What is the diagnosis and treatment for a 7-year-old child presenting with a sore throat and a rash on the bilateral buttocks?

Diagnosis: Scarlet Fever (Group A Streptococcal Pharyngitis with Scarlatiniform Rash)

This 7-year-old child presenting with sore throat and raised red papules (capsules) scattered across bilateral buttocks has scarlet fever, which is Group A streptococcal (GAS) pharyngitis with a characteristic scarlatiniform rash, and requires immediate confirmation with rapid antigen detection testing (RADT) or throat culture followed by antibiotic treatment with penicillin or amoxicillin for 10 days. 1

Clinical Presentation Analysis

The combination of sore throat with a raised red rash on the buttocks in a 7-year-old is highly suggestive of scarlet fever, which occurs when GAS pharyngitis is accompanied by a scarlatiniform rash. 1

Key diagnostic features present in this case:

• Age 5-15 years: This is the peak age group for GAS pharyngitis, with prevalence of 20-30% in symptomatic children 1
• Sore throat: Classic presenting symptom of GAS pharyngitis 1
• Scarlatiniform rash: The raised red "capsules" (papules) scattered on the buttocks represent the characteristic sandpaper-like rash of scarlet fever, which can appear on the trunk, extremities, and buttocks 1, 2

Important caveat: The rash in scarlet fever typically follows the onset of other symptoms by 1-2 days in 71% of cases, so the temporal sequence matters for diagnosis 2

Immediate Diagnostic Approach

Perform RADT or throat culture immediately - do not treat based on clinical features alone, as viral pharyngitis can mimic bacterial infection. 1

• Swab both the posterior pharyngeal wall and tonsils for maximum yield 1
• A positive RADT is diagnostic and does not require backup culture (specificity ≥95%) 1
• Critical for children: If RADT is negative, send a backup throat culture because RADT sensitivity is only 80-90%, missing 10-20% of true GAS infections 1, 3

Do not delay testing even with classic scarlatiniform rash present, as confirmation prevents overtreatment of viral mimics and documents the infection. 1

First-Line Treatment

Once GAS pharyngitis is confirmed (either by positive RADT or positive culture):

Penicillin V or Amoxicillin for 10 days (strong recommendation, high-quality evidence): 1

• Amoxicillin: 50 mg/kg once daily (maximum 1000 mg) for 10 days, OR 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1
• Penicillin V: 250 mg twice or three times daily for 10 days 1

Rationale for choosing amoxicillin in this age group: Better palatability and availability as suspension makes amoxicillin preferable to penicillin V in younger children, with equivalent efficacy. 1, 4

Alternative Antibiotics (If Penicillin Allergic)

For non-anaphylactic penicillin allergy:

• Cephalexin: 20 mg/kg/dose twice daily (maximum 500 mg/dose) for 10 days 1, 5
• Cefadroxil: 30 mg/kg once daily (maximum 1 g) for 10 days 1, 5

For anaphylactic penicillin allergy:

• Clindamycin: 7 mg/kg/dose three times daily (maximum 300 mg/dose) for 10 days 1, 5
• Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days (note: geographic resistance varies) 1, 5
• Clarithromycin: 7.5 mg/kg/dose twice daily (maximum 250 mg/dose) for 10 days 1, 5

Adjunctive Symptomatic Treatment

Provide analgesic/antipyretic therapy for symptom relief and fever control: 1

• Acetaminophen or ibuprofen (strong recommendation, high-quality evidence) 1
• Avoid aspirin in children due to risk of Reye syndrome (strong recommendation, moderate-quality evidence) 1
• Do not use corticosteroids - not recommended for routine GAS pharyngitis (weak recommendation, moderate-quality evidence) 1

Critical Management Points

Treatment prevents acute rheumatic fever when initiated within 9 days of symptom onset, so even if culture results are pending, treatment can be started once positive confirmation is obtained. 1, 3

Do not test or treat household contacts unless they develop symptoms - asymptomatic carriage is common (up to one-third of households) and prophylactic antibiotics are not effective. 1, 3

No follow-up testing needed if the child becomes asymptomatic after completing treatment - post-treatment cultures are not routinely recommended as they cannot distinguish carriers from active infection. 1, 3

Common Pitfalls to Avoid

Do not diagnose scarlet fever based on rash appearance alone - the rash can be subtle or absent initially, and viral exanthems can mimic scarlatiniform rash. Always confirm with RADT or culture. 1

Do not miss the diagnosis in older children presenting primarily with sore throat - scarlet fever may be overlooked in children aged 5+ who present with prominent pharyngitis, as clinicians may attribute symptoms to viral infection. 2

Do not use broad-spectrum antibiotics like amoxicillin-clavulanate as first-line therapy - narrow-spectrum penicillin or amoxicillin is preferred to minimize resistance and adverse effects. 1, 4

Do not treat without microbiological confirmation - up to 70-80% of sore throats in this age group are viral, and clinical features alone cannot reliably distinguish GAS from viral pharyngitis. 1, 3