What is the mortality rate for Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia?

Mortality Rate for MRSA Bacteremia

The mortality rate for Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is approximately 40-60%, with significant variation based on patient population, comorbidities, and treatment approach.

Overview of MRSA Bacteremia Mortality

MRSA bacteremia represents one of the most serious bloodstream infections with consistently high mortality rates across different settings. The evidence reveals several key patterns:

General Mortality Rates

• In critically ill patients, MRSA bacteremia carries a 30-day mortality rate of 53.2% and in-hospital mortality rate of 63.8% 1
• In a study of MRSA bacteremia in COVID-19 patients, mortality was reported at 61.7% 2
• In community-diagnosed MRSA infections, 21.8% of patients died within one year compared to 5% of non-MRSA patients 3
• In cancer patients with MRSA bacteremia, 60-day mortality was reported at 12%, with 6-month overall mortality at 43.2% 4

Factors Affecting Mortality

Patient-Related Factors

• Age: Advanced age is independently associated with higher mortality 1
• Comorbidities: Presence of conditions like:
  • Acute renal failure
  • Need for mechanical ventilation
  • Immunosuppression
  • Malignancy (36.1% of MRSA bacteremia patients in one study) 5

Infection-Related Factors

• Source of infection: Pneumonia as the source of MRSA bacteremia is associated with higher mortality 5
• Community-onset infection: Associated with higher mortality compared to hospital-acquired infection 4
• Secondary BSI: When bacteremia is secondary to another infection site 4

Treatment-Related Factors

• Antibiotic choice: Vancomycin treatment was associated with poorer outcomes in some studies, particularly when:
  • The source is pneumonia (due to poor tissue penetration) 5
  • The vancomycin MIC is ≥2 g/mL 4
• Early appropriate therapy: Patients treated with vancomycin alone had better response rates (90%) compared to those treated with other antibiotics (47%) 6

Attributable Mortality

A critical concept in understanding MRSA bacteremia mortality is attributable mortality - the excess mortality directly caused by the MRSA infection:

• MRSA bacteremia has an attributable mortality rate of 23.4% (compared to 1.3% for methicillin-susceptible S. aureus bacteremia) 1
• This represents a significant difference of 22.1% in attributable mortality between MRSA and MSSA bacteremia 1

Special Populations

Intensive Care Unit Patients

• Higher mortality rates (53-64%) compared to general hospital populations 1
• Independent predictors of mortality include acute renal failure, prolonged mechanical ventilation, advanced age, and methicillin resistance 1

Cancer Patients

• 60-day mortality: 12%
• 6-month mortality: 43.2% 4
• Risk factors: community-onset infection, secondary BSI, vancomycin MIC≥2 g/mL 4

COVID-19 Patients

• Particularly high mortality rate of 61.7% in patients with COVID-19 and MRSA bacteremia 2
• Most infections were secondary (76.5%) rather than co-infections (16.5%) 2

Implications for Treatment

The high mortality rate of MRSA bacteremia underscores the importance of:

1. Early appropriate antimicrobial therapy: Particularly important in high-risk patients
2. Source control: Identifying and addressing the source of infection (catheter removal, drainage of abscesses)
3. Careful antibiotic selection: Consider alternatives to vancomycin when:
   • The source is pneumonia
   • The vancomycin MIC is elevated
   • There is poor clinical response

The evidence clearly demonstrates that MRSA bacteremia remains a serious infection with substantial mortality risk, requiring prompt diagnosis and appropriate management to improve outcomes.