Quantitative Detection of Plasma Human Immunodeficiency Virus Type 2 Subtype A RNA by the Nuclisens EasyQ Assay (Version 1.1)

Abstract

No commercial viral load assay has yet been approved for use for measurement of human immunodeficiency virus type 2 (HIV-2) RNA levels in plasma. We assessed the performance of the NucliSens EasyQ (version 1.1) assay (EasyQ; bioMérieux, Boxtel, The Netherlands) to quantify HIV-2 viremia. A viral stock was prepared from an HIV-2 (subtype A)-infected patient. Culture supernatant was subjected to viral particle counting by electron microscopy. Serial dilutions of the viral stock were made in HIV-negative plasma and were used to test EasyQ for its sensitivity, linearity, and reproducibility. RNA was quantified by the NucliSens EasyQ (version 1.1) assay. Plasma samples from 75 HIV-2-infected patients were further tested. EasyQ was able to quantify HIV-2 RNA in a reproducible manner. Overall, estimates of the number of HIV-2 RNA copies/ml obtained with EasyQ were lower than those obtained by electron microscopy; however, the differences were always less than 0.7 log (mean, 0.55 +/- 0.19 log(10)). The assay showed good linearity (r(2) = 0.964; P < 0.0001). The agreement between both measures was assessed by use of a Bland-Altman plot; the narrow limits (0.158 to 0.952), defined as the mean difference +/- 2 standard deviations, indicated good agreement. The reproducibility was also good, since the between-run coefficients of variation were 1.49, 3.60, and 12.25% for samples containing 6.30, 4.30, and 2.30 log(10) HIV-2 RNA copies/ml, respectively. HIV-2 RNA was detected in 34 of 75 (45%) plasma specimens (mean, 2.72 log RNA copies/ml; range, 1.74 to 4.11 log RNA copies/ml); the rest of the specimens were considered to have undetectable viremia. A negative correlation was found between the number of HIV-2 RNA copies/ml and CD4 counts. In summary, EasyQ was shown to be reliable for the measurement of plasma HIV-2 subtype A RNA levels and may be a feasible tool for routine clinical monitoring of HIV-2 subtype A-infected patients.