Community-associated methicillin-resistant Staphylococcus aureus: It's not just in communities anymore

Methicillin-resistant Staphylococcus aureus (MRSA) infections continue to spread worldwide. From an epidemiologic perspective, the risk factors for infections caused by health care-associated strains of methicillin-resistant S. aureus (HA-MRSA) include hospitalization within the last year; having had surgery, received dialysis, or resided in a long-term care facility in the previous year; having a permanent indwelling catheter or percutaneous medical device; or having previously had an MRSA infection. Strains causing infections in patients without risk factors for MRSA are called community-associated MRSA (CA-MRSA). The laboratory definition of CA-MRSA is more of a moving target. While CA-MRSA strands typically are resistant only to oxacillin and macrolides, carry SCCmec type IV, and harbor the genes encoding the Panton-Valentine leukocidin toxin, there are at least four distinct lineages defined by pulsed-field gel electrophoresis that fit this definition. CA-MRSA strains are already moving into a variety of health care institutions and causing infections. Thus, the line between HA- and CA-MRSA is blurring.