Secondary immunodeficiency — branching viva

Oncology ward: a seven-year-old on induction chemotherapy for acute lymphoblastic leukaemia presents with fever and an absolute neutrophil count of 0.2 × 10⁹ per litre. The examiner asks: what is your framework, what is the immediate threat, how will you manage it now, and what prophylaxis belongs in his long-term plan — then branches to a child on long-term high-dose steroids presenting with dry cough and hypoxia and asks you to predict the organism and the defence, and finally to a rituximab-treated child with low IgG and asks you to justify why you would NOT automatically start immunoglobulin.