Speediatrics: What’s causing this infant’s widespread and intensely itchy rash?

Scabies is a contagious skin condition caused by infestation with the mite Sarcoptes scabiei var. hominis, which burrows into the stratum corneum, leading to intense itching and skin lesions.

Clinical features

• Presentation:
  • Gradual onset of intensely pruritic, erythematous papules and vesicles.
  • Lesions may appear excoriated due to scratching.
  • Burrows (thin, greyish-white lines) are pathognomonic but can be hard to identify in young children.
• Symptoms:
  • Intense itch, particularly worse at night.
  • Irritability and disturbed sleep are common.
  • Secondary bacterial infection may present with oozing, crusting, or pustules.
• Affected areas:
  • In infants: scalp, face, neck, palms, and soles may be affected.
  • In older children: wrists, ankles, interdigital spaces and trunk.
  • Distribution often includes sites atypical for adults.

Epidemiology

• Age group:
  • Can occur at any age, but common in infants and preschool-aged children.
  • Frequently seen in nurseries, households with overcrowding, and institutional settings.
• Transmission:
  • Spread through prolonged skin-to-skin contact or sharing bedding/clothing.
  • Often involves multiple household members; index case may be asymptomatic.

Diagnosis

• Clinical evaluation:
  • Diagnosis is usually clinical, based on history of intense itching and characteristic rash.
  • Enquire about other affected contacts, especially household or nursery members.
• Dermatoscopy or microscopy (if available):
  • May reveal mites, eggs, or faecal pellets in burrows.
  • Not routinely required in primary care but can support uncertain cases.

Differential diagnosis

• Eczema:
  • Chronic condition with variable pruritus and widespread distribution.
  • Less likely to present with burrows or nocturnal itch as dominant feature.
• Impetigo:
  • Honey-coloured crusting, especially on the face; often bacterial superinfection over scabies.
• Papular urticaria:
  • Hypersensitivity reaction to insect bites; papules often grouped and pruritic but not burrowed.
• Insect bites:
  • Often limited to exposed areas; pruritus may be intense but without burrows or household spread.

Red flags

• Secondary infection:
  • Presence of pustules, oozing or widespread crusting may indicate impetiginisation.
• Failure of response:
  • Persistent symptoms after appropriate treatment may suggest treatment failure or reinfestation.
• Infestation in immunocompromised host:
  • Risk of crusted scabies (Norwegian scabies), which is highly contagious and requires urgent specialist management.
• Widespread household outbreak:
  • Requires coordinated management to prevent reinfection.

Management

• Topical treatment:
  • Permethrin 5% cream: first-line treatment; applied to the whole body (including scalp and face in infants) and left on for 8–12 hours before washing off.
  • Repeat application after 7 days to target newly hatched mites.
• Alternative treatment:
  • Malathion 0.5% lotion: used if permethrin is contraindicated.
• Systemic treatment:
  • Oral ivermectin: 200 mcg/kg for 1 dose, recovery may take up to 4 weeks after treatment; only repeat the dose within 2 weeks if new lesions appear.
• Management of contacts:
  • All household and close contacts should be treated simultaneously, even if asymptomatic.
• Environment:
  • Wash bedding, clothing, and towels at ≥60°C.
  • Items that cannot be washed should be sealed in a plastic bag for 72 hours.

Patient education

• Understanding scabies:
  • Explain that symptoms result from an allergic reaction to the mites.
  • Reassure that it is treatable but may cause itch for up to 4 weeks after treatment.
• Prevention of reinfection:
  • Emphasise simultaneous treatment of close contacts and appropriate cleaning of the environment.
• When to seek help:
  • If rash persists beyond 4 weeks after treatment.
  • Signs of secondary infection (pus, oozing, fever).
  • If infants are unwell or if crusted scabies is suspected.