Distribution of drug-resistant tuberculosis in Zambia, 2008-2011

Abstract

Background: Mycobacterium tuberculosis is treated with four drugs: Isoniazid (INH), Rifampicin (RIF), Pyrazinamide (PZA) and Ethambutol (E). The emergence of drug resistant strains of Mycobacterium tuberculosis threatens the success of national tuberculosis (TB) programmes. Zambia has recorded a reduction in the notification rates of all forms of tuberculosis over the years but the burden of multiple drug resistant TB (MDR TB) which is resistance to the drugs isoniazid and rifampicin, with or without resistance to other drugs, is not well defined. This study aimed to describe the distribution of drug resistant TB in Zambia over the four year period 2008-11. Methodology: This study was a retrospective review of national tuberculosis sputum analysis data from the Chest Disease Laboratories and the Topical Diseases Research Centre for the period 1st January 2008 to 31st December 2011. The variables in the anonymised database were: location of case (province), age, gender, and drug sensitivity test (DST) result to the four first-line anti-TB drugs. Analysis of the data was performed using STATA 11.0. Results: Of the sputum specimens from 7,579 cases collectively received at the two laboratories, 811 cases had complete DST results. From these 811 cases, 404 (49.8%) were susceptible to all 4 drugs, and 407 (50.2%) had resistance to one or more of the anti-TB drugs. Mono-resistance was most common to isoniazid (INH) (5.3%) and streptomycin (SM) (3.3%). MDR TB was found in 256 (31.6%) of the cases. Over the four years under investigation, MDR TB cases increased from 24.2% in 2008 to 30.9% in 2011. Analysis of MDR TB by gender, location and age showed more cases in males than females (57% vs. 37.9%); more cases in Lusaka (49.3%) and the Copperbelt (30.1%) provinces; and the highest proportion of cases in the 35-49 years age group (31.3%). Three MDR TB cases were recorded for the age group <20 (of 25 cases tested). Being age <20 years was less likely to be associated with MDR TB (p=0.0337). However, MDR TB was not statistically significantly associated with gender or location. Conclusions: The study showed significant proportions of mono and MDR-TB among the study sample that included drug sensitivity test results on all four anti-TB drugs. Drug resistant TB in Zambia will continue to be a challenge to management and control of TB if not properly managed. Studies on treatment outcomes of mono resistant TB patients need to be performed to inform the current treatment regimens.