RESULOTION OF GEENIUS HIV-1/2 NEGATIVE OR INDETERMINATE RESULTS WITH XPERT QUAL ASSAY

Background: Diagnosis of HIV infection is a multistage algorithm. Following screening with 4^th generation combination immunoassay, confirmation of HIV infection is performed with an antibody assay that differentiates HIV-1 from HIV-2 infection. In the newly updated algorithm, samples that are nonreactive or indeterminate in the differentiation assay are to be tested with an HIV-1 nucleic acid amplification (NAAT) test for resolution. Xpert HIV-1 Qual is a new NAAT assay approved for the identification of HIV infection in whole and dried blood.

Objectives: To assess the performance of Xpert HIV-1 Qual supplementary assay in resolving the clinical status of serum samples reactive by 4^th generation immunoassays and indeterminate or negative by Geenius HIV-1/2 confirmatory assay.

Study design: Samples from 532 individuals which were reactive on Architect and Vidas 4^th generation HIV-1/2 combination immunoassays and either negative or indeterminate by HIV-1 Geenius assay (n=97) were tested with Xpert Qual HIV-1 assay.

Results: Xpert Qual assay correctly classified all 97 samples from HIV-1 positive (n=49) and negative (n=48) individuals. The overall sensitivity and specificity of Geenius confirmatory assay together with Xpert Qual as a supplementary assay when using the true HIV status as a reference were 100% (99.1-100% at 95% confidence interval [CI] and 92.6%-100% at 95% CI, respectively).

Conclusions: Applying Xpert Qual HIV-1 assay in the new HIV multi-stage diagnostic algorithm correctly classified 100% of 532 HIV-1 infections including 49 from HIV-1 carriers who have not yet seroconverted. With this assay the turn-around time required for HIV diagnosis could be significantly reduced.