This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
All of the following methods are used for the diagnosis of HIV infection in a 2 month old child, 
Select and explain. 
A. DNA-PCR., B. Viral culture., C. HIV ELISA, D. p24 antigen assay
C: HIV ELISA
Answer: C: HIV ELISA 
Explanation: Anti-HIV antibody detection by ELISA or any other method is done only after 18 months of birth when all maternal antibodies would have disappeared.
HIV diagnosis <18 months: (i) HIV DNA detection (best), (ii) p-24 antigen, (iii) HIV RNA detection, (iv) virus isolation