Abstract
ObjectivesPlasmid-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.Patients and methodsWe 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.ResultsOver 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.ConclusionsThis 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.
Highlights
Multidrug-resistant Enterobacteriaceae (MRE) are rapidly emerging worldwide and account for a large proportion of health care-associated infections [1]
When compared with 39 extended-spectrum beta-lactamases (ESBL) controls, plasmidmediated AmpC (pAmpC) carriage was associated with clinically confirmed infections in 74% (p=0.035), mainly of the urinary tract, previous antibiotic exposure in 63% (p=0.035) and carriage of a nasogastric tube in 23%
In the multivariate regression analysis only clinically confirmed infections remained significantly associated with pAmpC carriage (OR 1.44 (95%confidence intervals (CI) 1.15-2.57))
Summary
Multidrug-resistant Enterobacteriaceae (MRE) are rapidly emerging worldwide and account for a large proportion of health care-associated infections [1]. And less well documented is resistance to broad spectrum cephalosporins by plasmidmediated AmpC (pAmpC). PAmpC producers were first described in 1989. They have descended from campC genes and fall into six phylogenetic groups. PAmpC are known to exist in various species lacking inducible campC genes including Klebsiella spp., Proteus mirabilis, Salmonella enterica and Shigella spp. Some strains negative for campC or those that almost never express cAmpC, may acquire pampC genes rendering them resistant to these cephalosporins [4]. In a recent publication from Germany, more than 50% of healthy broiler chicken were carriers of pAmpC-producing Enterobacteriaceae, potentially serving as reservoir for spread [9]. A recent Swiss study demonstrated a high prevalence of pAmpC in patients from specialized outpatient clinics (12.5%) [15]
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