Scarlet Fever

Scarlet fever is a toxin mediated illness caused by group A beta haemolytic Streptococcus pyogenes (GAS) that produces streptococcal pyrogenic exotoxins (SpeA, SpeB, SpeC), usually following pharyngitis (occasionally skin or wound infection). The rash results from a hypersensitivity response to the exotoxin in a child lacking toxin neutralising antibodies.

• Epidemiology: ages 5 to 15 years; winter and spring peaks; spread by respiratory droplets and contact; incubation 1 to 4 days; infectious until 24 hours after starting appropriate antibiotics (or for 2 to 3 weeks if untreated).
• Complications:
  • Suppurative: otitis media, sinusitis, peritonsillar and retropharyngeal abscess, cervical lymphadenitis, mastoiditis, pneumonia, invasive GAS disease (bacteraemia, necrotising fasciitis, streptococcal toxic shock syndrome).
  • Non-suppurative: acute rheumatic fever (2 to 4 weeks after pharyngitis; prevented by antibiotic treatment within 9 days of onset), post-streptococcal glomerulonephritis (1 to 3 weeks), PANDAS (disputed), reactive arthritis.
• Mortality is now very low in the antibiotic era.

• Abrupt onset of fever (38.3 to 40 C), sore throat, headache, vomiting, abdominal pain, malaise.
• Pharynx: erythema, tonsillar exudate, palatal petechiae (Forchheimer spots).
• Tongue: white coating with red papillae ("white strawberry"), then red denuded tongue with prominent papillae ("red strawberry") by day 4 to 5.
• Rash 12 to 48 hours after onset: fine erythematous punctate "sandpaper" eruption beginning on the neck and upper chest, spreading to the trunk and limbs, blanching, worse in skin folds; accentuated in flexures with linear petechiae (Pastia lines); circumoral pallor with flushed cheeks; the face is spared of eruption in the perioral area; lasts 4 to 7 days.
• Desquamation: fine flaking on the face and trunk at the end of week 1, and large sheets on fingertips, palms and soles in weeks 2 to 3.
• Tender anterior cervical lymphadenopathy.
• Red flags: toxic appearance, hypotension, rigors, severe pain out of proportion (invasive disease), drooling, trismus, muffled voice (peritonsillar abscess), stridor, neck stiffness, joint swelling, dark urine and oedema (glomerulonephritis), chorea, carditis, immunocompromise, recent varicella (high risk for invasive GAS), skin infection, non-blanching purpura.

• Clinical diagnosis with throat swab confirmation: rapid antigen detection test (specificity high; confirm negative results in children by culture) and throat culture on blood agar (the reference).
• Anti-streptolysin O and anti-DNase B titres confirm recent infection but are only useful for post-streptococcal complications.
• Full blood count (leucocytosis, eosinophilia), CRP, urinalysis (if post-streptococcal glomerulonephritis suspected), blood cultures in toxic children.
• Differentials: viral exanthems, Kawasaki disease, drug eruption, staphylococcal scalded skin syndrome and toxic shock syndrome, measles, rubella, infectious mononucleosis, sunburn.

• Antibiotics to eradicate GAS, shorten illness, reduce transmission and prevent rheumatic fever and suppurative complications (start as soon as diagnosed; prevention of rheumatic fever is effective if started within 9 days):
  • Phenoxymethylpenicillin (penicillin V) orally four times daily for 10 days: ages 1 to 5 years 125 mg; 6 to 11 years 250 mg; 12 years and over 500 mg (adults 500 mg four times daily, or 1 g twice daily).
  • Alternative: amoxicillin 50 mg/kg once daily (maximum 1 g) for 10 days; or benzathine benzylpenicillin single intramuscular dose (600,000 units for under 27 kg, 1,200,000 units for 27 kg or more) when adherence is a concern.
  • Penicillin allergy (non-severe): cefalexin 25 to 50 mg/kg/day in two divided doses (maximum 500 mg twice daily) for 10 days; cefadroxil 30 mg/kg once daily (maximum 1 g) for 10 days.
  • Severe penicillin allergy: azithromycin 12 mg/kg once daily (maximum 500 mg) for 5 days; or clarithromycin 7.5 mg/kg twice daily (maximum 250 mg per dose) for 5 days; or clindamycin 7 mg/kg three times daily (maximum 300 mg per dose) for 10 days. Check local macrolide resistance.
• Supportive: fluids, paracetamol 15 mg/kg every 4 to 6 hours (maximum 4 doses in 24 hours); ibuprofen is best avoided in invasive GAS (association with necrotising infection) and in dehydration; emollients for skin; lozenges for older children.
• Exclusion from school or nursery until 24 hours after starting antibiotics. Notify the public health authority (notifiable in many countries); hand hygiene; avoid sharing utensils.
• Contacts: observe; treat symptomatic contacts and household with a positive swab; prophylaxis is not routine except in outbreaks and for those at high risk of invasive disease (decided with public health).
• Invasive or toxic shock: admit; intravenous benzylpenicillin 50 mg/kg every 4 to 6 hours (maximum 2.4 g per dose) plus clindamycin 10 to 13 mg/kg every 8 hours (maximum 900 mg per dose) for toxin suppression, and intravenous immunoglobulin 1 g/kg.
• Peritonsillar abscess: drainage plus antibiotics.
• Follow up for complications: check urine for blood and protein 2 to 3 weeks after infection if oedema, tea coloured urine or hypertension; assess for arthralgia, chorea, or carditis.