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Serum sickness — RACP Paediatrics MCQ

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ModerateIDSerum sicknessRACP Paediatrics

A 12-year-old develops urticaria, arthralgia, fever, and lymphadenopathy 10 days after receiving IV cefazolin for a surgical wound infection. Serum complement (C3, C4) is low. What is the most likely diagnosis?

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Correct answer: E — Serum sickness

Urticaria, arthralgia, fever, and lymphadenopathy 7-14 days after drug exposure (commonly antibiotics, particularly cephalosporins, or blood products) with low complement is serum sickness (type III hypersensitivity/immune complex-mediated reaction). Management includes stopping the offending drug, antihistamines, and corticosteroids for severe cases. It is self-limiting after drug clearance.

Reference: Australian Therapeutic Guidelines – 2024; RACP Paediatric Curriculum – Allergy/ID