This CDC developed Limiting-Antigen avidity Enzyme Immunoassay (LAg-avidity-EIA) provides an easy way to measure increasing binding strength (avidity) of HIV antibodies as part of maturation HIV antibodies after seroconversion, providing a method to distinguish early-stage from long-term HIV-1 infection. Surveillance of HIV-1 provides information on prevalence rates of the disease, but determination of new infection rates (HIV-1 incidence) is difficult to deduce. Longitudinal follow up is expensive and can be biased.

Unlike assays which use antigens derived from only one subtype and use two wells, this new approach employs a multi-subtype recombinant protein, rIDR-M, to permit equivalent detection of antibody avidity among different subtypes, and measures binding strength of antibody in one well. This assay will allow the simultaneous testing of more specimens and better overall reproducibility due to its design. Further, the approach is likely to be more robust and provide more accurate results. The assay may be used for individual diagnosis of recent or long-term infection, but may also act as an important tool for worldwide HIV-1 surveillance, assessing new trends of infections, and monitoring success of varied and comparable prevention efforts implemented by major public health agencies.