Transmission of Mycobacterium tuberculosis in a family proved by genotyping

Background/Purpose: Molecular genetic methods have been applied in various epidemiologic studies including investigations of disease acquisition by contact. This report describes the use of various molecular genetic methods in tracing possible household transmission of tuberculosis by contact. Methods: Four Mycobacterium tuberculosis strains, each from four members of a family, were first isolated and identified in the clinical laboratory of the Chest Hospital and were submitted to the National Reference Laboratory of Mycobacteriology for further confirmation and genotyping. In this study, IS6110 restriction fragment length polymorphism (RFLP), spacer oligonucleotide typing (spoligotyping) and mycobacterial interspersed repetitive units-variable number tandem repeats (MIRU-VNTR), and rpoB gene sequencing were used for genotyping. Results: All four strains were found to have identical spoligotypes, MIRU-VNTR patterns, and similar IS6110 RFLP profiles. The results of the drug susceptibility test and of rpoB sequencing showed that all four strains were rifampicin resistant. Conclusion: Household transmission through close contact was thus proved by genotyping. We conclude that all four family members were infected with the same lineage of M. tuberculosis.