Background

The Serological Testing Algorithm for Recent HIV Seroconversion is a simple and cost effective method of diagnosing early HIV infection. Patients were tested for HIV-1 antibodies using a Sensitive Enzyme Immunoassay for screening, and confirmed by a Recombinant Immunoblot assay. All positive samples for HIV-1 were then subjected to the Less Sensitive EIA. Since HIV antibody levels rise during the early months after seroconversion, samples positive on the Sensitive EIA but Negative on the Less Sensitive EIA were considered as cases of recent seroconversion.

Methods

1967 men from August 2001 to December 2002 were enrolled from two sites in Mumbai. (871 from the LTMG Hospital and 1096 from STD Clinic in the red light area of the city). All the sera samples were tested for the Sensitive EIA using Biokit ELISA. All Sensitive EIA positive samples were confirmed by Chiron Immunoblot Assay. Less sensitive EIA was performed on all HIV-1 positive confirmed samples retrospectively, using Modified Vironostika HIV-1 Microelisa system. Plasma for the less sensitive EIA was diluted 1: 20,000 times. Calibrators, low and high positive controls obtained from the Centers for Disease Control (Atlanta, Georgia) were also diluted 1:20,000. Less sensitive EIA was performed with modifications to sample dilution, sample incubation time, and also conjugate incubation time.

 All HIV-1 positive samples were initially run singly on the Less Sensitive EIA in screening mode to look for samples with Specimen Median Optical density < 2.00, which represented recent seroconversion. These were reconfirmed in triplicate and SOD < 1.00 were considered recent HIV-1 seroconversions.

For subtype C which is the predominant subtype in the Indian subcontinent, CDC Atlanta suggests a provisional window period of 360 days by using standardized optical density cutoff value of 1.00.

Results

Of the 1967 patients, 292 were positive for HIV-1 giving a prevalence of 14.84%. Of these 19 were negative by Less sensitive EIA giving HIV-1 incidence of 0.96% using the window of 360 days specific for subtype C.

Conclusions

This study shows an HIV prevalence of 14.6% and incidence of 1.138% while the annualized incidence was 1.13%. Thus HIV incidence monitoring by STARHS is important for preventive intervention strategies as well as for the management of HIV infection.