Background: Estimation of HIV incidence rates is important for timing interventions, planning prevention studies, and monitoring the epidemic. This requires accurate estimation of the "recency period" (also known as the "window period") between seroconversion and achievement of specific detectable levels of anti-HIV antibody titers, such as the standardized optical density (SOD) in the early phase of HIV-1 infection.
Methods: To obtain a better understanding of interpatient variation of the recency period, prospective measurements of antiviral antibody titers in the early phase of HIV-1 subtype C infection were quantified by Vironostika-LS. Time of seroconversion was estimated by Fiebig staging.
Results: The profiles of SOD values during the first year of infection commonly showed slow initial increase followed by a more rapid increase, although in some patients, SOD values increased rapidly soon after seroconversion. Using an SOD cutoff of 1.0, the average duration of the recency period in subtype C infection in the local epidemic in Botswana was estimated to be 151 days (95% confidence interval: 130 to 172 days) post seroconversion. The recency period was significantly associated (P = 0.007) with the level of viral replication during the first 2-3 months post seroconversion. Reduction of SOD values after initiation of antiretroviral therapy (ART) was a dominant pattern in antiretroviral drug (ARV)-treated subjects.
Conclusions: Our data suggest that HIV incidence estimation based on sensitive/less sensitive enzyme immunoassay cross-sectional testing could be potentially improved by incorporation of viral load levels at the time of detection of a recent infection.