Scarlet Fever

BASICS

Definition: A childhood disease characterized by fever, pharyngitis, and a "sandpaper" rash, caused by group A β-hemolytic Streptococcus pyogenes (GAS) producing erythrogenic toxin.
Incubation: 1–7 days; illness duration 4–10 days.
Key Features: Rash appears 24–48 hours after symptom onset, begins in groin/trunk/axillae, spreads to extremities, spares palms/soles. Strawberry tongue and circumoral pallor are classic.
Rash: Erythematous, blanchable, 1–2 mm papules, clears by end of week 1, followed by weeks of desquamation.

Incidence: 15% of school-aged children, 4–10% of adults have an episode of GAS pharyngitis yearly.
Peak Age: 4–8 years (common 6–12 years), rare in >12 years.
Sex: Male = female.
Prevalence: 15–30% of pharyngitis cases in children due to GAS; <10% of children with GAS pharyngitis develop scarlet fever.
Seasonality: Winter/early spring.
Transmission: Airborne respiratory droplets, saliva, nasal secretions; rare foodborne outbreaks.

Pathogen: GAS producing erythrogenic toxin (types A, B, C).
Mechanism: Toxins damage capillaries (rash) and act as superantigens.
Immunity: Antitoxin antibodies prevent rash but not infection.
Primary Infection Sites: Usually tonsils, but also skin, surgical wounds, uterus.

School-aged children, winter/early spring, contact with infected individuals, crowded conditions.

Exclude afebrile children from school/daycare until 24h after starting antibiotics.
Symptomatic contacts should be tested and treated if positive.
Asymptomatic contacts do not require cultures/prophylaxis.

Suppurative: Pharyngitis, impetigo, otitis media, sinusitis, abscesses, pneumonia.
Nonsuppurative: Rheumatic fever, glomerulonephritis.

Prodrome: 1–2 days of sore throat, headache, myalgia, malaise, fever (>38°C), vomiting, abdominal pain.
Rash: Scarlatiniform, punctate, erythematous, appears after 24–48h, spreads rapidly.

Oral: Beefy red tonsils/pharynx, palatal petechiae, white (early) then red strawberry tongue, circumoral pallor.
Rash: Scarlet, sandpaper texture, blanches, initially groin/axilla/trunk, spreads to extremities, spares palms/soles.
Other: Pastia lines (transverse red streaks at skin folds), flushed face, desquamation after 7–10 days (starts on face, then trunk/hands/feet), vesicles in severe cases.

Viral exanthems (measles, rubella, roseola, fifth disease), mono, mycoplasma, TSS, staphylococcal scalded-skin syndrome, Kawasaki, lupus, juvenile arthritis, drug rash, sunburn.

Rapid antigen detection test (RADT) / PCR: Confirm GAS. In children, negative RADT should be confirmed by throat culture. Positive RADT or PCR is diagnostic.
Throat culture: Gold standard for GAS (99% specificity, 90–97% sensitivity).
Modified Centor score: Clinical decision rule for likelihood of GAS pharyngitis.
Serologic tests: Not recommended for acute diagnosis.
CBC: May show leukocytosis.
Gram stain: Gram-positive cocci in chains.

Supportive: analgesics/antipyretics (acetaminophen/NSAIDs), throat lozenges, topical anesthetics.
Exclude aspirin in children (Reye syndrome risk).

Penicillin V: 10 days (children <27 kg: 250 mg BID/TID; >27 kg/adults: 250 mg QID or 500 mg BID).
Benzathine penicillin G: Single IM dose (<27 kg: 600,000 U; >27 kg: 1.2 million U) for compliance issues.
Amoxicillin: 50 mg/kg (max 1,000 mg) once daily or 25 mg/kg (max 500 mg) BID for 10 days (preferred in children).

Full course of antibiotics is essential.
Delayed antibiotics (up to 10 days after symptoms start) still prevent rheumatic fever.
Rash is not dangerous; marker of GAS infection.

Treatment shortens symptoms by 1–2 days, reduces complications and contagiousness.
Desquamation may last weeks.
Recurrent attacks possible (different toxin types).

Suppurative: Sinusitis, otitis, mastoiditis, cervical adenitis, abscesses, pneumonia, bacteremia, meningitis, septic arthritis, endocarditis, necrotizing fasciitis.
Nonsuppurative: Rheumatic fever (preventable if antibiotics within 10 days), glomerulonephritis (not clearly prevented by antibiotics), toxic shock, PANDAS, poststreptococcal reactive arthritis.
Other: Nail grooves, telogen effluvium (hair loss), scarlet fever may rarely cause severe complications.

Suspect scarlet fever in children with fever and exanthematous rash.
Classic findings: strawberry tongue, circumoral pallor, coarse sandpaper rash, Pastia lines.
Penicillin (or amoxicillin in children) remains the treatment of choice.
Use Centor score and rapid testing to guide diagnosis.
Desquamation after 7–10 days is characteristic and can last weeks.