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Background:  It is difficult to identify recently-infected HIV-1 patients for large field studies and in settings where collection, centrifugation, storage, and shipment are difficult. The current study validated an immunoassay able to identify recent HIV-1 infections that can be used on dried blood spots (enzyme immunoassay (EIA)-RI, for ELISA for recent infection).

Methods:  A single indirect ELISA format was developed to quantify antibodies present in sera from HIV-1-infected individuals toward 2 HIV-1 antigens:  consensus peptides of the immunodominant epitope of gp41 (IDE) and consensus V3 peptides (subtypes A, B, C, D, CRF01_AE).  Only serum samples from patients with known date of infection were used for the present purpose.  Filter paper was spotted with 20 µl of serum and allowed to dry.  The eluted serum was then subjected to the EIA-RI.  The serum samples were divided into a training sample (n = 260) and a validation sample (n = 500) to allow an external validation of the parameters estimated in the training sample. The aim of the statistical analysis was to classify the samples in 2 groups:  those corresponding to a recent infection (≤ 6 months) and those not corresponding to a recent infection.  A logistic regression was used for this purpose, with 2 techniques, a bootstrap re-sampling procedure and generalized estimating equation (GEE) logistic models. Thresholds were explored using ROC curves. The final threshold was chosen on the basis of the sensitivity and specificity levels obtained on the validation sample to get the best sensitivity given an overall specificity higher than 95%.

Results:  Combining quantification of antibody binding to the IDE and V3 peptides allowed us to identify recent infections (≤ 6 months) with sensitivity of 87.0%, with a specificity of 98.0% in patients with long-term infection (but not AIDS) and 90.9% in patients suffering from AIDS in the validation sample.

Conclusion:  This simple immunoassay allows the identification of recently HIV-1-infected patients with performances compatible with its use in the determination of the HIV-1 incidence in population-based studies. Its application to dried blood spots is particularly relevant for large field studies and in settings where collection, centrifugation, storage, and shipment are difficult.

Keywords: Incidence; Immunoassay; Epidemiology