title: Are community-associated methicillin-resistant Staphylococcus aureus (MRSA) strains replacing traditional nosocomial MRSA strains?
abstract: BACKGROUND
  Recent studies have suggested that community-associated methicillin-resistant Staphylococcus aureus (MRSA) infection is encroaching on health care settings. We describe the epidemiology of hospital-onset community-associated MRSA bloodstream infections using phenotypic and genotypic analysis.
  
  
  METHODS
  Using an update of an established rule derived from antibiotic susceptibilities, we inferred genotypes (i.e., community [CG] or hospital [HG]) for 208 MRSA isolates from hospital-onset (>72 h after hospital admission) bloodstream infections during 2000-2006. We compared demographic characteristics, risk factors, and outcomes of patients infected with CG or HG strains.
  
  
  RESULTS
  Total hospital-onset MRSA bloodstream infection incidence density rates for the periods January 2000-June 2003 and July 2003-December 2006 (0.215 cases per 1000 patient-days and 0.207 cases per 1000 patient-days, respectively) were stable (risk ratio, 1.0; 95% confidence interval, 0.7-1.3; P = .79, period 2 vs. period 1). However, the risk that these bloodstream infections were due to CG strains doubled (risk ratio, 1.9; 95% confidence interval, 1.2-3.1; P = .01), whereas the risk due to HG strains decreased (risk ratio, 0.7; 95% confidence interval, 0.46-0.93; P = .02). After adjustment for comorbidities in multivariate analysis, no significant risk factors for or outcomes of infections due to CG versus HG strains were detected. Patients infected with HG strains showed a trend toward later day of acquisition of a positive blood culture, and those infected with CG strains showed trend toward greater risk of intensive care unit admission.
  
  
  CONCLUSIONS
  Although total hospital-onset MRSA bloodstream infection rates were relatively stable during 2000-2006, CG strains were responsible for an increasing proportion of cases (from 24% to 49%), suggesting replacement of traditional hospital-associated strains. For most risk factors and outcomes, patients infected with CG and HG strains were similar, suggesting that, thus far, CG strains are behaving like their traditional hospital-associated counterparts.
authors.affiliation: Division of Infectious Disease, Department of Medicine, Rush University Medical Center, and Division of Infectious Disease, Department of Medicine, Stroger Hospital of Cook County, Chicago, Illinois 60612, USA. kyle_popovich@rush.edu
authors.forename: Kyle J
authors.initials: KJ
authors.lastname: Popovich
authors.forename: Robert A
authors.initials: RA
authors.lastname: Weinstein
authors.forename: Bala
authors.initials: B
authors.lastname: Hota
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016470:Bacteremia / Q000453:epidemiology / Q000382:microbiology; D017714:Community-Acquired Infections / Q000453:epidemiology* / Q000382:microbiology; D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D015994:Incidence; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D011379:Prognosis; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents