Performance of the Abbott RealTime MTB and MTB RIF/INH assays in a high TB and HIV coinfection setting in South Africa.

ABSTRACT

Background: South Africa is a country with a high incidence of tuberculosis (TB), complicated by coinfection with HIV. The Xpert MTB/RIF (Cepheid, Sunnyvale, CA, USA) is used in South Africa as the test for initial diagnosis of TB, and other molecular platforms such as the m2000 (Abbott Molecular, Des Plaines, IL, USA) are widely used for molecular monitoring of HIV viral load. This latter platform is now also equipped with the RealTime MTB and RealTime MTB RIF/INH assays for TB and first line drug resistance screening, but has not been evaluated in settings of HIV and TB coinfection.

Methods: A prospective clinical validation study was conducted at a community health centre in Johannesburg, South Africa, and enrolled consenting, presumptive pulmonary TB individuals. Performance of the Abbott assays was compared to Xpert MTB/RIF, liquid culture, drug susceptibility testing and clinical case definition.

Results: Statistical analysis was performed on 206 individuals (73% HIV positive). Sensitivity and specificity of RT MTB was 82.5%(CI:67.2,92.7) and 93.1%(CI:86.2,97.2) on raw sputum and 77.5%(CI:61.5,89.2) and 95.1%(CI:88.9,98.4) on concentrated sputum respectively, compared to liquid culture. RT MTB correctly identified 17/35 more smear-negative, culture-positive specimens than Xpert MTB/RIF. Both RT MTB and Xpert MTB/RIF displayed sensitivities >70% and specificities >90% in HIV-positive individuals. Available drug-resistance results concurred with MTBDRplus and drug susceptibility profiles.

Conclusion: The RT MTB assay has similar diagnostic performance to Xpert MTB/RIF and is suited to testing presumptive TB patients coinfected with HIV. Existing laboratory information system connectivity, training and technical support makes this a viable polyvalent option to scale up TB alongside HIV laboratory testing services in South Africa.