Staphylococcus aureus (S. aureus) is a common type of bacteria that often lives on the surface of the skin of healthy people without causing infection. Sometimes these bacteria penetrate the skin and cause infection of the skin or the tissues underneath (called skin and soft-tissue infections). As a result of overusing antibiotics, certain strains of S. aureus have developed resistance to important antibiotics, such as methicillin, that have been used to treat these types of infections. In the past, doctors have found antibiotic-resistant or methicillin-resistant S. aureus (MRSA) mostly in patients who became infected while they were in a hospital or another health care facility, as opposed to methicillin-sensitive S. aureus (MSSA), which was mostly found in infections that had started outside the hospital setting. Treatment of MRSA requires special types of antibiotics, some of which must be given through veins when initially treating serious or life-threatening infections. Recently, doctors have been finding MRSA with increasing frequency outside the hospital in the general community (community-acquired MRSA). Initially this seemed to occur most often in particular groups of people, such as inmates of correctional facilities, homosexual men, and members of sports teams. Doctors need to know how the pattern of infection with MRSA is changing because treatment practices may need to be changed.