Congenital and perinatally acquired infections: Viva

Branch 1: Pattern recognition and differential diagnosis

The candidate should recognise the combination of microcephaly, petechiae, and hepatosplenomegaly as the classic multi-system congenital infection syndrome and immediately generate a differential organised around the TORCH framework: CMV, toxoplasmosis, rubella, syphilis, parvovirus, varicella, and - in the right epidemiological context - Zika. The examiner should probe for pattern-recognition clues: periventricular calcifications point to CMV, diffuse intracranial calcifications with chorioretinitis to toxoplasmosis, cataracts with cardiac disease to rubella, snuffles and a palmoplantar rash to syphilis, and severe microcephaly with subcortical calcifications to Zika. [2]

The candidate should also generate the non-infectious differential: inborn errors of metabolism, chromosomal anomalies and syndromic microcephalies, rhesus or ABO haemolytic disease, neonatal alloimmune thrombocytopenia, and congenital leukaemia. The mark of a strong candidate is framing the congenital infection diagnosis as one of pattern recognition and exclusion, supported by targeted microbiology rather than a blanket TORCH panel. [2]

Branch 2: Diagnostic strategy and timing

The candidate must demonstrate a targeted diagnostic approach driven by the clinical question. For suspected congenital CMV, the gold standard is urine or saliva PCR within the first three weeks of life - the candidate should articulate why this window matters, namely that after three weeks a positive result cannot distinguish congenital from postnatal acquisition. They should mention retrospective testing of the neonatal blood spot when the window has passed. [1]

For serology, the candidate should explain IgG avidity (low avidity indicates primary infection within the preceding three to four months, most useful in the first trimester) and the meaning of IgM (it does not cross the placenta, so fetal or neonatal IgM indicates a de novo immune response, though sensitivity varies). They should know that for toxoplasmosis, PCR of amniotic fluid is the prenatal test of choice after 18 weeks, and that for syphilis a non-treponemal test quantifies disease activity while a treponemal test confirms infection, interpreted against maternal titres. [2]

Branch 3: Organism-specific therapy and prevention

The candidate should give organism-specific therapy. For symptomatic congenital CMV with central nervous system involvement, six months of oral valganciclovir 16 mg per kg twice daily improves hearing and neurodevelopmental outcomes (Kimberlin et al trial), with neutropenia the main adverse effect requiring blood-count monitoring. For toxoplasmosis, pyrimethamine plus sulfadiazine plus folinic acid is given for approximately a year; spiramycin is used only to prevent transmission before fetal infection is confirmed. Congenital syphilis is treated with 10 days of aqueous penicillin G, and the candidate should stress that the condition is entirely preventable with maternal benzathine penicillin at least 30 days before delivery. [1]

The examiner should then pivot to prevention. For parvovirus B19 hydrops, intrauterine transfusion is life-saving - approximately 85 per cent survival with transfusion versus nil without in severe hydrops. For hepatitis B, HBIG plus the first vaccine dose within 12 hours of birth prevents transmission. For perinatal HIV, maternal combination antiretroviral therapy is the cornerstone; where the mother had no antenatal care, a two-drug infant regimen is superior to zidovudine alone. Finally, the candidate should articulate the lifelong surveillance plan: audiology, developmental follow-up, neuroimaging, and ophthalmology, because the late emergence of hearing loss and developmental delay is the rule rather than the exception. [3]