title: Impact of hospital length of stay on the distribution of Gram negative bacteria and likelihood of isolating a resistant organism in a Canadian burn center.
abstract: BACKGROUND
  The impact of hospital length of stay (LOS) on the distribution and susceptibility of Gram negative bacteria (GNB) causing infection in burn patients remains unexplored. Knowledge of causative pathogens is important in guiding empiric antibiotic therapy.
  
  
  OBJECTIVE
  To characterize the distribution of GNB causing infection and to identify changes in susceptibility with LOS in a tertiary care burn center.
  
  
  METHODS
  A retrospective review of all admissions to the Ross Tilley Burn Centre at Sunnybrook Health Sciences Centre with clinical cultures yielding GNB (duplicates excluded) between March 12, 2010 to July 17, 2013 was completed. Positive cultures were categorized into 5 clinically relevant time periods (in days) based on specimen collection date relative to the patient's date of admission: 0-7, 7-14, 14-21, 21-28, >28. Chi-square for proportions was used to compare the time periods.
  
  
  RESULTS
  The proportion of patients with clinical cultures for P. aeruginosa increased with hospital LOS (0-7 days: 8% vs. >28 days: 55%; p<0.05). Conversely, clinical cultures for H. influenzae occurred primarily within the first 7 days of hospitalization (0-7 days: 36% vs. >28 days: 0.7%; p<0.05). Enterobacteriaceae isolation was highest between 7 and 14 days of hospitalization (7-14 days: 62% vs. >28 days: 38%; p<0.05). Antibiotic resistance was directly proportional to hospital LOS (% patients with multidrug resistant GNB increased from 6% [LOS 0-7 days] to 44% [LOS>28 days]; p<0.05).
  
  
  CONCLUSIONS
  This study provides objective data documenting changes in species and resistance patterns of GNB causing infection in patients admitted to a burn center as a function of hospital LOS; which may support delaying the use of broad spectrum antibiotics (e.g. carbapenems and beta-lactam/beta-lactamase inhibitors) in clinically stable patients.
authors.affiliation: University of Toronto, Leslie L. Dan Faculty of Pharmacy, Toronto, Ontario, Canada.
authors.forename: Marsail
authors.initials: M
authors.lastname: Wanis
authors.affiliation: University of Toronto, Leslie L. Dan Faculty of Pharmacy, Toronto, Ontario, Canada; Sunnybrook Health Sciences Centre, Department of Pharmacy, Toronto, Ontario, Canada; Sunnybrook Health Sciences Centre, Department of Microbiology and Division of Infectious Diseases, Toronto, Ontario, Canada; Sunnybrook Research Institute, Toronto, Ontario, Canada. Electronic address: sandra.walker@sunnybrook.ca.
authors.forename: Sandra A N
authors.initials: SAN
authors.lastname: Walker
authors.affiliation: Sunnybrook Health Sciences Centre, Department of Microbiology and Division of Infectious Diseases, Toronto, Ontario, Canada; Sunnybrook Research Institute, Toronto, Ontario, Canada; University of Toronto, Faculty of Medicine, Toronto, Ontario, Canada.
authors.forename: Nick
authors.initials: N
authors.lastname: Daneman
authors.affiliation: Sunnybrook Health Sciences Centre, Department of Pharmacy, Toronto, Ontario, Canada.
authors.forename: Marion
authors.initials: M
authors.lastname: Elligsen
authors.affiliation: Sunnybrook Health Sciences Centre, Department of Pharmacy, Toronto, Ontario, Canada.
authors.forename: Lesley
authors.initials: L
authors.lastname: Palmay
authors.affiliation: Sunnybrook Health Sciences Centre, Department of Microbiology and Division of Infectious Diseases, Toronto, Ontario, Canada; Sunnybrook Research Institute, Toronto, Ontario, Canada; University of Toronto, Faculty of Medicine, Toronto, Ontario, Canada.
authors.forename: Andrew
authors.initials: A
authors.lastname: Simor
authors.affiliation: Sunnybrook Health Sciences Centre, Ross Tilley Burn Centre, Toronto, Ontario, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: Cartotto
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D002053:Burn Units; D002056:Burns / Q000453:epidemiology* / Q000382:microbiology; D002170:Canada / Q000453:epidemiology; D015331:Cohort Studies; D024881:Drug Resistance, Bacterial; D004755:Enterobacteriaceae / Q000302:isolation & purification / Q000502:physiology; D004756:Enterobacteriaceae Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D005260:Female; D006090:Gram-Negative Bacteria / Q000302:isolation & purification* / Q000502:physiology; D016905:Gram-Negative Bacterial Infections / Q000188:drug therapy / Q000453:epidemiology* / Q000382:microbiology; D006192:Haemophilus Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D006193:Haemophilus influenzae / Q000302:isolation & purification / Q000502:physiology; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011552:Pseudomonas Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000302:isolation & purification / Q000502:physiology; D012189:Retrospective Studies; D012307:Risk Factors; D014946:Wound Infection / Q000188:drug therapy / Q000453:epidemiology* / Q000382:microbiology; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents
keywords: Burn; Distribution; Gram negative bacteria; Length of stay; Prevalence; Resistance