Drug resistance of Mycobacterium tuberculosis in Karachi, Pakistan

We determined the primary and secondary resistance of isolates of M. tuberculosis to the standard antituberculous drugs in Karachi (Pakistan). Primary resistance to one or more anti-tuberculous drugs was found in 17% of 123 isolates of M. tuberculosis (obtained from patients with no history of previous treatment for tuberculosis). Secondary resistance was found in 36% of 33 isolates (obtained from individuals who had received anti-tuberculous treatment in the past). The drug to which organisms were most commonly resistant was isoniazid (11% primary resistance, 30% secondary resistance). Fifteen per cent of isolates obtained from previously-studied patients showed secondary resistance to rifampicin. We discuss the importance of these findings for tuberculosis treatment and control.