Before the middle 90′s, infections that could be attributed to MRSA were uncommon. The only cases of MRSA were found mostly with those who already had previous instances of injection drug use, or some forms of anti-microbial therapy. Usually those who are infected with MRSA tend to be those who do not practice good hygiene or have undergone some action or occurrence that caused the person to be exposed to it.

It is suggested that CA-MRSA is a genetically unique strain, unlike the strains that are usually diagnosed. MRSA has different forms allowing it to be contracted in multiple ways. The uniqueness of the MRSA strain allows it to cause different symptoms of illness, and a different variation of severity unlike strains of Staph that are not Methicillin resistant. S. Aureus, the MRSA strain, can cause very serious invasive infections. These could include septic phlebitis, influenza, pneumonia, toxic shock syndrome, and even Waterhouse Friderichsen syndrome, which can cause severe bacterial infection as well as hemorrhaging of the adrenal glands.

More information on the official guidelines can be found here:
Official Guidelines for MRSA Staph.