ABSTRACT. Objective. This study was performed to understand the epidemiology of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections in southern New England children.Methods. A retrospective review was conducted of the medical records of children 0 to 18 years old with MRSA isolated by the Rhode Island Hospital microbiology laboratory (Providence, RI) between 1997 and 2001. A case was classified as either health care-associated MRSA (HCA-MRSA) or CA-MRSA based on time of culture and other strict criteria. The spectrum of illness of the HCA-MRSA and CA-MRSA cases was compared, as were the antibiotic-susceptibility patterns of their isolates. Risk factors for CA-MRSA acquisition were identified, and molecular subtyping of selected isolates was performed.Results. 6,7 In the early 1980s, the first reports of communityacquired (CA)-MRSA in adults emerged. 8 -10 These isolates were found initially in intravenous drug users or members of other high-risk groups with frequent contact with the health care system. In the late 1980s, the first cases of CA-MRSA in children were reported. 11 Most of these children also had a history of frequent health care contact. Thus, although the infections occurred in a community setting, these MRSA strains are better described as health careassociated (HCA) rather than truly CA.From the 1990s to the present, CA-MRSA has emerged as a pathogen in adults and children without traditional risk factors for MRSA acquisition. [12][13][14][15][16] More-recent reports have suggested that other risk factors also may exist, such as household contacts with risk factors for MRSA and child-care attendance. [17][18][19] Notably, the CA-MRSA isolates described in the past decade differ significantly from previous strains of MRSA in that they have distinct DNA-fingerprinting patterns 20 and lack multidrug resistance. 21 Recent research has demonstrated that these strains have novel resistance and virulence genes. Resistance to ␤-lactam antibiotics is conveyed by acquisition of a chromosomal mecA gene that encodes for a penicillin-binding protein with a low affinity for this antibiotic class. The mecA genes are found on mobile genetic elements called staphylococcal chromosomal cassettes (SCCmec). CA-MRSA strains have been found to have a novel allelic form of SCCmec type IV, thus differing from HCA-MRSA strains that carry types I, II, or III SCCmec cassettes. The mecA gene of HCA-MRSA strains is flanked by insertion sequencelike elements, acquired through horizontal gene transfer, which act as a trap for additional unrelated antibiotic-resistance genetic determinants leading to by guest on May 9, 2018 http://pediatrics.aappublications.org/ Downloaded from the multidrug resistance seen in these strains. The smaller type IV SCCmec cassette found in CA-MRSA does not carry any such multiresistance genes 22,23 ; however, these strains can still cause fatal disease. 24 Additionally, CA-MRSA strains, unlike HCA-MRSA strains, have been found to carry virulence genes encoding a leu...