Early infant HIV diagnosis — DTM&H MCQ
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Correct answer: A — HIV DNA PCR (virological test)
The correct answer is A, HIV DNA PCR (virological test). In a child under 18 months of age, maternal IgG antibodies acquired transplacentally can persist and cross react on antibody based assays, making serology unreliable for diagnosing true infection in this age group. This child is also still breastfed, so ongoing exposure means infection could be very recent, and the diagnosis requires a test that detects the virus itself (proviral DNA) rather than a host antibody response. WHO early infant diagnosis guidance, which underpins practice in high prevalence, resource limited settings relevant to tropical medicine practice, recommends virological (PCR) testing at first contact, 6 weeks, and again at least 6 weeks after complete cessation of breastfeeding, with confirmation on a second specimen if positive. Why the other options are wrong: C. HIV antibody rapid test: Detects maternal IgG that can persist well beyond 12 to 18 months, and continued breastfeeding means fresh antibody transfer is also possible, so a positive result cannot distinguish maternal antibody from true infant infection. D. p24 antigen test: Has poor sensitivity in infants, especially once antibody complexes form, and is not validated or recommended as a diagnostic tool for paediatric HIV infection. B. Western blot: This is a confirmatory antibody assay used in adults and older children with a mature immune response; it suffers the same maternal antibody interference problem as the rapid antibody test and has no role in infants under 18 months. E. CD4 count: Reflects immune status and staging, not diagnosis; a normal CD4 count does not exclude infection and an abnormal one is not specific for HIV. Key point: Under 18 months, and especially while breastfeeding continues, diagnosis of HIV in an exposed infant requires a virological (DNA/RNA) test, not an antibody based assay, because passively acquired maternal antibody invalidates serology.
Reference: World Health Organization, Consolidated Guidelines on HIV Testing Services, and WHO Early Infant Diagnosis recommendations: virological (HIV DNA PCR) testing for infants under 18 months, including retesting 6 weeks after complete cessation of breastfeeding. https://www.who.int/publications/i/item/9789240031593