Tuberculosis treatment failure and drug resistance-same strain or reinfection?

Tuberculosis patients may have Mycobacterium tuberculosis in their sputum a t the end of treatment, and may show new drug resistance, due to either ina dequate treatment of the original episode or reinfection with a new strain during therapy. In a cohort study of mineworkers with tuberculosis in South Africa, 57 of 438 patients had positive sputum cultures 6 months after rec ruitment in 1995. Of the 31 patients who initially had fully sensitive stra ins, 3 developed multidrug resistance (MDR) and 3 single-drug resistance (S DR). Of the 6 who started with SDR, 3 became MDR. HIV infection was nor ass ociated with drug resistance at enrolment or 6 months later. We compared pa irs of DNA fingerprints from isolates of M. tuberculosis at recruitment and 6 months later in the 48 patients for whom we had both available. In 45, t he pairs were identical. In 1 patient, although both isolates were fully se nsitive, the later fingerprint had 1 less band (transposition). In 2 pairs, the fingerprint patterns were completely different: one seemed to be the r esult of laboratory error and the other was a true reinfection with an MDR strain. Despite a high risk of infection, with a moderate proportion of bac kground drug-resistant strains (11% SDR, 6% MDR), reinfection is not a comm on cause of treatment failure or drug resistance at 6 months.