Applicability Study Of LAg-Avidity EIA Used In HIV-1Incidence Estimation In China

BackgroundDifferentiating the recent and long-term HIV-1infection by using the laboratory method in cross-sectional investigation, then calculating the HIV-1incidence by a formula became more and more important. Now, the BED-CEIA used in China had some problems, its accuracy can be affected by antiretroviral therapy, HIV-1subtype, CD4+T cells count et al. and the false recent rate of BED assay is higher. To address those problems of BED assay, a new avidity method, limiting-antigen avidity enzyme immunoassay (LAg-Avidity EIA), was developed in these years, the pilot study showed that less factors can affect this new assay and the false recent rate of this assay was much lower than BED assay, which could result in the HIV-1incidence calculated by this LAg-Avidity assay was much closer to the true value.Objectives1. To evaluate the repeatability and accuracy of LAg-Avidity EIA kits, to find out if it can be applied in China HIV network laboratories;2. To obtain the mean duration of recent HIV-1infection of LAg-Avidity assay used in China for incidence calculation;3. To abtain the false recent rate of LAg-Avidity assay used in China for incidence calculation, to find out if the CD4+T cell count is one of the factors which could affect the accuracy of the assay;4. To find out if the antiretroviral therapy could affect the accuracy of the LAg-Avidity assay. Methods1. Evaluate repeatability of the LAg-Avidity kit by testing the controls and calibrator in it and calculating precision of different runs and wells, examining the correlation of ODn values of BOCA101of four technicians, and the correlation of the average ODn values of BOCA101tested by foure technicians with the expected results of this panel; at the same time, evaluating the accuracy of the kit by interpretating the BOCA101panel.2. By testing531seroconversional specimens from two cohort studies (151seroconvertors), analyzing the data by SPSS17.0to obtain the mean duration of recency of the LAg-Avidity assay.3. By testing513long-term infection (diagnosed time longer than two mean duration of recency of LAg-Avidity assay), antiretroviral therapy naive specimens to analyzing the false recent rate of the LAg-Avidity assay.4. By testing720specimens collected from patients under antiretroviral therapy for different years, to find out the influence of the therapy years and the viral load after therapy to the LAg-Avidity assay.Results1. After calibration, the Coefficient of Variation (CV) of high positive control and low positive control were less than10%; the correlation of4technicians was high, and the correlation of the ODn average values of the4technicians with the ODn valuses presented by US CDC was0.9849; the precision of different wells was not so good, which showed the amounts of antigen coated in the wells maybe heterogeneous in lot production. The BOCA101panel had the same interpretation results with the USA CDC expected.2. The false recent rate of LAg-Avidity assay used in China was0.39%(2/513,95%CI0.00%-0.93%), and CD4+T cell counts could not affect this assay (0/52).3. When the cutoff value of LAg-Avidity assay was1.0. the mean duration of recency of this assay used in China was126days.4. Antiretroviral therapy could affect the accuracy of the LAg-Avidity assay, the false recent rate was10.00%(72/720,95%C17.81%-12.19%), there was no evidence showed that the false recent rate correlated with the therapy time, but low viral load (less than1000copies/ml) after therapy could resulted in high false recent rate.Conclusions1. The repeatability and accuracy of the LAg-Avidity kit were better, and this assay can be used in network HIV laboratories all over the China; but the quality of the kits in batch production still needed to be improved.2. Obtained the mean duration of recency and false recent rate of LAg-Avidity assay used in China, the false recent rate was much lower than BED assay’s false recent rate, which could improve the accuracy of HIV-1incidence calculated by the new assay.3. CD4+T cell counts could not affect the LAg-Avidity assay; the antiretrivoral therapy was an important influence factor of the assay, and the specimens collected from patients under antiretroviral therapy should be excluded from cross-sectional survey.