Rapid emergence of methicillin-resistant Staphylococcus aureus (MRSA) among children and adolescents in northern Manitoba, 2003-2006.

The global spread of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) since the mid-1990s is a major public health concern. The epidemiology of CA-MRSA differs from that of health-care-associated MRSA (HCA-MRSA), and this is reflected at the genetic level. Resistance to beta-lactams is encoded in the mecA gene, which is carried, along with resistance determinants for other antibiotics, on the staphylococcal chromosomal cassette (SCC). CA-MRSA typically carries a type IV SCC, which is smaller and encodes resistance to fewer antibiotics than the SCC of HCA-MRSA clones. This may help to explain the ecologic success of CA-MRSA in the community setting and may facilitate horizontal transfer of type IV SCC into other methicillin-sensitive strains.