title: Microbiological screening is necessary to distinguish carriers of plasmid-mediated AmpC beta-lactamase-producing enterobacteriaceae and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae because of clinical similarity.
abstract: OBJECTIVE
  Plasmid-mediated AmpC beta-lactamase-producing (pAmpC) Enterobacteriaceae are increasing worldwide, difficult to identify and often confounded with extended-spectrum beta-lactamase (ESBL) producers. The low prevalence precludes routine universal admission screening. Therefore, we evaluated potential risk factors for carriage of pAmpC-producing Enterobacteriaceae that would allow targeted screening to improve yield and reduce cost.
  
  
  METHODS
  We performed a case control study at a tertiary care center from 1/2006 to 12/2010. Cases were adult patients in whom pAmpC-producing Enterobacteriaceae were isolated; controls were chosen among carriers of ESBL-producing Enterobacteriaceae. Both infected and colonized patients were included.
  
  
  RESULTS
  Over five years, we identified 40 pAmpC producers in 39 patients among 16,247 screened consecutive isolates of Enterobacteriaceae. The pAmpC prevalence was low (0.25%), but more than 30% of pAmpC carriers received incorrect empirical antibiotic treatment. When compared with 39 ESBL controls, pAmpC carriage was associated with clinically confirmed infections in 74% (versus 51%) (p=0.035), mainly of the urinary tract, previous antibiotic exposure in 63% (versus 36%) (p=0.035) and carriage of a nasogastric tube in 23% (versus 0%) (p=0.002). In the multivariate regression analysis only clinically confirmed infections remained significantly associated with pAmpC carriage (OR 1.44 (95%CI 1.15-2.57)). No other clinical and blood test-associated risk factor allowed discrimination of pAmpC-carrying patients from ESBL controls. The type of acquisition - nosocomial versus community-acquired - was also non-informative for resistance type, as 46% of pAmpC- and 44% of ESBL-producing Enterobacteriaceae were community-acquired.
  
  
  CONCLUSIONS
  This study could not identify a clinical profile that would allow targeted screening for pAmpC-producing Enterobacteriaceae when compared to ESBL carriers. Because empiric antimicrobial therapy was inappropriate in more than 30%, rapid identification of pAmpC carriers is needed. New microbiological methods are therefore required to simplify rapid and reliable detection of pAmpC carriers.
authors: Division of Infectious Diseases and Hospital Epidemiology, Kantonsspital Aarau, Aarau, Switzerland.
authors: Anna
authors: A
authors: Conen
authors: Division of Clinical Microbiology, University Hospital Basel, Basel, Switzerland; Division of Infectious Diseases and Hospital Epidemiology, University Hospital Basel, Basel, Switzerland.
authors: Reno
authors: R
authors: Frei
authors: Division of Clinical Microbiology, University Hospital Basel, Basel, Switzerland.
authors: Hildegard
authors: H
authors: Adler
authors: Division of Infectious Diseases and Hospital Epidemiology, University Hospital Basel, Basel, Switzerland.
authors: Marc
authors: M
authors: Dangel
authors: Division of Infectious Diseases and Hospital Epidemiology, Kantonsspital Aarau, Aarau, Switzerland.
authors: Christoph A
authors: CA
authors: Fux
authors: Division of Infectious Diseases and Hospital Epidemiology, University Hospital Basel, Basel, Switzerland.
authors: Andreas F
authors: AF
authors: Widmer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001426:Bacterial Proteins / Q000378:metabolism*; D002353:Carrier State / Q000175:diagnosis* / Q000382:microbiology; D016022:Case-Control Studies; D004755:Enterobacteriaceae / Q000201:enzymology* / Q000302:isolation & purification*; D004756:Enterobacteriaceae Infections / Q000175:diagnosis* / Q000382:microbiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010957:Plasmids / Q000378:metabolism*; D055815:Young Adult; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C048795:AmpC beta-lactamases; D001618:beta-Lactamases