In an infant born to a HIV infected mother, at what age of child the ELISA test can reliably diagnose HIV infection

Enzyme-linked immunosorbent assay (ELISA) and Western blotting are used to initially detect HIV-specific antibodies but these tests are not used for diagnosis in patients younger than 18 months of age. This is because of the persistence of the maternal HIV antibody in infants younger than 18 months. Infants younger than 18 months require virologic assays that directly detect HIV in order to diagnose HIV infection.