Community-associated methicillin-resistant Staphylococcus aureus prevalence: how common is it? A methodological...

Area of Science:

• Infectious Diseases
• Epidemiology
• Public Health Microbiology

Background:

• Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are a growing public health concern.
• Geographic variations in CA-MRSA prevalence exist, compounded by diverse case-finding methodologies in existing studies.
• Significant variability in reported CA-MRSA prevalence necessitates an investigation into methodological influences.

Purpose of the Study:

• To evaluate how three distinct methods for ascertaining CA-MRSA prevalence yield different estimates.
• To identify key factors contributing to variability in CA-MRSA prevalence data.
• To inform standardized approaches for CA-MRSA surveillance and reporting.

Main Methods:

• Employed three methods for identifying CA-MRSA colonization/infection in New York City.
• Method 1: Retrospective review of clinical and surveillance cultures via hospital database.
• Methods 2 & 3: Prospective surveillance cultures from emergency department and community settings, respectively.

Main Results:

• Prevalence estimates for CA-MRSA varied substantially based on the chosen denominator.
• Using all nares cultures yielded 0.3%-0.6% prevalence.
• Using all S. aureus yielded 1.2%-5% prevalence, while using all MRSA yielded 5.5%-50% prevalence.

Conclusions:

• Methodological variability in case-finding significantly impacts CA-MRSA prevalence estimates.
• Critical factors for comparing CA-MRSA rates include the definition of CA-MRSA, denominator selection, and sample collection methods/settings.
• Standardized methodologies are essential for accurate and comparable CA-MRSA surveillance.