title: A Simulation Study to Assess Indicators of Antimicrobial Use as Predictors of Resistance: Does It Matter Which Indicator Is Used?
abstract: OBJECTIVE
  Indicators of antimicrobial use have been described previously, but few studies have compared their accuracy in prediction of antimicrobial resistance in hospital settings. This study aimed to identify conditions under which significant differences would be observed in the predictive accuracy of indicators in the context of surveillance of intensive care units (ICUs).
  
  
  METHODS
  Ten resistance / antimicrobial use combinations were studied. We used simulation to determine if Québec's network of 81 ICUs or the National Healthcare Safety Network (NHSN) of 2952 ICUs are large enough to allow the detection of predetermined differences between the most accurate and 1) the second most accurate indicator, and 2) the least accurate indicator, in more than 80% of simulations. For each indicator, we simulated absolute errors in prediction for each ICU and each 4-week period, for surveillance lasting up to 5 years. Absolute errors were generated following a binomial distribution, using mean absolute errors (MAEs) observed in 9 ICUs as the average proportion; simulated MAEs were compared using t-tests. This was repeated 1000 times per scenario.
  
  
  RESULTS
  When comparing the two most accurate indicators, 80% power was reached less often with the Québec network versus the NHSN (0/20 versus 2/20 scenarios, with 5 years of surveillance data), a finding reinforced when comparing the most and least accurate indicators (3/20 versus 20/20 scenarios). When simulating 1 year of data, scenarios reaching an 80% power dropped to 0/20, comparing the two most accurate indicators with the larger network, and to 1/20, comparing the most and least accurate indicators with the smaller network.
  
  
  CONCLUSIONS
  Most of the time (72%), identifying an indicator of antimicrobial use predicting antimicrobial resistance with a better accuracy was not possible. The choice of an indicator for an eventual surveillance system should rely on criteria other that predictive accuracy.
authors.affiliation: Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec, Canada.|Direction des risques biologiques et de la santé au travail, Institut national de santé publique du Québec, Québec and Montréal, Québec, Canada.
authors.forename: Elise
authors.initials: E
authors.lastname: Fortin
authors.affiliation: Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec, Canada.|Direction des risques biologiques et de la santé au travail, Institut national de santé publique du Québec, Québec and Montréal, Québec, Canada.|Department of Pediatrics, The Montréal Children's Hospital, McGill University, Montréal, Québec, Canada.
authors.forename: Caroline
authors.initials: C
authors.lastname: Quach
authors.affiliation: Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec, Canada.|Department of Pediatrics, The Montréal Children's Hospital, McGill University, Montréal, Québec, Canada.
authors.forename: Patricia S
authors.initials: PS
authors.lastname: Fontela
authors.affiliation: Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec, Canada.
authors.forename: David L
authors.initials: DL
authors.lastname: Buckeridge
authors.affiliation: Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec, Canada.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Platt
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001424:Bacterial Infections / Q000175:diagnosis* / Q000188:drug therapy / Q000453:epidemiology; D003198:Computer Simulation; D003428:Cross Infection / Q000175:diagnosis* / Q000188:drug therapy / Q000453:epidemiology; D024881:Drug Resistance, Bacterial; D006761:Hospitals; D006801:Humans; D007362:Intensive Care Units; D011159:Population Surveillance
chemical_list: D000900:Anti-Bacterial Agents