PREVALENCE OF MULTIPLE-DRUG RESISTANT Mycobacterium tuberculosis (MDR-TB) IN PULMONARY TUBERCULOSIS PATIENTS DETECTED BY THE MICROSCOPIC-OBSERVATION DRUG SUSCEPTIBILITY (MODS) ASSAY IN CALABAR, NIGERIA

Abstract

Background: Tuberculosis affects one third of the worlds’ population and caused more than 4.7 million deaths globally in the last 3 years. The emergence and spread of multidrug resistant strains of Mycobacterium tuberculosis (MDR-TB) has compounded the problem. In Nigeria, one of the highest burden countries, diagnosis of tuberculosis has remained dependent on smear microscopy which has been shown to be of limited diagnostic ability. Drug susceptibility testing is also rarely available. Aim: I evaluated the feasibility of the new rapid method of diagnosis and drug susceptibility testing of tuberculosis, the Microscopic Observation Drug Susceptibility (MODS) assay and the epidemiology and molecular characteristics of M. tuberculosis in Calabar, Nigeria. Methods: The study was a prospective cross sectional study. Three sputum specimens were submitted by tuberculosis suspects for smear microscopy. The early morning specimen was retrieved and cultured by MODS assay. The genotypes of the culture isolates were determined by spoligotyping. Results: A total of 50(31.2%) of 160 enrolled patients were positive for M. tuberculosis. There was a statistically significant advantage (P=0.019) of MODS over smear microscopy which missed 7(14.0%) of the diagnosis. Mean time of diagnosis with MODS was 8.4 (SD2.5) days (range of 5-13 days). MODS result was available in 9(18.4%) of patients in 5 days. Modal duration was 7days (17(34.7%)). Turnaround time for smear microscopy in the centers was 3 days. The cost per specimen of MODS was about ₦530.00. Two (4.1%) of patients had MDR-TB strains while 1(2.0%) was isoniazid monoresistant. They was a statistically significant negative correlation between tuberculosis and age (P=0.019) with a cluster between ages 20-39 years. The only risk factor observed for carriage of a drug resistant strain was previous tuberculosis treatment (P=0.005). Thirteen different spoligotypes belonging to 7 lineages were identified. The Latin America Meditterenean (LAM) (39.5%), T (23.3%) and Haarlem (18.6%) lineages were predominant. While LAM10(CAM) was the most prevalent spoligotype and it included all the drug resistant strains. Conclusion: The MODS technique is a rapid and convenient method of tuberculosis and multidrug resistant tuberculosis detection. It is feasible in Nigeria and its wide scale application will scale up tuberculosis control efforts in the country. More studies on the genetic fingerprints of the M. tuberculosis complex are necessary to better understand the spread of the disease, geographic variations and possible clonal expansions of MDR-TB strains.