MRSA 101 Lecture Notes

Overview of Methicillin-Resistant Staphylococcus aureus (MRSA) Bacteremia

Presenter

• Russ Olmsted, MPH, CIC
• Contributions by David P. Calfee, Vineet Chopra, Kyle Popovich

Learning Objectives

• Understand the pathogenesis of MRSA bacteremia
• Outline the epidemiology of MRSA bacteremia
• Describe a tiered approach to MRSA bacteremia prevention

The Organism: MRSA

• Type: Gram-positive cocci bacteria
• Characteristic: Forms clusters under gram staining
• 30% of people are colonized with S. aureus in their nose
• MRSA is coagulase-positive
• Resistant to nearly all penicillin/beta-lactam antibiotics
• Oxacillin commonly used to detect resistance

Understanding MRSA Bacteremia

• Definition: S. aureus cultured from blood showing resistance
• Primary Sites of Infection:
  • Vascular catheter-related
  • Skin and soft tissue
  • Pneumonia
  • Surgical site
  • Endocarditis
• Up to 25% of cases have no identifiable initial infection site

Evolution of Drug Resistance in S. aureus

• History:
  • Resistance began soon after penicillin discovery
  • Methicillin resistance widespread by the 1970s
  • Vancomycin-resistant strains emerged in the 1990s

Concerns About MRSA

• Mortality Rate: 15-50% for MRSA bacteremia
• Infections:
  • 80,000 severe MRSA infections annually
  • 11,000 annual deaths
• Other HAIs: S. aureus frequently causes HAIs

MRSA Colonization and Transmission

• Transmission:
  • Via contaminated hands of healthcare personnel
  • Contaminated environmental surfaces
  • Direct contact in the community
• Colonization: Patients with MDROs often have other MDROs

MRSA Bacteremia Prevention

Tier 1: First Steps

• Complete MRSA risk assessment
• Monitor and report cases
• Hand hygiene adherence
• Use Contact Precautions
• Assess cleaning and disinfection quality

Tier 2: Enhanced Practices

• Hospital Onset MRSA needs assessment
• Daily chlorhexidine gluconate bathing for at-risk populations
• Consider decolonization and Active Surveillance Testing
• Gown and glove all ICU patients

Summary

• MRSA bacteremia is a serious, life-threatening HAI
• Often secondary to another infection site
• Prevention requires understanding infection epidemiology

References

• Extensive bibliography of studies and resources on MRSA prevention and control