With the p24 antigen combined in assays, HIV infections can be detected from few days to many weeks before antibody seroconversion, and this is useful in routine screening of blood. Recently, new fourth generation screening assays which permit a simultaneous detection of HIV antigen and antibody have been developed and have reduced the diagnostic window phase between time of HIV infection and laboratory diagnosis on average by four days in comparison to third-generation antibody assays because antibodies to HIV are absent in the very early phase of HIV infection. However, testing strategy using WB is very costly for use in resource-limited countries like Tanzania. In developed countries, screening of HIV antibodies was followed by confirmatory testing, most commonly by using Western blot (WB) assay. Currently, a combination of antibody ELISA, or simple rapid assays based on different test principles have been used in alternative diagnostic testing strategies for laboratory diagnosis in resource-limited countries. The UNAIDS/WHO has given recommendations for the use of combined screening assays for the diagnosis and confirmation of HIV infection. The standard procedure for laboratory diagnosis of HIV infection usually includes screening for virus-specific antibodies using an enzyme-linked immunosorbent assay (ELISA), followed by confirmatory testing of screening positive sample. The enzyme-linked immunosorbent assays (ELISAs) are the most commonly used techniques for the laboratory diagnosis of HIV infection. One of the key issues to achieve this goal is to shorten the so-called “diagnostic window period” when the humoral immune response toward the virus is not fully developed during the acute phase of HIV-1 infection. Early diagnosis of this infection is critical in providing effective antiviral treatment and to prevent transmission. Human immunodeficiency virus (HIV) infection remains an important public health concern in most of the developing countries including Tanzania.
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