Drug resistance of mycobacterium tuberculosis in Orizaba, Veracruz. Implications for the tuberculosis prevention and control program.

Background. Tuberculosis, declared a global emergency by the World Health O rganization, continues to be an important public health problem in Mexico, included in the first twenty causes of death. Objective. To know the impact of drug resistance of Mycobacterium tuberculosis on treatment outcome, nee d of re-treatment and mortality in a cohort of patients with pulmonary tube rculosis receiving directly observed therapy, short course (DOTS). Methods. We conducted a population-based study in a suburban region in Southern Mex ico. People who had been coughing for more than two weeks underwent sputum acid-fast bacilli smear. Patients with a positive smear were recruited and underwent clinical exam, chest X-ray, HIV testing, and sputum cultures. Ide ntification, drug susceptibility testing and restriction fragment length po lymorphism analysis (RFLP) were performed in all isolates. Patients were fo llowed every 12 months for new episodes of tuberculosis and vital status. P atients were referred for clinical care to the local program of tuberculosi s. Deaths were corroborated with death certificates. Informed consent was o btained from participants. Results. Between March 1995 and February 1999, t uberculosis was diagnosed in 371 patients who were followed for an average of 32 months. M. tuberculosis was cultured from 316 patients; resistance to any drug occurred in 25.0% of isolates (primary 18.8%, acquired 49.2%); on ly to isoniazid in 6.8% (primary 7.3%, acquired 4.8%); to isoniazid and rif ampin in 6.2% (primary 1.6%, acquired 23.8%). Patients with drug resistance had a higher probability of treatment failure (OR = 16.9, CI 95% 4.5-63.0) and patients with MDR strains had a higher probability of need of re-treat ment (RR = 24.4, CI 95% 8.8-67.6), and of death (RR = 4.0, CI 95% 1.5-10.7) . Additional variables were found to be associated with subsequent episodes of disease and mortality: Cocaine use, chronic disease, type of radiologic al lesions, HIV co-infection, non-compliance and treatment delay, as well a s RFLP clustering. Conclusions. In this study, we observed that drug resist ance showed a severe impact on the outcome and survival; drug-resistance wa s the most significant factor for these negative outcomes; DOTS may not be sufficient in areas where drug resistance is considerable, and patient foll owup for longer periods of time, as compared to evaluation at the end of tr eatment, provides additional information which is useful for prevention and control programs.