Staphylococcus Aureus--better known as "Staph"--are bacteria commonly found in the noses and on the skin of healthy people. Staph with resistance to the antibiotic methicillin (and other related antibiotics) are known as Methicillin Resistant Staphylococcus Aureus--or MRSA. Resistance means that a particular antibiotic will not work against these bacteria.
When staph are present on or in the body without causing illness, it is called "colonization." At any given time, from 20% to 50% of the general population is colonized with staph bacteria; some may be MRSA, while others are not antibiotic-resistant.
Most people with staph are colonized only. These bacteria can occasionally get through the skin barrier and cause superficial infections (most such infections are not severe). Symptoms of infection vary depending on the part of the body that is infected. Skin infections (the most common site of staph infections) typically result in impetigo and wound infections. Rarely, the bacteria get into the bloodstream and other body sites and can cause more severe illness.
Staph bacteria are spread by contact with the hands, wound drainage, or nasal secretions of a person who is infected or colonized. Persons who have draining wounds are shedding more bacteria and are more infectious than persons who are colonized only. The role of environmental surfaces is less clear but is probably less important than direct person-to-person spread.
Hand washing is the most effective method of preventing the spread of staph. Persons should wash their hands thoroughly with soap and warm running water for at least 15 seconds (or use an alcohol-based sanitizer if water is not available).
Symptoms of a skin infection include purulent drainage (pus); tenderness, redness or swelling; area is warm to the touch or a fever is present. If you are experiencing any of these symptoms with a skin infection, please consult your doctor; take all antibiotics prescribed by your doctor, even after the infection seems to have healed; and keep the wound covered at all times until completely healed.
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