Paediatric Rashes

❍ At a glance

• The most important initial question is not "what is this rash?" but "does this child look sick?" Non-blanching petechiae or purpura in a febrile or unwell child is a medical emergency - presumptive meningococcal septicaemia. Give IM/IV benzylpenicillin immediately if transfer is not immediate.
• In NZ, impetigo is not merely a nuisance. Skin sores from group A streptococcal impetigo are a major pathway to acute rheumatic fever and rheumatic heart disease, with Maori and Pacific children disproportionately affected.¹ Treat promptly and completely.
• Kawasaki disease: fever >5 days plus at least four of: rash, conjunctivitis, oral changes, extremity changes, cervical lymphadenopathy. Easily missed in incomplete presentations. Refer urgently for IVIG and aspirin.²
• Parvovirus B19 (slapped cheek): inform pregnant contacts - risk of hydrops fetalis, particularly in the first and second trimesters. Children are no longer contagious once the rash appears; school exclusion is unnecessary.

❍ Common presentations

• Roseola infantum (HHV-6) - typically ages 6 months to 2 years. Three to five days of high fever (often 39-40°C) that defervesces abruptly, followed by a rose-pink maculopapular rash on the trunk spreading to the face and limbs. The child is usually well during the febrile phase despite the high temperature. The rash is diagnostic in retrospect - non-pruritic, non-scaly, fades within 24-48 hours. No treatment required; febrile convulsions may occur during the febrile phase.
• Hand, foot and mouth disease (Coxsackievirus A16, Enterovirus 71) - small vesicles or ulcers in the mouth and aphthous-like lesions on the palms, soles, and sometimes buttocks. Common in children under 5; spreads readily in daycare settings. Usually mild and self-limiting over 7-10 days. Enterovirus 71 strains can cause neurological complications - refer if encephalitic features (seizures, ataxia, movement disorder, persistent vomiting). Not the same as foot-and-mouth disease in livestock.
• Slapped cheek (parvovirus B19 / erythema infectiosum) - bright red "slapped" appearance of both cheeks, followed by a lacy reticular rash on the trunk and limbs that may wax and wane for weeks. Children are infectious before the rash appears; by the time of the rash, they are no longer contagious and school exclusion is unnecessary. In immunocompromised individuals or those with haemolytic anaemia, parvovirus B19 can cause aplastic crisis - urgent referral. Inform pregnant contacts (risk of hydrops fetalis, particularly in the first and second trimesters).
• Impetigo - superficial bacterial skin infection (Staphylococcus aureus most commonly; Streptococcus pyogenes particularly in NZ). Honey-coloured crusted lesions or bullous impetigo. Topical mupirocin or fusidic acid for localised disease; oral flucloxacillin or cephalexin for extensive, bullous, or treatment-resistant cases. In NZ, skin sores from group A streptococcal impetigo are a major pathway to acute rheumatic fever and rheumatic heart disease, with Maori and Pacific children disproportionately affected.¹ Treat promptly and completely.
• Molluscum contagiosum - flesh-coloured, dome-shaped papules with a central dell, caused by a poxvirus. Common in primary school-aged children; spreads by skin-to-skin contact and shared towels. Individual lesions resolve spontaneously over 6-18 months; widespread or persistent lesions in older children should prompt consideration of immunodeficiency. No treatment is routinely required - reassure parents. If treatment is desired, cantharidin (applied by a clinician) or curettage are options. Avoid in the periocular area without ophthalmology review.
• Tinea capitis - scaly scalp patches with variable hair loss; in severe cases, a boggy kerion (inflammatory mass) with lymphadenopathy. Predominantly in children; transmitted by person-to-person contact and contaminated fomites. Requires oral antifungal therapy (oral terbinafine or griseofulvin - see the tinea page for dosing). Confirm with scalp brushings or hair clippings for mycology where possible. School exclusion is not required; advise against sharing hats, combs, or hair accessories.
• Henoch-Schönlein purpura (IgA vasculitis) - palpable purpura predominantly over the buttocks and lower limbs, often with arthritis, colicky abdominal pain, and nephritis. Usually follows an upper respiratory infection. Renal involvement (haematuria, proteinuria) requires monitoring - check urinalysis at presentation and follow-up. Most cases resolve spontaneously; refer if significant renal involvement, severe abdominal pain (intussusception risk), or prolonged course. Distinguish from meningococcal purpura: HSP is well-distributed, child is usually not as systemically unwell, purpura is palpable.

❍ Red flags - when to act urgently

Non-blanching petechiae or purpura in a febrile or unwell child: presumptive meningococcal septicaemia until proven otherwise. Give IM/IV benzylpenicillin immediately if meningococcal disease is suspected and transfer is not immediate. Kawasaki disease (fever >5 days plus at least four of: rash, conjunctivitis, oral changes, extremity changes, cervical lymphadenopathy) requires urgent paediatric referral for IVIG and aspirin to prevent coronary artery aneurysm - it is easily missed in incomplete presentations.² Stevens-Johnson syndrome or toxic epidermal necrolysis (widespread blistering and mucosal involvement after drug exposure) requires immediate hospital admission.