Staph bacteria are normally found on the skin or in the nose of about one-third of the population. If you have staph on your skin or in your nose but aren't sick, you are said to be "colonized" but not infected with MRSA. Healthy people can be colonized with MRSA and have no ill effects, however, they can pass the germ to others.
Staph bacteria are generally harmless unless they enter the body through a cut or other wound, and even then they often cause only minor skin problems in healthy people. But in older adults and people who are ill or have weakened immune systems, ordinary staph infections can cause serious illness called methicillin-resistant Staphylococcus aureus or MRSA.
In the 1990s, a type of MRSA began showing up in the wider community. Today, that form of staph, known as community-associated MRSA, or CA-MRSA, is responsible for many serious skin and soft tissue infections and for a serious form of pneumonia. When not treated properly, MRSA infection can be fatal." http://www.mayoclinic.com/health/mrsa/DS00735/DSECTION=1
Risk factors for hospital-acquired (HA) MRSA include:
These are the main risk factors for community-acquired (CA) MRSA: