A standard and inexpensive tuberculosis treatment regimen cut the overall TB rate in half and lowered the rate of drug-resistant cases even more dramatically in a remote Mexican health district with a high prevalence of the disease. “This shows what basic TB control can accomplish,” said Maria de Lourdes García García, a Howard Hughes Medical Institute international research scholar who led the Mexican study.
To learn more about TB transmission in less developed countries, García García and colleagues from the National Institutes of Mexico and Stanford University launched a five-year study in the Orizaba Health Jurisdiction, four hours by bus southeast of Mexico City. The district, which has a higher rate of TB than Mexico as a whole, encompasses five mostly urban communities in an industrialized valley and surrounding rural mountains.
Supported by HHMI, the U.S. National Institutes of Health, and the Wellcome Trust, the study used modern molecular epidemiologic approaches, in addition to screenings, clinical assessment of people reporting symptoms, supervised treatment, and follow-up, to explore a global health problem.
At the outset, 22 percent of previously untreated patients with pulmonary TB were carrying drug-resistant strains, and 6.7 percent had multiple-drug resistance. By the study's final year, only 7.8 percent of new TB patients carried drug-resistant strains, and there were no cases of multiple-drug resistant TB.
The researchers report their findings in the April 2, 2005 issue of the British medical journal The Lancet. A commentary by Marcos Espinal, executive secretary of the World Health Organization's Stop TB Partnership, appears in the same issue.
People with TB must take four standard drugs daily for six months. They may begin to feel better after a month, which tends to lead them to skip doses, but if they stop taking the drugs for any reason, the drugs may become ineffective and multi-drug resistant TB may result. Multi-drug resistance refers to resistance to two of the most powerful anti-TB drugs, rifampicin and isoniazid. Overcoming this drug resistance is a major goal of public health programs fighting TB.
When García García's study began in 1995, regional health officials in Mexico had begun to upgrade their TB treatment program to a World Health Organization model called directly observed therapy (DOTS). The five-pronged strategy of DOTS includes political commitment to the eradication of TB, case detection by sputum microscopy, supervised administration of drugs for at least the first two months of treatment, an uninterrupted supply of all essential drugs, and a rigorous assessment of treatment and outcomes.
The results of the Mexican study “strongly suggest that DOTS reduces transmission of resistant strains by curing cases of TB that otherwise could become multi-drug resistant if they are not properly treated,” said Marcos Espinal, executive secretary of the Stop TB Partnership at the World Health Organization. “This study shows that DOTS is needed to control multi-drug resistance. Without DOTS, measures directed to multi-drug-resistant TB will not work.”