Scarlet fever

Scarlet fever is an acute syndrome caused by Streptococcus pyogenes, a highly contagious toxin-producing group A Streptococcus (GAS). The syndrome most commonly occurs in children and in less than 10% of patients with streptococcal tonsillopharyngitis. Scarlet fever classically manifests with fever, pharyngeal erythema, flushed cheeks with perioral pallor, strawberry tongue, and an erythematous rash with sandpaper-like texture. Desquamation of the face, trunk, hands, fingers, and toes begins approx. one week after the rash resolves. Antibiotic treatment with penicillin is recommended as scarlet fever may progress to severe disease and lead to complications (e.g., rheumatic fever and poststreptococcal glomerulonephritis). Recurrent infection with other toxins may occur as S. pyogenes produces several types of erythrogenic toxins.

• Peak incidence: 5–15 years (although it may affect individuals of any age) [1]
• Generally occurs in association with streptococcal cases of tonsillopharyngitis

Epidemiological data refers to the US, unless otherwise specified.

• Pathogenic
  • Group A Streptococcus (i.e., S. pyogenes) produces erythrogenic exotoxin A, B, and/or C.
  • Previous infection does not rule out additional episodes of the disease as there are several different types of scarlet fever toxin.
• Route of transmission: aerosol
• Incubation period: 2–5 days [2]

References:[3]

Prodrome [2]

• Fever
• Symptoms of tonsillopharyngitis, e.g.:
  • Sore throat and difficulty swallowing
  • Pharyngeal erythema, possibly with tonsillar exudates
  • Enlarged cervical lymph nodes
• Abdominal pain, nausea, and/or vomiting [4]

Rarely, scarlet fever develops after a streptococcal skin and soft tissue infection rather than tonsillopharyngitis. [2]

Exanthem phase [5]

• Rash manifests 12–48 hours after fever onset. [6]
• Fine, erythematous, sandpaper‑like texture
• Blanches with pressure, but nonblanching petechiae may also be present
• Often pruritic
• Begins on neck or trunk and spreads rapidly across the body (except for the palms and soles)
• Characteristic features include:
  • Flushed cheeks with perioral pallor
  • Strawberry tongue: bright red tongue color with papillary hyperplasia, which may initially be covered with a white coating
  • Pastia lines
    • A characteristic sign of scarlet fever
    • Linear, petechial appearance
    • Most pronounced in the groin, underarm, and elbow creases (i.e., flexural areas)
• Lasts ∼ 7 days [1]

Findings such as coryza, rhinorrhea, cough, hoarseness, anterior stomatitis, conjunctivitis, and ulcerative lesions are atypical for scarlet fever and warrant further investigation.

Desquamation phase [5]

• Desquamation; begins 7–10 days after rash resolves. [7]
• Most affected areas include the face, skin folds, hands, and feet.
• Lasts up to 4–6 weeks [5]

Scarlet fever can rarely occur after nonpharyngeal infection; for management in those cases, see “Impetigo” and/or “Nonpurulent skin and soft tissue infections.”

Confirmatory tests [1][2]

Scarlet fever has characteristic clinical features, but the diagnosis must be confirmed with one of the following laboratory studies. For acute pharyngitis without the other clinical features of scarlet fever, see “Diagnosis of acute pharyngitis.”

• Throat culture for GAS (gold standard)
• Rapid antigen detection testing (rapid strep test)
  • Positive test: Treat as scarlet fever.
  • Negative test
    • Adults: No further testing is routinely required.
    • Children > 3 years of age: Obtain a throat culture for GAS.
    • Children ≤ 3 years of age: Consider obtaining a throat culture for GAS. [1][2][8]
• NAAT from a throat swab [2]
• Delayed presentation with nonsuppurative complications of GAS infection: antistreptolysin O (ASO) and anti-DNase B (ADB) titers [8][9]

Blood tests are not routinely recommended as common findings (e.g., leukocytosis, raised inflammatory markers) are nonspecific. [10]

• Other infectious rashes in childhood
• Drug hypersensitivity reaction
• Chickenpox (varicella)
• Kawasaki disease
• Viral tonsillitis (infectious mononucleosis, herpangina)

The differential diagnoses listed here are not exhaustive.

Scarlet fever can rarely occur after nonpharyngeal infection; for management in those cases, see “Impetigo” and/or “Nonpurulent skin and soft tissue infections.”

• Initiate one of the recommended antibiotic regimens for acute GAS pharyngitis, e.g.: [1][2]
  • Oral penicillin V or amoxicillin
  • Nonsevere penicillin reaction: oral cephalosporins (e.g., cephalexin)
  • Severe penicillin reaction: oral macrolides (e.g., azithromycin) or clindamycin
• Recommend supportive care for sore throats.
• Isolation recommendations [1][2]
  • Hospitalized patients: Maintain droplet precautions for 24 hours after initiating antibiotic therapy.
  • Advise outpatients to isolate until they:
    • Are afebrile
    • Have been taking antibiotic therapy for at least 12–24 hours

Antibiotic therapy reduces symptom duration, infectiousness, and risk of developing complications of scarlet fever. [1]

• Scarlet fever is considered a nonsuppurative (i.e., non-pus-forming) complication of streptococcal tonsillopharyngitis.
• Other complications of GAS tonsillopharyngitis may occur during or after scarlet fever, especially in patients who did not receive antibiotic therapy. E.g.:
  • Nonsuppurative complications of GAS infection (e.g., poststreptococcal glomerulonephritis, acute rheumatic fever)
  • Suppurative complications of acute tonsillopharyngitis (e.g., retropharyngeal abscess, peritonsillar abscess)

We list the most important complications. The selection is not exhaustive.