Changing Trends in the Susceptibility Pattern of Mycobacterium tuberculosisOver a Decade from a Tertiary Care DOTS Centre Delhi

Study Background: Drug resistance in Mycobacterium tuberculosis is a serious problem all over the world. One of the major factors contributing to drug resistance is delayed detection of drug-resistant isolates, which ultimately leads to delay in initiation of effective chemotherapy. An appropriate modification of treatment regimens, depending upon the susceptibility pattern of Mycobacterium isolates is the keystone for successful treatment of drug-resistant tuberculosis. Material and methods: The study was done to check the susceptibility pattern of both pulmonary and extrapulmonary isolates of Mycobacterium tuberculosis during Aug 2009 - Jun 2012, Phase II (35 month period) and compared it with our previous data of same duration (Aug 2002-Jun 2005, Phase I), to determine the burden of drug resistance in the current situation and to look for the change in resistance pattern over a decade. A total of 154 culture-confirmed Mycobacterium tuberculosis isolates (pulmonary-36, extra-pulmonary-118) were screened for their susceptibility pattern. Drug susceptibility testing was performed by an automated Bac T-Alert 3D, using ‘SIRE’ kit’ provided with Bact Alert 3D system (Biomereiux Pvt Ltd). Result: Current study demonstrated increased drug resistance for streptomycin, isoniazid, rifampicin and ethambutol as 8/36 (22.2%), 23/36 (63.8%), 6/36 (16.6%) and 21/36 (33.3%) respectively in the pulmonary isolates and 39/118 (33%), 71/118 (60.1%), 16/118 (13.5%) and 60/118 (50.8%) among the extra-pulmonary isolates. A significant increase in resistance (p value=0.0001) was observed for streptomycin in current phase as compared with the earlier phase of study while resistance to rifampicin was decreased in pulmonary isolates. However, resistance to streptomycin, isoniazid and ethambutol were significantly increased (p value=0.0001) among extrapulmonary isolates. Conclusion: Resistance to streptomycin has increased at an alarming rate in pulmonary tuberculosis (TB). However, resistance to isoniazid and rifampicin has stabilized over time, this could possibly imply adequacy of DOTS coverage in cases of pulmonary TB. This situation in patients with extra-pulmonary TB is more alarming as this data reveals a dramatic increase of resistance to isoniazid and other first-line agents. The “hidden reservoir” of resistance in extra-pulmonary patients may downgrade the efficacy of the DOTS program in the future.