Background: Viral kinetics impact humoral immune response to HIV; antibody avidity
testing helps distinguish recent (<6 months) and long-term HIV infection. This study aims to determine
the frequency of recent HIV-1 infection among clients attending ICTC (Integrated Counselling
and Testing Centre) using a commercial EIA, to correlate it with a modified in-house avidity assay
and to study the impact of ART on anti-HIV-1 antibody maturation.
Methods: Commercial LAg Avidity EIA was used to detect antibody avidity among 117 treatment
naïve HIV-1 infected individuals. A second-generation HIV ELISA was modified for in-house antibody
avidity testing and cutoff was set based on Receiver Operating Characteristic (ROC) analysis.
Archived paired samples from 25 HIV-1 infected individuals before ART and after successful ART;
samples from 7 individuals responding to ART and during virological failure were also tested by
LAg Avidity EIA.
Results: Six individuals (5.1%) were identified as recently infected by a combination of LAg avidity
assay and HIV-1 viral load testing. The modified in-house avidity assay demonstrated sensitivity
and specificity of 100% and 98.2%, respectively, at AI=0.69 by ROC analysis. Median ODn values
of individuals when responding to ART were significantly lower than pre-ART [4.136 (IQR 3.437–
4.827) vs 4.455 (IQR 3.748–5.120), p=0.006] whereas ODn values were higher during virological
failure [4.260 (IQR 3.665 – 4.515) vs 2.868 (IQR 2.247 – 3.921), p=0.16].
Conclusion: This modified in-house antibody avidity assay is an inexpensive method to detect recent
HIV-1 infection. ART demonstrated significant effect on HIV-1 antibody avidity owing to
changes in viral kinetics.