Community-associated meticillin-resistant Staphylococcus aureus: the case for a genotypic definition

Area of Science:

• Microbiology
• Infectious Diseases
• Epidemiology

Background:

• Emergence of distinct community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) strains causing infections in healthy individuals.
• Challenges in defining and differentiating CA-MRSA from healthcare-associated (HA)-MRSA due to evolving transmission patterns.
• Need for clear identification for clinical management, epidemiology, and infection control.

Purpose of the Study:

• To review existing definitions of CA-MRSA.
• To propose a new, genetically-based definition for CA-MRSA.

Main Methods:

• Non-systematic review of literature on CA-MRSA definitions and characteristics.

Main Results:

• Epidemiological definitions, once useful, are now inadequate as CA-MRSA strains are increasingly found in healthcare settings.
• CA-MRSA are defined by the acquisition of the mecA gene and are genetically distinct from HA-MRSA.
• Genetic typing (multi-locus sequence or spa typing) combined with staphylococcal cassette chromosome mec analysis is recommended for definition.
• Panton-Valentine leukocidin carriage and antimicrobial susceptibility are indicators, not defining features.

Conclusions:

• MRSA infections require comprehensive characterization including strain type (HA- or CA-MRSA), acquisition setting, and onset location.
• A precise, genetically-based definition is crucial for understanding CA-MRSA epidemiology and implementing effective control strategies.