Genotyping of M. tuberculosis isolates has been used to support investigations of local outbreaks. Molecular methods have revolutionised our understanding of the transmission of tuberculosis showing that clustered cases indicate recent transmission while distinctive genotypes represent a reactivation of the past infection. The aim of our study was to investigate a connection between M. tuberculosis strains isolated from potentially linked cases. A total of 12 isolates originating from three local outbreaks, one hospital and two communities (a family and a shared household) were included in the study. Isolates were analysed by a high-resolution typing method, MIRU-VNTR analysis (Mycobacterial Interspersed Repetitive Units - Variable Number Tandem Repeats). Twelve MIRU loci vary in tandem repeat numbers and, in most, sequence between repeat units. PCR-based genotyping of these12 MIRU loci yields different patterns that can be used for the comparison of M. tuberculosis strains. In the hospital outbreak there were more than one genotype present, indicating that there was no common source of infection. Transmission was confirmed only for the cases of the shared household but not the family. In conclusion, our results suggest that genotyping by means of MIRU-VNTR analysis can be a useful adjunct to standard contact investigations and can be used to identify unsuspected transmission and broaden the scope of contact investigations.

Temeljne medicinske znanosti,Kliničke medicinske znanosti