Introduction to GeneXpert MTB/RIF Ultra

In December 2010, the World Health Organisation (WHO) endorsed the GeneXpert instrument using the Xpert MTB/RIF cartridge for the diagnosis of Tuberculosis (TB). A more sensitive cartridge, GeneXpert MTB/RIF Ultra, is now available. The Ultra test increases the detection of TB cases, particularly amongst patients living with HIV, using the same specimen types, specimen volumes, current GeneXpert instrumentation platforms, and the same specimen processing protocols.

Recently a multi-centre (10 site, 8 country) study determined the non-inferiority of the Ultra test compared to the current GeneXpert MTB/RIF in diagnosing pulmonary TB among adults. The multicentre study was performed in collaboration with CDRC, FIND, National Priority Programmes (NPP) of the National Health Laboratory Service/University of the Witwatersrand, and University of Cape Town. The primary study observed a 6% increase in sensitivity (for the detection of TB) of the Ultra version over GeneXpert, with an increase of 17% among smear-negative culture positive participants, and 14% among HIV co-infected participants. Similar findings of increased sensitivity among smear negative and HIV co-infected individuals was found in South African participants.

The Ultra test is more sensitive than GeneXpert as it identifies different multi-copy amplification targets as well as improvements in assay chemistry and cartridge design. Ultra also reports semi-quantitative categories as GeneXpert (very low, low, medium and high), but additionally includes a new category termed ‘trace’. The criteria for interpreting ‘MTB detected trace’ result is covered during training and automated comments will be included on TRAK in alignment with the diagnostic algorithm. The Xpert MTB/RIF Ultra assay runs on the newly upgraded GeneXpert software version 4.7b (applies to GX4 & GX16 system platforms) and the Infinity platform software version 6.5a.

Implementation of the Xpert MTB/RIF Ultra assay national rollout will follow a phased approach moving from province to province, commencing in Gauteng. The training of laboratory staff will align with the Xpert MTB/RIF Ultra rollout plan, be conducted prior to site reagent changeover and updated documentation and assay files distributed ahead of Ultra kit shipments. Communication of schedules will allow for workflow planning prior to initiating each phase rollout.

Further communication on the GeneXpert MTB/RIF Ultra national rollout to follow. Should you have any queries in the interim, please contact the NPP on 011 489 8836.

Kind Regards,
Puleng Marokane
GeneXpert Programme Manager
National Priority Programmes
011 489 8839