Nearly one-half of the patients who presented to the emergency department with diarrhea had a definite or plausible pathogen in their stool specimens. We were unable to develop a model that was substantially better than physician judgment in identifying patients for whom bacterial culture would yield positive results. The unexpectedly high rate of C. difficile toxin warrants further examination.

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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...

The bacterial diarrhea prevalence is similar to that in other ambulatory studies, although the spectrum differs. Exclusion criteria for stool testing in diarrhea remain elusive. Studies to determine the etiology of unexplained diarrhea and cost-effective algorithms for diarrhea diagnosis, are needed.

Cystic fibrosis (CF) patients are predisposed to chronic respiratory infection by nonfermentative gramnegative bacilli, including Stenotrophomonas maltophilia. S. maltophilia is highly resistant to most antibiotics, with the exception of sulfamethoxazole-trimethoprim (SXT). SXT-resistant S. maltophilia has been reported, but the mechanism of resistance is not well defined. Repeated findings of suspected small-colony-variant (SCV) S. maltophilia isolates from the sputa of five CF patients were confirmed by partial 16S rRNA gene sequencing. The SCV S. maltophilia isolates were the only S. maltophilia isolates in these cultures, and none were clonally related. DNA fingerprint analysis confirmed that once established, the SCV S. maltophilia strains persisted. Nutritional studies of SCV S. maltophilia have suggested auxotrophy in hemin, methionine, and thymidine associated with resistance to multiple antibiotics, including SXT. The phenotypic switch from wild-type to SCV S. maltophilia was reproducible in vitro by exposure to SXT, suggesting that prolonged exposure to antibiotics may select for both the SCV S. maltophilia phenotype and SXT resistance by interference with the dihydrofolate reductase pathway. Recovery of SCV S. maltophilia from the sputum of CF patients has implications for both laboratory testing and patient management.

The extent to which antibiotic-resistant bacteria are excreted by humans who have not been exposed to antibiotics is not known. Children, who rarely receive fluoroquinolones, provide opportunities to assess the frequency of fecal excretion by fluoroquinolone-naïve hosts of fluoroquinolone-resistant gram-negative bacilli. Fresh nondiarrheal stools from children were processed by screening them on agar containing ciprofloxacin to recover ciprofloxacin-resistant gram-negative bacilli. Resistant isolates were identified, and ciprofloxacin MICs were determined. Resistant Escherichia coli isolates were also analyzed for urovirulence-associated loci. Thirteen (2.9%) of 455 stools yielded ciprofloxacin-resistant E. coli (seven children), Stenotrophomonas maltophilia (four children), and Achromobacter xylosoxidans and Enterobacter aerogenes (one child each). Neither the subjects themselves nor members of their households used fluoroquinolones in the 4 weeks preceding collection. Six of the seven resistant E. coli isolates belonged to phylogenetic groups B2 and D, in which extraintestinal pathogenic E. coli bacteria are frequently found. All resistant E. coli isolates contained at least three putative E. coli virulence loci. Most ciprofloxacin-resistant bacteria were resistant to additional antibiotics. Potentially pathogenic bacteria that are resistant to therapeutically important antimicrobial agents are excreted by some humans, despite these persons' lack of exposure to the particular drugs. The sources of these resistant organisms are unknown. This underrecognized reservoir of drug-resistant potential pathogens poses public health challenges.

Timely accurate diagnosis of Shiga toxin-producing Escherichia coli (STEC) infections is important. We evaluated a laboratorydeveloped real-time PCR (LD-PCR

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