title: Utility of prior screening for methicillin-resistant Staphylococcus aureus in predicting resistance of S. aureus infections.
abstract: BACKGROUND
  Screening for methicillin-resistant Staphylococcus aureus (MRSA) is intended to reduce nosocomial spread by identifying patients colonized by MRSA. Given the widespread use of this screening, we evaluated its potential clinical utility in predicting the resistance of clinical isolates of S. aureus.
  
  
  METHODS
  We conducted a 2-year retrospective cohort study that included patients with documented clinical infection with S. aureus and prior screening for MRSA. We determined test characteristics, including sensitivity and specificity, of screening for predicting the resistance of subsequent S. aureus isolates.
  
  
  RESULTS
  Of 510 patients included in the study, 53 (10%) had positive results from MRSA screening, and 79 (15%) of infecting isolates were resistant to methicillin. Screening for MRSA predicted methicillin resistance of the infecting isolate with 99% (95% confidence interval [CI] 98%-100%) specificity and 63% (95% CI 52%-74%) sensitivity. When screening swabs were obtained within 48 hours before isolate collection, sensitivity increased to 91% (95% CI 71%-99%) and specificity was 100% (95% CI 97%-100%), yielding a negative likelihood ratio of 0.09 (95% CI 0.01-0.3) and a negative predictive value of 98% (95% CI 95%-100%). The time between swab and isolate collection was a significant predictor of concordance of methicillin resistance in swabs and isolates (odds ratio 6.6, 95% CI 1.6-28.2).
  
  
  CONCLUSIONS
  A positive result from MRSA screening predicted methicillin resistance in a culture-positive clinical infection with S. aureus. Negative results on MRSA screening were most useful for excluding methicillin resistance of a subsequent infection with S. aureus when the screening swab was obtained within 48 hours before collection of the clinical isolate.
authors.forename: Derek R
authors.initials: DR
authors.lastname: MacFadden
authors.forename: Marion
authors.initials: M
authors.lastname: Elligsen
authors.forename: Ari
authors.initials: A
authors.lastname: Robicsek
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Ricciuto
authors.forename: Nick
authors.initials: N
authors.lastname: Daneman
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D016106:Methicillin Resistance; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects; D008826:Microbial Sensitivity Tests / Q000706:statistics & numerical data; D008875:Middle Aged; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000175:diagnosis / Q000188:drug therapy* / Q000382:microbiology
references.citation: Scand J Infect Dis. 2011 Jul;43(6-7):456-62
references.pmid: 21366406
references.citation: Infect Control Hosp Epidemiol. 2010 Jun;31(6):584-91
references.pmid: 20426656
references.citation: Infect Control Hosp Epidemiol. 2012 Nov;33(11):1113-7
references.pmid: 23041809
references.citation: Am J Emerg Med. 2007 Jul;25(6):597-607
references.pmid: 17606081
references.citation: J Antimicrob Chemother. 2010 Dec;65(12):2658-65
references.pmid: 20947620
references.citation: Emerg Infect Dis. 2002 Jul;8(7):702-7
references.pmid: 12095438
references.citation: Antimicrob Agents Chemother. 2005 Feb;49(2):760-6
references.pmid: 15673761
references.citation: J Hosp Infect. 1997 Jan;35(1):9-16
references.pmid: 9032631
references.citation: Clin Infect Dis. 2004 Sep 15;39(6):776-82
references.pmid: 15472807
references.citation: BMC Infect Dis. 2011 Oct 19;11:279
references.pmid: 22011388
references.citation: J Antimicrob Chemother. 2011 May;66 Suppl 4:iv43-iv48
references.pmid: 21521706
references.citation: PLoS Med. 2011 Oct;8(10):e1001104
references.pmid: 22022233
references.citation: J Clin Microbiol. 2008 Feb;46(2):588-92
references.pmid: 18057132
references.citation: Infect Control Hosp Epidemiol. 2003 Jun;24(6):415-21
references.pmid: 12828317
references.citation: N Engl J Med. 2011 Apr 14;364(15):1419-30
references.pmid: 21488764
references.citation: Emerg Infect Dis. 2007 Dec;13(12):1840-6
references.pmid: 18258033
references.citation: Arch Intern Med. 2000 Apr 10;160(7):1001-4
references.pmid: 10761966
references.citation: Antimicrob Agents Chemother. 2010 Aug;54(8):3143-8
references.pmid: 20479207
references.citation: Can J Hosp Pharm. 2012 Jan;65(1):31-6
references.pmid: 22479110
references.citation: Clin Infect Dis. 2004 Aug 1;39(3):309-17
references.pmid: 15306996
references.citation: J Hosp Infect. 2006 Mar;62(3):386-8
references.pmid: 16337030
references.citation: N Engl J Med. 2001 Jan 4;344(1):11-6
references.pmid: 11136954
references.citation: J Clin Microbiol. 2005 Jul;43(7):3491-3
references.pmid: 16000487
references.citation: Clin Infect Dis. 1997 Jun;24(6):1052-9
references.pmid: 9195057
references.citation: Ann Intern Med. 2008 Mar 18;148(6):409-18
references.pmid: 18347349