S. aureus is an important cause of community-acquired infections and a leading cause of nosocomial infections.

• S. aureus is a component of the normal human flora, most frequently colonizing the anterior nares and oropharynx but also colonizing the skin (particularly damaged skin), vagina, axilla, and perineum. These sites of colonization are reservoirs for future infection.
• Of healthy persons, ~30% are transiently colonized with S. aureus, while ~10% are persistently colonized. The rate is elevated among insulin-dependent diabetic pts, HIV-infected persons, injection drug users, hemodialysis pts, and pts with skin damage.
• Transmission of S. aureus most frequently results from direct personal contact, although spread via respiratory secretions has been reported. Most S. aureus infections are caused by a strain that is already a component of the pt's own microbiota.
• Methicillin-resistant S. aureus (MRSA) is common in hospitals, and its prevalence is increasing dramatically in community settings among individuals without prior medical exposure.
  • - In the United States, strain USA300 (defined by pulsed-field gel electrophoresis) causes most community-acquired MRSA (CA-MRSA) infections and can cause severe disease in immunocompetent pts.