HIV exposure and infection in children — branching viva

Opening question

Examiner: Take me through this infant. What is the most likely diagnosis, and what is your immediate frame? [8]

Candidate: The most likely diagnosis is Pneumocystis jirovecii pneumonia in an HIV-exposed, unprophylaxed infant of an unsuppressed mother. The age — four months — the hypoxia out of proportion to auscultatory findings, and the diffuse bilateral interstitial infiltrates are the classic picture. My frame is two-layered: keep this infant alive now, and then confirm the HIV status and treat the underlying immunodeficiency. I would give oxygen, admit, start empiric high-dose co-trimoxazole with a corticosteroid for moderate–severe disease, and pursue the diagnosis. [8] [1]

Examiner: Why Pneumocystis specifically? [8]

Candidate: Because PCP is the opportunistic pneumonia of infant HIV, classically presenting between three and six months in an infected, unprophylaxed infant. The hypoxia is disproportionate to the chest findings, the X-ray shows diffuse interstitial infiltrates, and the infant of an unsuppressed, disengaged mother is exactly the child who acquires infection and is missed. The onset is subacute over days but can decompensate over hours, so I treat empirically while confirming. [8]

Branch 1 — why antibody testing fails

Examiner: How will you confirm HIV in this infant — can you just send an antibody test? [7]

Candidate: No — an antibody test is uninterpretable at this age. Maternal IgG crosses the placenta and persists in the infant's blood for up to 18 months, so a positive antibody result would tell me about the mother, not the infant. I must detect the virus directly, with HIV DNA or RNA PCR, and confirm a positive result with a second sample on a separate specimen. Antibody becomes reliable only after maternal antibody has cleared, at around 18 months. [7]

Examiner: And if this had been a 2-year-old? [7]

Candidate: Then antibody testing would be reliable, because by 24 months maternal antibody has cleared. In practice I would still use PCR to confirm rapidly, but a negative antibody test in a child over 18 months — who is not breastfeeding from an infected mother — can exclude infection, whereas the same test at four months cannot. [7]

Branch 2 — pathophysiology and rapid infant progression

Examiner: Why does this infant have such severe disease at four months? [4]

Candidate: Because perinatally-infected infants progress far faster than adults. HIV enters CD4-positive T-cells via gp120 and the CD4 receptor, reverse transcriptase integrates proviral DNA into the host genome, and progressive CD4 depletion through lysis, apoptosis and immune-mediated killing dismantles the immune defence. In an infant the immature immune system, the large thymic pool of susceptible naïve T-cells and a high viral set-point drive a rapid CD4 decline — so the same virus that takes a decade in an adult reaches AIDS within months in a baby. A pooled African analysis showed about half of untreated infants dead or with AIDS by age two. [4] [1]

Branch 3 — definitive treatment and the CHER evidence

Examiner: Once the infant is stable and HIV is confirmed, what definitive treatment will you start? [1]

Candidate: Antiretroviral therapy, immediately — the current guidance treats every infected child at any age and stage. I would use a WHO-recommended first-line paediatric regimen — an NRTI backbone plus a third agent, weight-based dosed — and monitor the viral load to confirm suppression. The justification is the CHER trial: starting ART in asymptomatic infants reduced mortality by about 76% and HIV progression by 75%, compared with waiting for clinical or immunological decline. Waiting for this infant to worsen before treating is the error the trial was designed to correct. [1] [5]

Examiner: And cotrimoxazole? [8]

Candidate: Yes — cotrimoxazole prophylaxis for all infected children, regardless of stage, because it prevents Pneumocystis and other bacterial infection and reduces mortality. This infant should never have been without it; starting it now and continuing it is part of the definitive bundle alongside ART, nutrition, growth surveillance and opportunistic-infection care. [8]

Branch 4 — prevention of the next case

Examiner: This infant was missed. How do we prevent the next one? [7]

Candidate: Through the PMTCT cascade. The single strongest predictor of no vertical transmission is a maternal viral load that is undetectable at delivery, so the backbone is maternal lifelong ART — Option B+ — with viral suppression maintained through pregnancy. Around that: universal antenatal HIV screening, infant nevirapine prophylaxis, cotrimoxazole from four to six weeks, safe infant feeding counselled to the setting, and a structured PCR follow-up to a final negative antibody at 18 to 24 months. This mother was disengaged from care — so the prevention failure here is an engagement failure, and the remedy is a cascade that does not let families fall out of it. [7] [4]

Examiner: What about the family? [7]

Candidate: Offer partner and sibling testing, link the mother back into HIV care with adherence support, and address the social determinants — stigma, transport, housing, mental health — that drove the disengagement. A technically correct plan fails if the family is not supported, so the public-health layer extends deliberately into the social context. [7]

Branch 5 — the adolescent and the long view

Examiner: If this infant survives and is treated, what does the future look like? [5]

Candidate: With sustained viral suppression and engagement in care, the prognosis is transformed — children who suppress virus and stay connected survive into adulthood with near-normal life expectancy. The long-term work is lifelong ART with viral-load monitoring and adherence support, nutrition and growth surveillance, immunisation, and a planned transition to adult care in adolescence. The transition is planned early — years before — because the disengaging adolescent is the patient most at risk of returning to AIDS. The prognosis depends as much on staying in care as on the biology. [5] [1]

Wrap

Examiner: Summarise the paediatric HIV stance in one sentence. [7]

Candidate: Separate exposure from infection by PCR not antibody, recognise and treat Pneumocystis empirically in the hypoxic infant, start ART immediately in every infected child, give cotrimoxazole to all, and prevent the next case through maternal viral suppression, infant prophylaxis and a cascade that holds every family — because the virus is lifelong but the outcomes are decided by the cascade. [1] [7]