Fifteen-Year Study of the Changing Epidemiology of Methicillin-Resistant Staphylococcus aureus

Nancy F. Crum*, Rachel U. Lee, Scott A. Thornton, O. Colin Stine, Mark R. Wallace, Chris Barrozo, Ananda Keefer-Norris, Sharon Judd, Kevin L. Russell

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

167 Scopus citations


Purpose: The study's purpose was to elucidate the evolutionary, microbiologic, and clinical characteristics of methicillin-resistant Staphylococcus aureus (MRSA) infections. Methods: MRSA cases from military medical facilities in San Diego, from 1990 to 2004, were evaluated and categorized as community-acquired or nosocomial. Sequence type, staphylococcal chromosomal cassette gene type, and Panton-Valentine leukocidin gene status were determined for a subset of isolates. Results: Over the 15-year period, 1888 cases of MRSA were identified; 65% were community acquired. The incidence (155 infections/100 000 person-year in 2004) and household-associated cases rapidly increased since 2002. Among persons with community-acquired MRSA, 16% were hospitalized and only 17% were initially given an effective antibiotic. Community-acquired MRSA cases compared with nosocomial MRSA cases were more often soft-tissue and less often urinary, lung, or bloodstream infections (P < .001). Patients with community-acquired MRSA were younger (22 vs 64 years, P < .001) and less likely to have concurrent medical conditions (9% vs 98%, P < .001). Clindamycin resistance increased among community-acquired MRSA isolates during 2003 and 2004 compared with previous years (79% vs 13%, P < .001). Genetically, nosocomial MRSA isolates were significantly different than those acquired in the community. Although community-acquired MRSA isolates were initially diverse by 2004, one strain (staphylococcal chromosomal cassette type IV, sequence type 8, Panton-Valentine leukocidin gene positive) became the predominant isolate. Conclusions: Community-acquired and intrafamilial MRSA infections have increased rapidly since 2002. Our 15 years of surveillance revealed the emergence of distinct community-acquired MRSA strains that were genetically unrelated to nosocomial MRSA isolates from the same community.

Original languageEnglish
Pages (from-to)943-951
Number of pages9
JournalThe American Journal of Medicine
Issue number11
StatePublished - Nov 2006
Externally publishedYes


  • Community-acquired
  • Epidemiology
  • MRSA
  • Methicillin-resistant Staphylococcus aureus


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