title: Decreasing incidence of Staphylococcus aureus bacteremia over 9 years: greatest decline in community-associated methicillin-susceptible and hospital-acquired methicillin-resistant isolates.
abstract: BACKGROUND
  The impact of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) emergence on the epidemiology of S aureus bacteremia (SAB) is not well documented.
  
  
  METHODS
  This was an observational study of adult (aged ≥18 years) inpatients with SAB in a single 808-bed teaching hospital during 2002-2003, 2005-2006, 2008-2009, and 2010 with period-stratified SAB rate, onset mode, patient characteristics, and outcome.
  
  
  RESULTS
  We encountered a total of 1,098 cases over the entire study period. The rate decreased steadily over time (from 6.64/10(3) discharges in 2002-2003 to 6.49/10(3) in 2005-2006, 5.24/10(3) in 2008-2009, and 5.00/10(3) in 2010; P = .0001), with a greater decline in community-associated cases (0.99/10(3), 0.77/10(3), 0.58/10(3), and 0.40/10(3), respectively; P = .0005) compared with health care-associated cases (5.65/10(3), 5.72/10(3), 4.66/10(3), and 4.60/10(3), respectively; P = .005). The decline was principally in MSSA (3.11/10(3), 2.21/10(3), 2.24/10(3), and 1.75/10(3), respectively; P = .00006), including both community-associated (P = .0002) and health care-associated cases (P = .006). Although overall rate changes in MRSA were not significant (P = .09), hospital-onset MRSA decreased markedly (P < .00001), whereas CA-MRSA increased (P = .03). The all-cause 100-day mortality rate did not change significantly (25.6% for 2002-2003, 25.2% for 2005-2006, 28.1% for 2008-2009, and 32.2% for 2010; P = .10). Differences in MSSA/MRSA-associated mortality decreased (20.1% vs 30.6%, P = .03 for 2002-2003; 18.1% vs 28.9%, P = .05 for 2005-2006; 21.7% vs 32.9%, P = .05 for 2008-2009; and 29.3% vs 34.9, P = .5 for 2010).
  
  
  CONCLUSIONS
  SAB incidence is decreasing, with the greatest decline in community-associated MSSA and hospital-onset MRSA cases. Most health care-associated cases currently are community-onset. MRSA/MSSA-related mortality is comparable. These changes are likely related to the emergence of CA-MRSA and the inpatient-to-outpatient shift in health care.
authors.affiliation: Department of Medicine, St John Hospital and Medical Center, Grosse Pointe Woods, MI 48236, USA. riad.khatib@stjohn.org
authors.forename: Riad
authors.initials: R
authors.lastname: Khatib
authors.forename: Mamta
authors.initials: M
authors.lastname: Sharma
authors.forename: Sugantha
authors.initials: S
authors.lastname: Iyer
authors.forename: Mohamad G
authors.initials: MG
authors.lastname: Fakih
authors.forename: Karam M
authors.initials: KM
authors.lastname: Obeid
authors.forename: Anilrudh
authors.initials: A
authors.lastname: Venugopal
authors.forename: Joel
authors.initials: J
authors.lastname: Fishbain
authors.forename: Leonard B
authors.initials: LB
authors.lastname: Johnson
authors.forename: Madhuri
authors.initials: M
authors.lastname: Segireddy
authors.forename: Jinson
authors.initials: J
authors.lastname: Jose
authors.forename: Kathleen
authors.initials: K
authors.lastname: Riederer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016470:Bacteremia / Q000453:epidemiology* / Q000382:microbiology; D017714:Community-Acquired Infections / Q000453:epidemiology* / Q000382:microbiology; D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology; D005260:Female; D006784:Hospitals, Teaching; D006801:Humans; D015994:Incidence; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D008875:Middle Aged; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D055815:Young Adult