Impetigo in Children
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Direct answer
Impetigo is a superficial bacterial skin infection that presents either as the common non-bullous form — periorificial, perilesional honey-coloured crusts on an erythematous base — or as flaccid, rapidly spreading bullae caused by staphylococcal exfoliative toxin. Limited disease is treated with topical mupirocin 2 per cent three times daily for five days; extensive or bullous disease needs systemic anti-staphylococcal therapy. The paediatric point that examiners probe is the aftermath: streptococcal impetigo can trigger post-streptococcal glomerulonephritis two to four weeks later, even from skin that looked trivial, whereas skin strains do not cause rheumatic fever.
What you must remember
- Non-bullous impetigo (about 70 per cent of cases): Staphylococcus aureus with or without group A streptococcus; starts as a vesicle or pustule that ruptures and dries into the classic golden, stuck-on crust.
- Bullous impetigo: S. aureus producing exfoliative toxin A; flaccid, thin-roofed bullae with clear yellow fluid, minimal surrounding erythema, usually in neonates and young infants.
- Preferred topical agent: mupirocin 2 per cent ointment three times a day for five days to localized lesions; fusidic acid is an alternative.
- Extensive, bullous or systemic disease: oral cephalexin, cloxacillin or amoxicillin-clavulanate; cover community-acquired MRSA if it fails.
- Gently remove crusts with soap and water; keep nails short; the child may return to school 24 hours after starting effective treatment.
- Watch for post-streptococcal glomerulonephritis at two to four weeks — new periorbital puffiness, cola-coloured urine, hypertension — even after the skin has healed.
- Streptococcal pyoderma is nephritogenic but not rheumatogenic: pharyngeal strains trigger both, skin strains only nephritis. This asymmetry is a favourite viva question.
- Differential diagnosis that matters: herpes simplex is painful with clustered vesicles on an erythematous base; scabies spares the face and burrows at the wrists; molluscum are umbilicated pearly papules.
- Recurrent impetigo in one family means a staphylococcal carrier — treat carriage in the nose and consider underlying skin disease such as eczema.
A typical exam case
An eighteen-month-old is brought for yellow crusts around the nose and mouth that started as "small boils" five days ago, with a sibling having similar lesions. The child is afebrile and feeding well. This is non-bullous impetigo: well-looking child, periorificial crusted lesions, a household focus. Treatment is hygiene plus mupirocin 2 per cent three times daily for five days, and examination of the sibling so the ping-pong infection stops. Ask about eczema — broken atopic skin is the platform on which impetigo recurs — and about recent scabies, which children scratch into secondarily infected.
Contrast the two-month-old with a large flaccid bulla on the groin that peels with gentle wiping. In an ill or febrile infant, the fear is staphylococcal scalded skin syndrome, where disseminated toxin causes widespread tender erythema with positive Nikolsky sign and the child needs admission, fluid care and systemic anti-staphylococcal cover; in bullous impetigo the child is typically well and the disease stays localised. The exam question is designed to see whether you escalate appropriately in the neonate and reassure appropriately in the toddler.
Two weeks later the first child returns with puffy eyes and smoky urine. Urinalysis shows red cell casts, complement C3 is low, and ASLO may be normal because skin strains are ASLO-negative — anti-DNase B titre rises instead. Management of post-streptococcal glomerulonephritis is supportive: salt restriction, diuretics for oedema, antihypertensives if needed, with an excellent prognosis in children.
How the exam frames it
Expect matching-type and one-best-answer questions built on appearance and consequence rather than on bacteriology alone. A photograph of honey-coloured crusts asks for mupirocin; a description of "peeling around the mouth after a sore throat" asks you to distinguish perioral streptococcal disease; and the stem "child treated for impetigo two weeks ago now has hypertension and haematuria" is testing whether you connect skin to kidney and know that C3 falls and recovers. Candidates also lose marks by claiming that skin streptococci cause rheumatic fever, which they do not.
Frequently asked questions
What distinguishes bullous from non-bullous impetigo?
Bullous impetigo is caused by S. aureus exfoliative toxin A and shows flaccid, thin-walled bullae with little erythema; non-bullous disease presents as ruptured pustules drying into golden crusts and may be staphylococcal, streptococcal or mixed.
Which complication follows streptococcal impetigo but not streptococcal pharyngitis's rheumatic sequelae?
Post-streptococcal glomerulonephritis can follow either skin or throat infection, but rheumatic fever follows pharyngitis alone — pyoderma strains are nephritogenic, not rheumatogenically associated.
What is the first-line treatment for localised impetigo?
Topical mupirocin 2 per cent three times daily for five days after crust removal with soap and water; systemic antibiotics are reserved for extensive, bullous or recurrent disease.
Why can ASLO titre be normal in post-streptococcal glomerulonephritis after impetigo?
Skin streptococci are poorly immunogenic for streptolysin O; anti-DNase B and antihyaluronidase titres rise instead, so ASLO is an insensitive marker of pyoderma-associated nephritis.
When should a neonate with bullous lesions be admitted?
When lesions are extensive, the infant is febrile or irritable, or Nikolsky sign is positive — staphylococcal scalded skin syndrome needs systemic antibiotics, fluids and inpatient monitoring.