Second worldwide proficiency study on variable number of tandem repeats typing of Mycobacterium tuberculosis complex

The quality of variable number of tandem repeats (VNTR) typing of Mycobacterium tuberculosis was first investigated in 2009 in 37 laboratories worldwide. The results revealed an inter- and intra-laboratory reproducibility of respectively 60% and 72%. These data spurred an improvement in laboratory-specific assays and global standardisation of VNTR typing.

To measure the effects of the technical improvements and increased standardisation, a test panel consisting of 30 M. tuberculosis complex DNA samples was distributed for VNTR typing in 41 participating laboratories from 36 countries.

The inter- and intra-laboratory reproducibility increased overall to respectively 78% and 88%. The 33 laboratories that participated in both the first and second proficiency studies improved their inter- and intra-laboratory reproducibility from 62% and 72% to respectively 79% and 88%. The largest improvement in reproducibility was detected in 10 laboratories that use an in-house polymerase chain reaction technique and perform amplicon sizing using gel electrophoresis. Detailed error analysis revealed a reduction in the number of systematic errors, sample exchange events and non-amplifiable loci.

This second worldwide proficiency study indicates a substantial increase in the reproducibility of VNTR typing of M. tuberculosis. This will contribute to a more meaningful interpretation of molecular epidemiological and phylogenetic studies on the M. tuberculosis complex.