🦠 Skin Infections & Viral Exanthem

🔑 Key Learning

Viral exanthems present with characteristic rashes and systemic symptoms; quarantine advice varies depending on the condition
Chickenpox and shingles are caused by VZV; shingles affects a single dermatome and doesn't cross the midline
Measles and rubella are highly contagious and require exclusion periods after rash onset
Erythema infectiosum (slapped cheek) is not infectious once rash appears, but poses risks to pregnant women
Scarlet fever presents with classic features including strawberry tongue and sandpaper rash; treat with penicillin
Bacterial and parasitic infections such as impetigo, scabies, and head lice have specific treatments and variable exclusion advice

✨ Itchy macules → papules → vesicles → crusting in crops
Rash begins on face/trunk and spreads to limbs
Exclusion: Until all vesicles have crusted (approx. 5 days after rash)

Reactivation of VZV in dorsal root ganglia
Prodrome: Dermatomal 'burning' pain
Rash: Dermatomal vesicles, unilateral, doesn't cross midline
Management:
- Oral antivirals (aciclovir) within 72h if age >50, non-truncal, immunocompromised, or severe pain
- Pain control: Paracetamol + NSAID/codeine → if ineffective, consider amitriptyline/gabapentin if needed

Prodrome: Irritable, conjunctivitis, Koplik spots (grain of salt appearance on buccal mucosa)
Rash: Morbilliform, starts behind ears → trunk - maculopapular 'blotchy' rash.
Exclusion: 4 days after rash onset

"Slapped cheek" rash, spreads to arms/body
Rash may reappear when warm (e.g. bath time), lasts weeks
Pregnancy risks: foetal anaemia, hydrops fetalis
- Exposed pregnant women should be informed to see their GP/midwife. Check bloods:
  - Recent or current infection is indicated by IgM positive - refer to specialist for close foetal monitoring, growth scans to observe for the above complications.
  - IgG and IgM both negative - not immune and therefore susceptible to infection
  - IgG positive & IgM negative - immune - reassure of immunity
Exclusion: Not required once rash appears

4 S's: Sore throat, Strawberry tongue, Sandpaper rash, 'S'ircumoral pallor
Pastia’s lines - accentuated redness in the flexor creases - axilla, inguinal folds, elbows etc.
Management: Phenoxymethylpenicillin (Pen V) for 10 days
Exclusion: 24h after starting antibiotics

Most commonly on the face, around the mouth or on the extremities
Macule develops into pustule/vesicle which then ruptures. The fluid dries forming a golden, honey-coloured crust, referred to as ‘cornflake lesions'
Lesions are itchy, sometimes painful
Impetigo can be bullous with blisters/vesicles
Management:
- Non-bullous: 1st line - Hydrogen peroxide
  - Alternative: fusidic acid/mupirocin
  - Extensive disease: PO flucloxacillin
- Bullous impetigo or extensive disease / systemically unwell: Oral flucloxacillin
- Exclusion: 48h or until crusted

Intense nocturnal itch, family/close contacts affected
- Disturbs sleep
- Crowded conditions - nursing home, prison etc.
On examination
- Erythematous papules most commonly distributed in the interdigital spaces, periumbilical area, hands, wrists, axilla, buttocks etc.
- Thin, grey lines 0.5-1.0cm may be seen - the mites burrows
Management: 1st line - Permethrin 5% once weekly x2 doses, treat all contacts
- 2nd line: Malathion
Exclusion: Until first treatment completed

Chickenpox: Itchy crops of vesicles with crusting at different stages
Shingles: Painful, dermatomal rash not crossing midline
Measles: Koplik spots, sore throat, conjunctivitis, blotchy rash
Scarlet Fever: Sandpaper rash + strawberry tongue, sore throat, sircumoral pallor
Slapped cheek: Parvovirus B19 + pregnancy alert
Impetigo: Golden honey crusts - topical hydrogen peroxide if mild, PO flucloxacillin if extensive
Molluscum: Umbilicated, pearly papules
Scabies: Burrows in interdigital spaces + itch at night. 1st line: Permethrin 5%

MMR - Measles, Mumps, Rubella = 4, 5, 6
- Measles - 4 days after rash
- Mumps - 5 days after swelling
- Rubella - 6 days after rash