Short Communication: Low False Recent Rate of Limiting-Antigen Avidity Assay Among Long-Term Infected Subjects from...

Assays used for HIV cross-sectional incidence testing can misclassify some individuals with nonrecent HIV infection as recently infected, overestimating HIV incidence. We analyzed the frequency and factors associated with false-recent misclassification on subjects from Quangxi, China known to have long-term infection using the limited antigen-avidity assay (LAg-Avidity). Stored samples from treatment-naive individuals from Guangxi, China were tested using the LAg-Avidity. A total of 362 samples from individuals known to be infected 2 to 13.5 years were tested and the false-recent rate (FRR), the frequency of samples with a positive result, was determined at different cutoff values of the assay. Additionally, factors associated with misclassification were determined. The FRR of the LAg-Avidity was 1.1% (4/362) using a cutoff of 1.5 normalized optical density units (OD-n). All four samples had viral loads >1,000 copies/ml. Using a cutoff of 3.0 OD-n the FRR was 5.5% (20/362), with four samples having viral loads <1,000 copies/ml. Factors associated with a higher odds of misclassification were female gender (OR 7.7, 95% CI 1.0-56.4) and being a female sex worker (OR 31.3, 95% CI 4.0-242). At the higher cutoff, being of Zhuang decent, relative to Han, had higher odds of misclassification (OR 6.2, 95% CI 1.99-19.0). The LAg-Avidity assay had a low FRR in this Chinese population. Further investigations of the higher frequency of low LAg-Avidity results seen in female sex workers and individuals of Zhuang descent should be explored in a larger study.