UNEXPECTEDLY HIGH-STRAIN DIVERSITY OF MYCOBACTERIUM-TUBERCULOSIS IN AHIGH-INCIDENCE COMMUNITY

Objective. To characterise Mycobacterium tuberculosis strains present in a community experiencing an epidemic, in order to establish whether a high rate of transmission results in low strain diversity. Design. Sputum specimens collected for 18 months; IS6110-based DNA fingerprint ing. Setting. The communities of Ravensmead and Uitsig, Cape Town, Sou th Africa. Participants. Three hundred and thirty-four pulmonary tuber culosis patients attending the Local Authority Health Care Clinic. Mai n outcome measure. DNA fingerprinting. Results. A total of 334 M. tube rculosis isolates were characterised by IS6110-based DNA fingerprintin g; 209 strains were identified, 199 having 5 or more insertions. Forty of these strains were present in 2 or more patients (clustering - 126 patients in total), which indicates a recent transmission rate of 30% . The 163 unique strains suggest reactivation of latent infections. Co mputer analysis showed a high degree of strain diversity, and a common progenitor could only be linked to 33% of the strains. Clustering was shown in 50% of drug-resistant isolates. Conclusions. The low rate of transmission (30%) and the high degree of strain diversity (209 strai ns) was unexpected and unexplained, given the high burden of disease i n this community. The clustering of drug-resistant strains suggests th at transmission, rather than lack of compliance, drives the spread of antibiotic resistance in this community. Preliminary indications are t hat BCG vaccination, while having little effect on the incidence of tu berculosis in this community, may have altered the strain dynamics.