Impetigo and bacterial skin infection — branching viva

Opening question

Examiner: Take me through this child. What is the diagnosis, and what is your frame for managing it? [1]

Candidate: The most likely diagnosis is non-bullous impetigo — the honey-coloured, weeping crust spreading from the nose across the cheek and onto the sibling, in an otherwise well, afebrile child, is the classic presentation of the commonest bacterial skin infection of childhood. My frame is three-layered: treat the individual lesion with the least antibiotic that will work, control the household and school spread, and watch for the post-streptococcal complications. Because the child is well with localised lesions, this is a community-managed case with a short topical course and clear advice on exclusion and hygiene. [1] [2]

Examiner: How do you classify impetigo, and which form is dangerous? [1]

Candidate: Two forms. Non-bullous impetigo is about seventy percent — the honey-coloured crust, caused by Staphylococcus aureus or group A streptococcus. Bullous impetigo is about thirty percent — flaccid bullae caused exclusively by exfoliative-toxin-producing S. aureus. The dangerous end of the same spectrum is staphylococcal scalded skin syndrome, where the toxin circulates systemically in a neonate or young infant and causes widespread tender erythema and sheet-like desquamation. This child has the benign form; I would still examine for any sign of deeper extension or toxin-mediated appearance. [1] [8]