"In countries with low prevalence of initial multi-drug resistance, the standardized treatment regimens for new case appear to be adequate," writes Dr. Dick Menzies, M.D., lead author of the study and director of the respiratory division at McGill University.
"However, in countries where the prevalence of initial drug resistance exceeds three percent, we believe it is urgent to strengthen capacity to perform drug sensitivity testing, or to re-evaluate these standard treatment regimens, given the unacceptably high rates of failure and relapse," he writes in his study report, appearing in the American Journal of Respiratory and Critical Care Medicine.
Dr. Menzies highlights the fact that MDR-TB was much less common when the current public health strategies were conceived.
"We hypothesized that, in countries using standardized initial and retreatment regimens, the proportion of patients with poor treatment outcomes would be correlated with prevalence of initial and acquired multi-drug resistance," he writes.
For their study, Dr. Menzies and his colleagues reviewed the WHO's data from 2003 and 2004 for a total of 155 countries, 121 of which reported at least 250 cases annually.
The researchers assessed dropout, failure, relapse, and death rates with initial treatment, as well as dropout, failure and death rates for re-treatment.
They analysed all the rates with respect to the prevalence of MDR-TB in each country.
Dr. Menzies says that his group's analysis showed that rates of failed treatment were dramatically higher with increasing prevalence of MDR-TB.
After accounting for age, HIV prevalence, per capita income and treatment regimen, for every one-percent increase in MDR TB prevalence, the researchers saw a 0.30 percent rise in treatment failure among new cases, a 1.1 percent increase in failure rate among re-treatment cases, and a one percent increase in relapse.
"This is striking evidence that MDR-TB is directly linked to the increased failure rates of our current treatment regimens," says Dr. Menzies.
Overall, the proportion of patients requiring re-treatment nearly doubled between countries with low and high prevalence of MDR-TB, from 11.9 percent in countries with initial MDR prevalence of less than one percent, to 21.4 percent in countries with MDR prevalence of more than three percent.
"In the short term, the higher the failure and relapse rates mean greater morbidity and mortality for patients, with greater social and economic harm for their families and communities. In the long term, these standardized regimens may be contributing to amplification of multi-drug resistance in these countries," writes Dr. Menzies.
Based on their observations, the researchers came to the conclusion that by continuing to use the existing treatment regimens, public health officials may be unwittingly increasing the problem of drug resistance and multiplying the problem for other future patients.
"Unless those with the responsibility to boost control and research efforts increase their commitments and their financial investments by several fold, we may never see elimination of this major scourge in the decades to come," writes Dr. Marcos Espinal and Dr. Mario C. Raviglione, both of the WHO, in an accompanying editorial in the same issue of the journal.