title: Genodiversity of resistant Pseudomonas aeruginosa isolates in relation to antimicrobial usage density and resistance rates in intensive care units.
abstract: OBJECTIVE
  To evaluate the assumption that resistance rates in intensive care units (ICUs) are markedly influenced by cross-transmission events in addition to high rates of antimicrobial usage.
  
  
  METHODS
  This was a prospective ICU- and laboratory-based surveillance study involving 35 German ICUs from 1999 through 2004. A total of 585 ciprofloxacin- or imipenem-resistant isolates of Pseudomonas aeruginosa were investigated together with resistance rate and unit-based antimicrobial usage density. Antimicrobial use was reported in terms of defined daily doses per 1,000 patient-days. All the strains were assigned to ICU-based genotypes. Genodiversity was calculated as the numbers of indistinguishable ICU-based genotypes found per isolates tested. Reduced ICU-based genodiversity was taken as an indirect measure of frequently occurring cross-transmission events.
  
  
  RESULTS
  The genodiversity of ciprofloxacin- and imipenem-resistant P. aeruginosa isolates was significantly lower (P <=, by Fisher exact test) in ICUs with high resistance rate and low antimicrobial usage density (genodiversity, 0.50 and 0.50, respectively) than in ICUs that featured low resistance rate in the presence of high antimicrobial usage density (genodiversity, 0.90 and 0.95, respectively). In ICUs with low genodiversity, there was a greater rise in resistance rate with increasing antimicrobial usage density, compared with that in ICUs with high diversity.
  
  
  CONCLUSIONS
  This study on resistant P. aeruginosa isolates supports the assumption that high resistance rate in the presence of low antimicrobial usage density results from more-frequent cross-transmission events. A greater rise in resistance rate with increasing antimicrobial usage density in ICUs with low genodiversity indicates that resistance rate in ICUs might be markedly determined by cross-transmission events other than antimicrobial usage.
authors.affiliation: Department of Environmental Health Sciences, University Medical Center Freiburg, Freiburg, Germany. daniel.jonas@uniklinik-freiburg.de
authors.forename: Daniel
authors.initials: D
authors.lastname: Jonas
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Meyer
authors.forename: Frank
authors.initials: F
authors.lastname: Schwab
authors.forename: Hajo
authors.initials: H
authors.lastname: Grundmann
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology*; D003428:Cross Infection / Q000382:microbiology; D024881:Drug Resistance, Bacterial / Q000187:drug effects / Q000235:genetics*; D004363:Drug Utilization; D014644:Genetic Variation; D005858:Germany; D006801:Humans; D015378:Imipenem / Q000494:pharmacology*; D007362:Intensive Care Units; D011446:Prospective Studies; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D018571:Sentinel Surveillance
chemical_list: D000890:Anti-Infective Agents; D002939:Ciprofloxacin; D015378:Imipenem