Consequences of rpoB mutations missed by the GenoType MTBDR plus assay in a programmatic setting in South Africa.

Missed rifampicin resistance was mostly due to the I491F mutation located outside the MTBDR detection area and the L452P mutation, which was not included in the initial version 2 of the MTBDR. This led to substantial delays in the initiation of appropriate therapy. The previous tuberculosis treatment history and the high level of resistance to other anti-tuberculosis drugs suggest an accumulation of resistance.