What is the appropriate treatment for a suspected Group A Streptococcal (GAS) infection presenting as a rectal rash?

Treatment of Perianal Group A Streptococcal Infection

For a suspected Group A Streptococcal (GAS) infection presenting as a rectal/perianal rash, treat with oral amoxicillin 50 mg/kg/day divided twice daily for a full 10 days. 1

Confirming the Diagnosis

Before initiating antibiotics, you should obtain a culture from the perianal area to confirm GAS infection, as clinical appearance alone cannot reliably distinguish bacterial from other causes of perianal dermatitis. 1 Perianal GAS infections in children typically present with:

• Perianal erythema and tenderness
• Painful defecation
• Blood-streaked stools
• Pruritus
• Well-demarcated erythematous rash around the anus 1

First-Line Treatment Regimen

Amoxicillin is the preferred first-line agent with dosing of 50 mg/kg/day divided into two doses (maximum 500 mg per dose) for 10 days. 1 This provides equivalent efficacy to penicillin V but offers better palatability for young children and is available as a suspension. 1, 2

The full 10-day course is mandatory to achieve maximal bacterial eradication and prevent potential complications, including the theoretical risk of acute rheumatic fever, even though this complication is more commonly associated with pharyngeal GAS infections. 1, 2

Alternative Regimens for Penicillin Allergy

For Non-Immediate Penicillin Allergy (Delayed Rash, No Anaphylaxis)

Use first-generation cephalosporins as the preferred alternative:

• Cephalexin: 20 mg/kg per dose twice daily (maximum 500 mg/dose) for 10 days 1
• Cross-reactivity risk is only 0.1% in patients with non-severe, delayed penicillin reactions 3

For Immediate/Anaphylactic Penicillin Allergy

Avoid all beta-lactams due to 10% cross-reactivity risk. 3, 1 Use instead:

• Clindamycin: 7 mg/kg per dose three times daily (maximum 300 mg/dose) for 10 days 1

  • Preferred choice with only ~1% resistance among GAS in the United States 3
  • Demonstrates high efficacy even in chronic carriers 3

• Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days 1

  • Only antibiotic requiring just 5 days due to prolonged tissue half-life 3
  • However, macrolide resistance is 5-8% in the United States 3

Critical Pitfalls to Avoid

Never use trimethoprim-sulfamethoxazole (Bactrim), tetracyclines, or sulfonamides for GAS infections—these agents fail to eradicate streptococci effectively and are absolutely contraindicated. 1

Do not shorten the antibiotic course below 10 days (except for azithromycin's 5-day regimen), as this dramatically increases treatment failure rates and risk of complications. 1 Even if symptoms resolve in 3-4 days, the full course is essential for bacterial eradication. 4

Do not assume all penicillin-allergic patients cannot receive cephalosporins—only those with immediate/anaphylactic reactions (hives, angioedema, bronchospasm within 1 hour) should avoid them. 1, 4

Adjunctive Symptomatic Management

Consider acetaminophen or ibuprofen for pain and discomfort associated with the perianal infection. 1 Avoid aspirin in children due to Reye syndrome risk. 3

Sitz baths with warm water may provide symptomatic relief for perianal discomfort, though this is based on general clinical practice rather than specific GAS treatment guidelines.

When to Consider Treatment Failure

If symptoms persist or worsen after 48-72 hours of appropriate antibiotic therapy, consider:

• Non-compliance with medication
• Resistant organism (though GAS remains universally susceptible to penicillin)
• Alternative or concurrent diagnosis
• Need for culture-directed therapy adjustment 1

For recurrent perianal GAS infections after completing appropriate therapy, clindamycin or amoxicillin-clavulanate may be more effective at eradicating chronic carriage. 5