title: Hospital- and patient-related factors associated with differences in hospital antibiotic use: analysis of national surveillance results.
abstract: BACKGROUND
  Surveillance data of antibiotic use are increasingly being used for benchmarking purposes, but there is a lack of studies dealing with how hospital- and patient-related factors affect antibiotic utilization in hospitals. Our objective was to identify factors that may contribute to differences in antibiotic use.
  
  
  METHODS
  Based on pharmacy sales data (2006-2011), use of all antibiotics, all penicillins, and broad-spectrum antibiotics was analysed in 22 Health Enterprises (HEs). Antibiotic utilization was measured in World Health Organisation defined daily doses (DDDs) and hospital-adjusted (ha)DDDs, each related to the number of bed days (BDs) and the number of discharges. For each HE, all clinical specialties were included and the aggregated data at the HE level constituted the basis for the analyses. Fourteen variables potentially associated with the observed antibiotic use - extracted from validated national databases - were examined in 12 multiple linear regression models, with four different measurement units: DDD/100 BDs, DDD/100 discharges, haDDD/100 BDs and haDDD/100 discharges.
  
  
  RESULTS
  Six variables were independently associated with antibiotic use, but with a variable pattern depending on the regression model. High levels of nurse staffing, high proportions of short (<2 days) and long (>10 days) hospital stays, infectious diseases being the main ICD-10 diagnostic codes, and surgical diagnosis-related groups were correlated with a high use of all antibiotics. University affiliated HEs had a lower level of antibiotic utilization than other institutions in eight of the 12 models, and carried a high explanatory strength. The use of broad-spectrum antibiotics correlated strongly with short and long hospital stays. There was a residual variance (30%-50% for all antibiotics; 60%-70% for broad-spectrum antibiotics) that our analysis did not explain.
  
  
  CONCLUSIONS
  The factors associated with hospital antibiotic use were mostly non-modifiable. By adjusting for these factors, it will be easier to evaluate and understand observed differences in antibiotic use between hospitals. Consequently, the inter-hospital differences can be more confidently acted upon. The residual variation is presumed to largely reflect prescriber-related factors.
authors.affiliation: Department of Infectious Diseases, Oslo University Hospital Trust, Oslo, Norway.
authors.forename: Jon Birger
authors.initials: JB
authors.lastname: Haug
authors.affiliation: Department of Infectious Diseases, Oslo University Hospital Trust, Oslo, Norway.
authors.forename: Dag
authors.initials: D
authors.lastname: Berild
authors.affiliation: Microbiology Section, Laboratory Centre, Vestre Viken Hospital Trust, Drammen, Norway.
authors.forename: Mette
authors.initials: M
authors.lastname: Walberg
authors.affiliation: Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway ; Department of Pharmacology, Oslo University Hospital Trust, Oslo, Norway.
authors.forename: Åsmund
authors.initials: Å
authors.lastname: Reikvam
keywords: Antibiotic surveillance; Antibiotic use; Hospitals; Risk factors