Scarlet Fever

Scarlet fever is an acute illness caused by Group A Streptococcus (Streptococcus pyogenes) producing erythrogenic (pyrogenic) exotoxins that trigger a characteristic diffuse rash and systemic symptoms. It most often follows streptococcal pharyngitis in school‑aged children but can complicate skin/soft‑tissue infections.

Epidemiology & Transmission

• Peak age: 5–15 years; outbreaks in schools, households.
• Spread: respiratory droplets, close contact, shared utensils; incubation 2–5 days (range 1–7).

Pathogenesis (Brief)

Toxin‑mediated type IV (delayed) hypersensitivity and superantigen effects produce diffuse capillary dilation (scarlatiniform rash) and systemic symptoms. Immune responses also underlie delayed nonsuppurative complications (rheumatic fever, glomerulonephritis).

Classic Clinical Stages

1. Prodrome: acute onset fever, sore throat, headache, abdominal pain, vomiting; tonsillopharyngeal erythema +/- exudates; tender anterior cervical nodes.
2. Exanthem (rash stage): within 12–48 h of fever. Diffuse, blanching, finely punctate “sandpaper” erythema starting on trunk/neck, spreading to extremities; accentuated in flexural creases (Pastia lines). Circumoral pallor contrasts with flushed cheeks.
3. Desquamation: begins 1–3 weeks later—peeling of fingertips, toes, groin, and axillae, sometimes sheets from palms/soles.

Key Physical Findings

• Strawberry tongue: early white coating with prominent papillae (“white strawberry”), later bright red (“red strawberry”).
• Pharyngeal erythema; petechiae on soft palate possible.
• Sandpaper rash spares palms and soles (until desquamation phase).
• Mild hepatosplenomegaly possible; generalized tender lymphadenopathy.

Differential Diagnosis

• Viral exanthems (adenovirus, enterovirus), measles, rubella.
• Drug eruptions.
• Staphylococcal scalded skin syndrome.
• Kawasaki disease (look for prolonged fever ≥5 days, conjunctivitis, extremity changes, mucous membrane changes, cervical lymph node ≥1.5 cm).
• Toxic shock syndromes.

Laboratory Diagnosis

• Confirm GAS: rapid antigen detection test (RADT) or throat culture. Culture remains reference, especially if RADT negative in children with high suspicion.
• CBC: mild leukocytosis; inflammatory markers may be elevated.
• Anti‑streptococcal antibody titers (ASO, anti‑DNase B) are retrospective (not for acute management).

Complications

Suppurative: peritonsillar/retropharyngeal abscess, otitis media, sinusitis, cervical lymphadenitis, pneumonia.
Nonsuppurative: acute rheumatic fever, post‑streptococcal glomerulonephritis, scarlet nephritis (rare), reactive arthritis, pediatric autoimmune neuropsychiatric disorders (PANDAS — controversial).

Treatment

Goals: eradicate organism, shorten symptoms modestly, prevent transmission and rheumatic fever.

First‑line (if no penicillin allergy):
– Penicillin V orally for 10 days OR
– Amoxicillin (palatability, similar efficacy) 10 days.

If adherence concern: single IM benzathine penicillin G (weight‑based dosing).

Penicillin allergy (non‑anaphylactic): first‑generation cephalosporin (e.g., cephalexin) 10 days.
Immediate (IgE‑mediated) allergy: macrolide (azithromycin 5 days, clarithromycin 10 days) or clindamycin (10 days) guided by local resistance.

Supportive care: hydration, antipyretics (acetaminophen/ibuprofen), soft diet, throat lozenges (age‑appropriate). Avoid aspirin in children.

Reevaluate if no improvement after 48–72 h of appropriate therapy—consider alternative diagnoses, abscess, or antimicrobial resistance.

Infection Control

• Exclude from school/daycare until at least 24 h of appropriate antibiotics and afebrile.
• Practice strict hand hygiene, avoid sharing utensils.
• Replace or sterilize toothbrush after 24–48 h of therapy.

Prevention & Follow‑Up

• Prompt treatment of streptococcal pharyngitis reduces rheumatic fever risk.
• Routine prophylaxis for contacts not required unless outbreaks with high risk individuals.
• Monitor for late signs: hematuria/edema (possible glomerulonephritis), migratory polyarthritis/carditis (rheumatic fever) weeks later.

Red Flags — Seek Urgent Care

• High persistent fever, neck swelling, trismus (possible deep neck space infection).
• Respiratory distress, drooling (airway compromise).
• Severe abdominal pain (possible mesenteric adenitis/intussusception mimic).
• Hematuria, edema, new joint pains in convalescence.

Quick Summary Table

• Incubation: 2–5 days.
• Hallmark: sandpaper rash + strawberry tongue + Pastia lines + circumoral pallor.
• Test: RADT/culture before antibiotics (unless already confirmed in an outbreak context).
• Therapy: 10 days penicillin/amoxicillin (or single IM benzathine penicillin G).
• Follow‑up: watch for desquamation and late immune complications.

Educational information only; seek medical evaluation for suspected scarlet fever or worsening symptoms.