors for Resistance to Second-Line Drugs in People with Multidrug-Resistant Tuberculosis in Eight Countries: A Prospective Cohort Study,” was published in The Lancet (2012;doi:10.1016/S0140-6736(12)60734-X).]