Staphylococcal infections are those caused by staphylococci, which are common gram-positive bacteria. Normally found in the nose and on the skin of 20 to 30 percent of healthy adults (and less commonly in the mouth, mammary glands, and genitourinary, intestinal, and upper respiratory tracts), staphylococci do no harm most of the time. However, a break in the skin or another injury may allow the bacteria to penetrate the body's defenses and cause infection.
Although staph bacteria are carried in the nose, it is not typically an airborne pathogen. It is also not found in dirt or mud. Most infections occur through direct physical contact of the staphylococci with a break in the skin (cut or scrape). Inanimate objects such as clothing, bed linens, or furniture may also be a source of infection when they become soiled with wound drainage and a non-infected person then is exposed to the drainage. If there is no break in the skin, contact with infected persons or articles may result in infection.