Window period of acute infection

The window period represents the period between the time of initial infection with HIV and the time when HIV antibodies can be detected in the blood stream. During this period, HIV replicates in the blood and lymph nodes; patients are highly infectious and may be symptomatic, but their blood will test negative for HIV antibody. The window period can last up to 12 weeks and may vary between assays using different methodologies.

HIV infection cannot be successfully diagnosed during the window period using antibody-based assays. Assays which detect part of the virion (as opposed to the antibody of the infected host) are employed in this situation.

The tests most commonly used in this situation are the p24 antigen and the proviral HIV DNA assays.

The p24 antigen assay detects the viral protein p24. The assay has high specificity (>95%) but its sensitivity is low (80%).

The proviral DNA detects the presence of HIV DNA that is integrated into the host genes in peripheral blood lymphocytes.

This assay is based on polymerase chain reaction (PCR) technology and is highly specific as well as highly sensitive (98% and >99%, respectively).

The performance of this test in detection of HIV-1 and non-HIV-1 subtypes has not been determined. The HIV DNA assay is available only in the research setting.

HIV RNA PCR tests are not recommended for the diagnosis of acute HIV infection because of the significant rates of false-positive results (10%). Typically, true positive results are greater than 100,000 copies/ml whereas false-positive results are generally less than 1000 copies/ml.

20-05-2015