What is the difference between HA-MRSA and CA-MRSA?

In the past, most cases of MRSA were hospital acquired but, in recent years, a distinct subtype of MRSA has emerged in the community setting. The two MRSA types are known as hospital acquired and community acquired (HA and CA-MRSA). HA-MRSA tends to cause invasive and disseminated infections in hospitalized patients, hemodialysis patients, long-term care facility patients, and patients with implanted medical devices. These strains tend to exhibit resistance to a greater number of antibiotic classes than CA-MRSA. CA-MRSA causes the same spectrum of skin infections as methicillin-sensitive (MSSA) S. aureus, most commonly furuncules, boils, and abscesses; however, severe, invasive infections with CA-MRSA have been reported. Additionally, CA-MRSA tends to display a narrower spectrum of antibiotic resistance than HA-MRSA. Trimethoprim-sulfamethoxazole, tetracycline, and clindamycin are antibiotics that will often cover CA-MRSA, although inducible clindamycin resistance is fairly common in CA-MRSA isolates. Therapy is dependent on the severity of infection and the strain susceptibility, with empiric antibiotic coverage determined by prevalence of CA-MRSA in a given community. More serious and hospital-acquired cases are usually treated with vancomycin or linezolid.

Elston DM: Status update: hospital-acquired and community-acquired methicillin-resistant Staphylococcus aureus, Cutis 79(Suppl 6):37–42, 2007.