The objective of this study was to investigate the trends and patterns of resistance in ␤-lactamase-producing members of the family Enterobacteriaceae in a children's hospital over a 9-year period (1999 to 2007). Clinically significant isolates of the Enterobacteriaceae were screened for patterns of broad-spectrum resistance to ␤-lactams. The strains likely to be resistant were subsequently confirmed by an inhibitor-based disc test. The plasmid-mediated resistance determinants in these isolates were identified by PCR and by in vitro transformation, which successfully reproduced the AmpC phenotype unrestricted by the species of the host organisms. Among 8,048 Enterobacteriaceae isolates belonging to the four chromosomal ampC-negative or -nonfunctional genera, 86 (1.07%) isolates (56 Escherichia coli isolates, 22 Klebsiella species isolates, 1 Proteus mirabilis isolate, and 7 Salmonella species isolates) exhibited broad-spectrum ␤-lactam resistance patterns. These organisms collectively produced three classes of ␤-lactamases, including class A extended-spectrum ␤-lactamases (n ‫؍‬ 47), class C or AmpC ␤-lactamases (n ‫؍‬ 36, including 4 isolates that produced both class A and class C enzymes), and class A or B carbapenem-hydrolyzing ␤-lactamases (n ‫؍‬ 3). The proportion increased from 0.46% during the first 3 years to 1.84% during the last 3 years (relative risk [RR], 4.04; 95% confidence interval [CI], 2.28 to 7.42; P < 0.001). The increase was mainly due to the emergence of a plasmid-mediated bla CMY-2 ␤-lactamase, the incidence of which increased from 0.11% during the first 3 years to 0.96% during the last 3 years (RR, 9.11; 95% CI, 2.76 to 30.1; P ‫؍‬ 0.001). Class A-type resistance increased slightly during the study period, from 0.35% during the first 3 years to 0.85% during the last 3 years (RR, 2.42; 95% CI, 1.15 to 5.07; P ‫؍‬ 0.02). A Proteus mirabilis strain was documented to possess a novel bla DHA determinant. Of special concern, three carbapenemase-producing isolates were identified between 2003 and 2006. The infections caused by resistant isolates of the Enterobacteriaceae mainly affected hospitalized patients with underlying conditions; however, 19 (22%) episodes were of community onset in otherwise well children. The rate of resistance to broad-spectrum ␤-lactams among isolates of the Enterobacteriaceae is increasing in children in both hospitaland community-acquired settings, and the resistance is driven largely by plasmid-mediated AmpC ␤-lactamases. These data have important implications for empirical antimicrobial strategies targeting serious pediatric infections. Further study of this problem is warranted.The ever increasing variety of ␤-lactamases produced by isolates of the family Enterobacteriaceae raises concerns about our dependence on ␤-lactam drugs and the emergence of panresistant species. Rapidly emerging ␤-lactamases include extended-spectrum ␤-lactamases (molecular class A ␤-lactamases and, to a lesser extent, class D ␤-lactamases in the Enterobacteriaceae), AmpC ␤-lactamases (clas...

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Hospital mortality and hospital LOS of sepsis are similar to those reported in other observational studies. Our study confirms a decline in the mortality of sepsis predicted by earlier longitudinal studies and should prompt a resurgence of epidemiological research of the sepsis syndromes in the United States.

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