Lancet Infectious Diseases examines spread of XDR-TB

Jun 24 2009

The journal Lancet Infectious Diseases examines the worldwide spread of extensively drug-resistant tuberculosis (XDR-TB). Currently, about 500,000 of the 9 million new cases of TB that are identified each year are strains of XDR-TB. "Drug resistance is largely man-made - it is vitally important to review antibiotic treatment strategies and to ensure the Stop TB Strategy is fully applied to prevent further selection of drug-resistant mutants," Leonard Amaral of Universidade Nova de Lisboa said.

XDR-TB - "which is resistant to isoniazid and rifampicin (two first-line TB drugs), any fluoroquinolone, and at least one of the three injectable second-line drugs: amikacin, kanamycin, and capreomycin" - is "widespread" in Europe and the Middle East, according to the journal.

Data from the CDC shows the following countries have the highest percentage of XDR-TB among multi-drug resistant cases (MDR-TB): Azerbaijan (12.8 percent), Ukraine (15 percent) and Estonia (23.7 percent). In Western Europe, Portugal has the highest number of XDR-TB cases with more than 50 percent of the country's MDR-TB cases being XDR-TB. Determining drug-resistant TB rates in other regions is difficult, according to the Lancet. Philip LoBue of the CDC said, "data from many parts of the world are limited or completely unavailable because of lack of access to drug-susceptibility testing."

Using conventional methods, the diagnosis of XDR-TB takes between six and eight weeks, "but more rapid molecular tests are in development," the journal writes. LoBue said, "Research that leads to new rapid diagnostics could have a great impact and a database of TB drug mutations could contribute significantly to this." The article notes that researchers from the Harvard School of Public Health recently created such a database.

William Bishai of the Johns Hopkins School of Medicine highlighted the need for faster tests that are also usable at the location of treatment. "Diagnostics based on breath tests or fingersticks would be ideal - a recent Médecins Sans Frontières expert panel recommended that we aim for diagnostics that can be carried in a backpack, give same-day results, and function by battery for 24 hours," Bishai said.

New drugs with "shorter treatment times are also needed," the Lancet writes. Although there are some "promising new" experimental drugs, "licensing and approval could take years yet, and any improvement in survival rates in the foreseeable future is unlikely," according to the journal (Senior, Lancet Infectious diseases, 7/09).