Describe the laboratory approach to congenital infection and neonatal sepsis.

Congenital Infection

• The classical group is torch — TOxoplasma, Others (syphilis, varicella, parvovirus B19, HIV, hepatitis B, Zika), Rubella, Cytomegalovirus and Herpes simplex
• The "torch screen" as usually ordered is a poor test — a panel of IgG results in an infant reflects maternal antibody, is positive in most of an Indian population, and answers no question. It should be replaced by targeted testing directed by the clinical findings
• The general principles are two: IgM does not cross the placenta, so IgM in the infant must be its own and indicates congenital infection; and maternal IgG crosses and persists for up to 18 months, so infant IgG is uninterpretable unless followed serially or compared with the maternal titre

• The calcification pattern separates the two commonest congenital infections.
• diffuse scattered intracranial calcification points to toxoplasmosis
• periventricular calcification points to cytomegalovirus. Both may present with a small head and a deaf infant, and the imaging distinction is available immediately while serology takes days — and it directs which targeted test to send rather than ordering a panel that answers nothing.

Neonatal Sepsis

• Early-onset sepsis (within 72 hours) is acquired from the maternal genital tract before or during delivery. Risk factors are prolonged rupture of membranes beyond 18 hours, maternal fever, chorioamnionitis, prematurity and unclean delivery. Organisms are group B streptococcus and E. Coli in Western series, but in India Klebsiella, E. Coli, Acinetobacter and S. Aureus predominate
• Late-onset sepsis (after 72 hours) is acquired from the environment, from hands and from devices — coagulase-negative staphylococci, S. Aureus, Klebsiella, Acinetobacter, Pseudomonas and Candida
• The clinical presentation is non-specific — poor feeding, lethargy, temperature instability (often HYPOthermia rather than fever), respiratory distress, apnoea, abdominal distension, jaundice and seizures. "Not doing well" is the presentation, and a low threshold for investigation and treatment is correct because deterioration is rapid
• Investigations — blood culture (1 to 3 mL, which is a large volume for a neonate but essential); a sepsis screen comprising total and differential leucocyte count, immature-to-total neutrophil (I:T) ratio above 0.2, C-reactive protein and micro-ESR, of which two or more positive components support the diagnosis; lumbar puncture, since meningitis accompanies a significant proportion and cannot be predicted clinically; urine culture in late-onset sepsis; and a chest radiograph
• Treatment is started immediately on suspicion, guided by the local antibiogram, and reviewed at 48 to 72 hours with de-escalation or discontinuation

Applied Aspects

• Do not order a "torch screen"; order the specific test suggested by the findings, and interpret it knowing what maternal antibody does
• Test urine or saliva within 3 weeks for congenital cytomegalovirus, or the opportunity to prove it is lost permanently — and with it the case for valganciclovir, which improves hearing outcomes
• Compare the infant's VDRL titre with the mother's; a fourfold higher titre indicates the infant's own infection rather than transplacental antibody
• Diagnose infant HIV by DNA PCR, never by antibody before 18 months
• Take an adequate blood culture volume even in a small neonate; the temptation to take 0.5 mL produces a falsely negative culture and commits the baby to empirical treatment
• Prevention matters more than diagnosis in India — clean delivery practices, antenatal screening for syphilis and HIV, hepatitis B birth-dose vaccination, exclusive breastfeeding, hand hygiene in the newborn unit and kangaroo mother care, which reduces neonatal infection and mortality measurably at no cost
• Hypothermia rather than fever is the commoner temperature abnormality in neonatal sepsis, and a cold baby who is feeding poorly deserves the same urgency as a febrile one