Should Methicillin-resistant Staphylococcus aureus (MRSA) screening be performed on Intravenous (IV) drug abusers presenting with abscesses?

MRSA Screening for IV Drug Abusers with Abscesses

Yes, MRSA screening should be performed on IV drug abusers presenting with abscesses to guide appropriate antimicrobial therapy, as this population has high rates of MRSA colonization and infection. 1

Rationale for MRSA Screening

• IV drug users have significantly higher rates of MRSA colonization compared to non-drug users, with studies showing increasing prevalence of MRSA in this population 1
• The microbiology of abscesses in IV drug users has shifted over time, with MRSA becoming increasingly prevalent - from 5% of S. aureus infections in 1999 to 82% in 2005 2
• IV drug users with MRSA colonization have a 58% risk of developing MRSA infection, making identification crucial for appropriate treatment 1

Microbiology of Abscesses in IV Drug Users

• While Staphylococcus aureus remains the most common pathogen in IV drug user abscesses (52% of cases), the proportion of MRSA has increased dramatically 2
• Infections in IV drug users are frequently polymicrobial (47-53% of cases), often including:
  • Streptococcal species (37-53% of cases) 2, 3
  • Anaerobic bacteria (10-29% of cases) 4, 2
• This microbial profile differs from non-IV drug users, who have higher rates of S. aureus (75% vs 55%) and lower rates of streptococci and anaerobes 4

Management Algorithm for IV Drug User Abscesses

1. Initial Assessment:

   • Obtain cultures from all abscesses before starting antibiotics 5
   • Perform MRSA screening via nasal swab (highest yield site) 1
   • Consider blood cultures if systemic symptoms present 6

2. Surgical Management:

   • Perform incision and drainage as primary intervention for all abscesses 5, 7
   • Ensure complete drainage of all loculations 6

3. Empiric Antibiotic Selection (pending culture results):

   • For non-severe infections:

     • Trimethoprim-sulfamethoxazole (TMP-SMX), doxycycline, or clindamycin for MRSA coverage 5
     • Consider adding coverage for streptococci if treating with TMP-SMX 5

   • For severe infections or systemic symptoms:

     • Vancomycin (15 mg/kg IV q8-12h) or linezolid (600 mg IV/PO q12h) 5, 8
     • Consider adding coverage for anaerobes (e.g., metronidazole) based on local patterns 4

4. Adjust Therapy Based on Culture Results:

   • If MRSA positive: Continue MRSA-targeted therapy 5
   • If MSSA positive: Narrow to oxacillin, nafcillin, or cefazolin 5
   • If polymicrobial: Ensure coverage for all significant pathogens 4

Pitfalls and Caveats

• Classical signs of infection (fever, leukocytosis) may be absent in IV drug users with abscesses - only 42% present with fever and 54% with leukocytosis 7
• Empiric antibiotic regimens are often discordant with guidelines in over 50% of cases, and 14% lack MRSA coverage when MRSA is present 4
• IV drug users should be screened for concomitant bloodborne infections (HIV, HBV, HCV) 6, 7
• Consider addiction treatment referral to prevent recurrence 6

Special Considerations

• Incision and drainage alone may be sufficient for small, uncomplicated abscesses, but antibiotics are recommended for:

  • Extensive or severe infections
  • Systemic symptoms
  • Immunocompromised patients
  • Areas of significant inflammation 5

• Duration of therapy should typically be 5-10 days, based on clinical response 5