**2.** *S. aureus* **colonization**

*S. aureus* is a part of the normal human flora; up to 50% of healthy individuals may be persis‐ tently colonized with it. Colonization with *S. aureus* can be persistent in up to 20% of cases, intermittent in 60%, and always absent in up to 20% of people. In a study performed on the general US population that looked at colonization rates in the nares with *S. Aureus*, it was found that the prevalence of MRSA colonization was 0.8% between 2001 and 2002, and went up to 1.5% between 2003 and 2004. The anterior nares is felt to be the major site of *S. aureus* colonization, but some people can be colonized with *S. aureus* outside the nares in areas such as the throat, axilla, inguinal region, and perirectal area. Several conditions may increase the rate of colonization such as diabetes mellitus, HIV infection, underlying skin diseases, and end stage renal disease requiring hemodialysis. Colonization typically precedes *S. aureus* infection. These conditions can place the subject at a higher risk of invasive staphylococcal infections such as bacteremia, which is why much of infection control and prevention efforts target colonization with *S. aureus.*

Nasal carriage of *S. aureus* colonization has been associated with the development of infec‐ tions. A substantial proportion of cases of *S. aureus* bacteremia appear to be of endog‐ enous origin as they originate from colonies in the nasal mucosa. This is one reason why strategies to prevent systemic *S. aureus* infections by eliminating nasal carriage need to be supported.
