What is the recommended treatment for Strep anginosus infections?

Treatment of Streptococcus anginosus Infections

For Streptococcus anginosus infections, penicillin is the first-line treatment, with ceftriaxone being an appropriate alternative, and treatment duration should be at least 4 weeks for invasive infections. 1, 2

Antimicrobial Therapy Options

First-line Treatment

• Penicillin G: 12-18 million units/day IV divided in 4-6 doses or continuously for 4 weeks 1
• Amoxicillin: 100-200 mg/kg/day IV in 4-6 doses for 4 weeks 1
• Ceftriaxone: 2 g/day IV or IM in 1 dose for 4 weeks 1

For Penicillin-Allergic Patients

• Clindamycin: 600-900 mg IV every 8 hours 1, 2
• Vancomycin: 15-20 mg/kg IV every 12 hours (for severe infections) 1, 3

Treatment Duration and Considerations

Duration of Therapy

• Invasive infections (endocarditis, abscesses): Minimum 4 weeks 1
• Localized infections (pharyngitis): 10 days 4
• Empyema/abscess: 2-4 weeks, often requiring surgical drainage 5, 6

Special Considerations

1. Abscess Formation: S. anginosus group has a propensity to form abscesses, requiring:

   • Surgical drainage in addition to antibiotics 6
   • Blood cultures every 24-48 hours until clearance 1

2. Monitoring Treatment Response:

   • If operative tissue cultures are positive, complete a full antimicrobial course after surgery 1
   • If operative tissue cultures are negative, count pre-surgical antibiotic days toward total duration 1

3. Combination Therapy:

   • For severe infections, adding gentamicin (3 mg/kg/day IV) may provide synergistic killing 1
   • Not recommended for routine cases due to nephrotoxicity risk

Clinical Pearls and Pitfalls

Important Clinical Considerations

• S. anginosus group (formerly S. milleri) includes S. anginosus, S. intermedius, and S. constellatus
• These organisms are part of normal oral, gastrointestinal, and genitourinary flora
• Unlike other viridans streptococci, they frequently cause invasive, purulent infections 1, 6

Common Pitfalls

1. Failure to identify distant abscesses: Always evaluate for metastatic infection sites (brain, liver, lung) 6
2. Inadequate duration: Shorter courses often lead to treatment failure 7
3. Misidentification: Laboratory systems may misidentify the organism, leading to inappropriate treatment 3
4. Inadequate surgical intervention: Antibiotics alone are often insufficient; drainage procedures are frequently necessary 5, 6

Infectious Disease Consultation

• Infectious disease consultation is strongly recommended to define optimal empirical treatment regimen at initiation of antimicrobial therapy 1

By following these guidelines, clinicians can effectively manage S. anginosus infections while minimizing complications and treatment failures.