Isoniazid Mono-Resistant Tuberculosis: Impact on Treatment Outcome and Survival of Pulmonary Tuberculosis Patients in Southern Mexico 1995-2010.

Background: Isoniazid mono-resistance (IMR) is the most common form of mono-resistance; its world prevalence is estimated to range between 0.0 to 9.5% globally. There is no consensus on how these patients should be treated. Objective: To describe the impact of IMR tuberculosis (TB) on treatment outcome and survival among pulmonary TB patients treated under programmatic conditions in Orizaba, Veracruz, Mexico. Materials and Methods: We conducted a prospective cohort study of pulmonary TB patients in Southern Mexico. From 1995 to 2010 patients with acid-fast bacilli or culture proven Mycobacterium tuberculosis in sputum samples underwent epidemiological, clinical and microbiological evaluation. We included patients who harbored isoniazid mono-resistant (IMR) strains and patients with strains susceptible to isoniazid, rifampicin, ethambutol and streptomycin. All patients were treated following Mexican TB Program guidelines. We performed annual follow-up to ascertain treatment outcome, recurrence, relapse and mortality. Results: Between 1995 and 2010 1,243 patients with pulmonary TB were recruited; 902/1,243 (72.57%) had drug susceptibility testing; 716 (79.38%) harbored pan-susceptible and 88 (9.75%) IMR strains. Having any contact with a person with TB (adjusted odds ratio (aOR)) 1.85, 95% Confidence interval (CI) 1.15–2.96) and homelessness (adjusted odds ratio (aOR) 2.76, 95% CI 1.08–6.99) were associated with IMR. IMR patients had a higher probability of failure (adjusted hazard ratio (HR) 12.35, 95% CI 3.38–45.15) and death due to TB among HIV negative patients (aHR 3.30. 95% CI 1.00–10.84). All the models were adjusted for socio-demographic and clinical variables. Conclusions: The results from our study provide evidence that the standardized treatment schedule with first line drugs in new and previously treated cases with pulmonary TB and IMR produces a high frequency of treatment failure and death due to tuberculosis. We recommend re-evaluating the optimal schedule for patients harboring IMR. It is necessary to strengthen scientific research for the evaluation of alternative treatment schedules in similar settings. [ABSTRACT FROM AUTHOR]