title: A population-based study of the incidence and molecular epidemiology of methicillin-resistant Staphylococcus aureus disease in San Francisco, 2004-2005.
abstract: BACKGROUND
  Methicillin-resistant Staphylococcus aureus (MRSA) infections have become a major public health problem in both the community and hospitals. Few studies have characterized the incidence and clonal composition of disease-causing strains in an entire population. Our objective was to perform a population-based survey of the clinical and molecular epidemiology of MRSA disease in San Francisco, California.
  
  
  METHODS
  We prospectively collected 3985 MRSA isolates and associated clinical and demographic information over a 12-month period (2004-2005) at 9 San Francisco-area medical centers. A random sample of 801 isolates was selected for molecular analysis.
  
  
  RESULTS
  The annual incidence of community-onset MRSA disease among San Francisco residents was 316 cases per 100,000 population, compared with 31 cases per 100,000 population for hospital-onset disease. Persons who were aged 35-44 years, were men, and were black had the highest incidence of community-onset disease. The USA300 MRSA clone accounted for 234 cases of community-onset disease and 15 cases of hospital-onset disease per 100,000 population, constituting an estimated 78.5% and 43.4% of all cases of MRSA disease, respectively. Patients with community-onset USA300 MRSA versus non-USA300 MRSA disease were more likely to be male, be of younger age, and have skin and soft-tissue infections. USA300 strains were generally more susceptible to multiple antibiotics, although decreased susceptibility to tetracycline was observed in both community-onset (P = .008) and hospital-onset (P = .03) USA300 compared to non-USA300 strains.
  
  
  CONCLUSIONS
  The annual incidence of community-onset MRSA disease in San Francisco is substantial, surpassing that of hospital-onset disease. USA300 is the predominant clone in both the community and hospitals. The dissemination of USA300 from the community into the hospital setting has blurred its distinction as a community-associated pathogen.
authors.affiliation: Div. of Infectious Diseases, University of California, San Francisco, 513 Parnassus Ave., S-380, Box 0654, San Francisco, CA 94143, USA. catherine.liu@ucsf.edu
authors.forename: Catherine
authors.initials: C
authors.lastname: Liu
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Graber
authors.forename: Michael
authors.initials: M
authors.lastname: Karr
authors.forename: Binh An
authors.initials: BA
authors.lastname: Diep
authors.forename: Li
authors.initials: L
authors.lastname: Basuino
authors.forename: Brian S
authors.initials: BS
authors.lastname: Schwartz
authors.forename: Mark C
authors.initials: MC
authors.lastname: Enright
authors.forename: Simon J
authors.initials: SJ
authors.lastname: O'Hanlon
authors.forename: Jonathon C
authors.initials: JC
authors.lastname: Thomas
authors.forename: Francoise
authors.initials: F
authors.lastname: Perdreau-Remington
authors.forename: Shelley
authors.initials: S
authors.lastname: Gordon
authors.forename: Helen
authors.initials: H
authors.lastname: Gunthorpe
authors.forename: Richard
authors.initials: R
authors.lastname: Jacobs
authors.forename: Peter
authors.initials: P
authors.lastname: Jensen
authors.forename: Gifford
authors.initials: G
authors.lastname: Leoung
authors.forename: James S
authors.initials: JS
authors.lastname: Rumack
authors.forename: Henry F
authors.initials: HF
authors.lastname: Chambers
mesh_terms: D000328:Adult; D017714:Community-Acquired Infections / Q000453:epidemiology* / Q000382:microbiology; D005260:Female; D006801:Humans; D008297:Male; D016106:Methicillin Resistance; D017720:Molecular Epidemiology; D011159:Population Surveillance; D011446:Prospective Studies; D012495:San Francisco / Q000453:epidemiology; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology* / Q000635:transmission; D013207:Staphylococcal Skin Infections / Q000453:epidemiology / Q000382:microbiology / Q000503:physiopathology; D013211:Staphylococcus aureus