What are the characteristics and treatment of scarlet fever in a patient presenting with fever and rash, possibly following a streptococcal infection or sore throat?

Scarlet Fever: Clinical Characteristics and Management

Scarlet fever is a Group A streptococcal (GAS) pharyngitis accompanied by a distinctive sandpaper-like rash caused by streptococcal pyrogenic exotoxins, requiring immediate microbiological confirmation and 10 days of oral penicillin V to prevent rheumatic fever and other serious complications. 1, 2

Clinical Presentation

Pathognomonic Features

• The hallmark sandpaper-textured, papular rash typically begins on the trunk and spreads to extremities with characteristic accentuation in the perineal region 1, 2
• "Strawberry tongue" is pathognomonic and frequently accompanies the rash 1
• The rash appears earlier in the illness compared to other exanthems and rarely becomes petechial, with early desquamation possible 2

Associated Pharyngeal Findings

• Sudden-onset severe sore throat with pain on swallowing 3, 1
• High fever typically ranging from 101-104°F (38.3-40°C) 3, 4
• Tonsillopharyngeal erythema with or without exudates 3, 1
• Tender, enlarged anterior cervical lymph nodes 3, 1
• Soft palate petechiae ("doughnut" lesions) 3
• Beefy red, swollen uvula 3, 1

Systemic Symptoms

• Headache, nausea, vomiting, and abdominal pain—particularly common in pediatric patients 3, 1

Epidemiology

• Primarily affects children aged 5-15 years, though cases occur at all ages 1, 5
• Peak incidence in winter and early spring in temperate climates 3, 1
• History of exposure to documented streptococcal infection increases likelihood 2

Diagnostic Approach

When to Test

Perform microbiological testing when clinical and epidemiological features suggest GAS pharyngitis, but NOT when viral features predominate 3, 2

Test if present:

• Sudden-onset sore throat with high fever 3
• Scarlatiniform rash with sandpaper texture 1
• Absence of viral symptoms (coryza, hoarseness, cough, conjunctivitis, diarrhea) 3, 2

Do NOT test if present:

• Viral features: conjunctivitis, coryza, cough, hoarseness, discrete ulcerative stomatitis, viral exanthem 3, 2
• Generally avoid testing in children under 3 years unless risk factors present (e.g., older sibling with illness) 2

Microbiological Confirmation (Mandatory)

Clinical features alone cannot definitively diagnose GAS infection—microbiological confirmation is mandatory before initiating antibiotics 1, 4

Testing algorithm:

1. Perform rapid antigen detection test (RADT) first 2, 4
2. In children and adolescents with negative RADT, obtain backup throat culture (gold standard) 1, 2, 4
3. In adults with negative RADT, backup culture generally not necessary due to low rheumatic fever risk, though can be considered 2

Specimen collection technique:

• Vigorously swab both tonsils and posterior pharynx 3
• Throat culture remains the reference standard for confirming GAS pharyngitis 2

Critical Diagnostic Pitfall

Asymptomatic GAS carriers (up to 15% of school-age children in winter/spring) may have positive throat cultures during concurrent viral pharyngitis, mimicking acute infection 3, 2. Clues to differentiate include presence of viral features and lack of sudden onset 2.

Treatment

First-Line Antibiotic Therapy

Oral Penicillin V (phenoxymethylpenicillin) 250-500 mg every 6-8 hours for 10 days 2, 4, 6

• Alternative dosing: 500 mg twice daily or 250 mg three times daily 2
• Completing the full 10-day course is critical—shorter durations lack evidence 2
• Therapy must be sufficient to eliminate the organism to prevent sequelae of streptococcal disease 6

Alternative Regimens

For non-anaphylactic penicillin allergy:

• First-generation cephalosporins 2, 4

For true penicillin allergy (anaphylactic):

• Macrolides (azithromycin), though be aware some strains are resistant 2, 7
• Susceptibility testing should be performed when using macrolides 7
• Data establishing efficacy of azithromycin in preventing rheumatic fever are not available 7

Co-amoxiclav considerations:

• May be considered only for documented treatment failure with penicillin (uncommon) 2
• Children: 40 mg/kg/day of amoxicillin component in 2-3 divided doses for 10 days 2
• Adults: 500 mg twice daily for 10 days 2
• Higher rates of gastrointestinal side effects (diarrhea) compared to penicillin 2
• Not recommended as first-line due to broader spectrum and higher resistance risk 2

Never use:

• Sulfonamide antibiotics—associated with increased disease severity and mortality 2
• Aspirin in children under 16 years—risk of Reye's syndrome 2

Timing and Infectivity

• Antibiotics can be started up to 9 days after symptom onset and still prevent rheumatic fever 2, 4
• Patient becomes non-contagious after 24 hours of antibiotic therapy 2, 4
• Early treatment reduces infectivity period and morbidity 2

Symptomatic Management

• Antipyretics (ibuprofen or acetaminophen) for fever and pain relief 2
• Antipyretics do not replace the need for antibiotics 2

Monitoring and Follow-Up

• Monitor for clinical improvement within 48-72 hours of starting antibiotics 2
• If symptoms persist beyond 3-5 days of antibiotic therapy, reassess the diagnosis and consider alternative pathogens 2
• Post-treatment throat cultures not routinely recommended unless symptoms persist or recur 2
• Cultures should be taken following completion of treatment to determine if streptococci have been eradicated 6

Management of Close Contacts

• Routine throat cultures or treatment for asymptomatic household contacts generally not necessary 2
• In outbreak situations, perform throat cultures for all patients and treat only those with positive cultures 2
• Exception: Obtain throat swabs from all household contacts of a child with acute rheumatic fever and treat if positive 3

Infection Control

• Isolate patients for minimum of 24 hours of effective antibiotic therapy 2
• Healthcare workers must use disposable gloves and aprons with strict hand hygiene before and after patient contact 2

Complications if Untreated

Early antibiotic treatment is essential to prevent serious sequelae 2:

• Suppurative complications: peritonsillar abscess 2
• Non-suppurative complications: acute rheumatic fever, acute glomerulonephritis 2
• Other potential complications: bacteremia, pneumonia, endocarditis, meningitis 5

Common Clinical Pitfalls

• Relying on clinical features alone without microbiological confirmation 1, 4
• Testing patients with predominantly viral symptoms, leading to unnecessary antibiotic use 3, 2
• Failing to obtain backup throat culture after negative RADT in children/adolescents 1, 2
• Not completing the full 10-day antibiotic course, which may decrease effectiveness and promote resistance 2, 6
• Misdiagnosing asymptomatic GAS carriers with viral pharyngitis as acute scarlet fever 3, 2
• Underestimating severity in adults—while primarily a childhood disease, adults can develop severe complications including airway emergencies 8, 9