Impact of outpatient antibiotic use on carriage of ampicillin-resistant Escherichia coli.

Studies about the relationship between antibiotic consumption and carriage of antibiotic-resistant Escherichia coli in individual patients have yielded conflicting results. The goal of this study was to identify individual- and household-level factors associated with carriage of ampicillin (AMP)-resistant E. coli during consumption of a course of oral antibiotics. We enrolled outpatients and their families in a prospective household study of AMP-resistant or AMP-susceptible E. coli carriage. Two kinds of index patients were identified. Group 1 consisted of outpatients who were being initiated on a new antibiotic course at the time of a clinic visit, and group 2 consisted of outpatients not starting antibiotics. Each participant was asked to submit three stool swab samples (at baseline, week 1, and week 4) and to complete a questionnaire. Antimicrobial susceptibility testing was performed on each phenotypically distinct E. coli colony. The study included 149 group 1 households (total, 570 participants) and 38 group 2 households (total, 131 participants). AMP-resistant E. coli was recovered from 29% of stool samples. Observed associations with antibiotic exposure varied by drug class. Penicillins, which were the most frequently prescribed drug class, were associated with a modest increase in AMP-resistant E. coli carriage and a modest decrease in AMP-susceptible E. coli carriage. Neither change by itself was statistically significant. Macrolides were associated with reduced carriage of both AMP-resistant E. coli and AMP-susceptible E. coli (P < 0.05). Both AMP-resistant and AMP-susceptible E. coli demonstrated household clustering (P < 0.001). In summary, the overall effect of antibiotics on individual risk of carriage of AMP-resistant E. coli was small. However, even a modest alteration of the competitive balance between AMP-resistant and AMP-susceptible E. coli may promote population spread of resistant E. coli. Examining changes in both resistant and susceptible organisms in antibiotic-treated individuals and their close contacts improves understanding of antibiotic selection pressure.

Molecular analysis of antimicrobial-susceptible and -resistant Escherichia coli from retail meats and human stool and clinical specimens in a rural community setting.

BACKGROUND: Foodborne antimicrobial-resistant Escherichia coli may colonize and cause infections in humans, but definitive proof is elusive and supportive evidence is limited. METHODS: Approximately contemporaneous antimicrobial-resistant (n = 181) and antimicrobial-susceptible (n = 159) E. coli isolates from retail meats and from human stool and clinical specimens from a single rural U.S. community were compared for polymerase chain reaction (PCR)-defined phylogenetic group (A, B1, B2, or D) and virulence genotype. Meat and human isolates from the same phylogenetic group with similar virulence profiles underwent sequential two-locus sequence analysis, random amplified polymorphic DNA (RAPD) analysis, and pulsed-field gel electrophoresis (PFGE) analysis. RESULTS: According to phylogenetic distribution, resistant stool isolates were more similar to resistant meat isolates than to susceptible stool isolates. Overall, 19% of meat isolates satisfied molecular criteria for extraintestinal pathogenic E. coli (ExPEC). Nine sequence groups included meat and human isolates, and 17 of these 64 isolates demonstrated >80% RAPD profile similarity to an isolate from the alternate source group (meat vs. human). However, PFGE profiles of the 17 isolates were unique, excepting two stool isolates from the same household. CONCLUSION: Nearly 20% of meat-source resistant E. coli represented ExPEC. The observed molecular similarity of certain meat and human-source E. coli isolates, including antimicrobial-resistant and potentially pathogenic strains, supports possible foodborne transmission.

Mechanisms by which antibiotics promote dissemination of resistant pneumococci in human populations.

Mechanisms by which antimicrobials contribute to dissemination of pneumococcal resistance are incompletely characterized. A serial cross-sectional study of nasopharyngeal pneumococcal carriage in healthy, home-living children

Drug-resistant Escherichia coli, Rural Idaho.

Stool carriage of drug-resistant Escherichia coli in home-living residents of a rural community was examined. Carriage of nalidixic acid-resistant E. coli was associated with recent use of antimicrobial agents in the household. Household clustering of drug-resistant E. coli was observed. Most carriers of drug-resistant E. coli lacked conventional risk factors.

Clinical decision support and appropriateness of antimicrobial prescribing: a randomized trial.

CONTEXT: The impact of clinical decision support systems (CDSS) on antimicrobial prescribing in ambulatory settings has not previously been evaluated. OBJECTIVE: To measure the added value of CDSS when coupled with a community intervention to reduce inappropriate prescribing of antimicrobial drugs for acute respiratory tract infections. DESIGN, PARTICIPANTS AND SETTING: Cluster randomized trial that included 407,460 inhabitants and 334 primary care clinicians in 12 rural communities in Utah and Idaho (6 with 1 shared characteristic and 6 with another), and a third group of 6 communities that served as nonstudy controls. The preintervention period was January to December 2001 and the postintervention period was January 2002 to September 2003. Acute respiratory tract infection diagnoses were classified into groups based on indication for antimicrobial use. Multilevel regression methods were applied to account for the clustered design. INTERVENTION: Six communities received a community intervention alone and 6 communities received community intervention plus CDSS that were targeted toward primary care clinicians. The CDSS comprised decision support tools on paper and a handheld computer to guide diagnosis and management of acute respiratory tract infection. MAIN OUTCOME MEASURE: Community-wide antimicrobial usage was assessed using retail pharmacy data. Diagnosis-specific antimicrobial use was compared by chart review. RESULTS: Within CDSS communities, 71% of primary care clinicians participated in the use of CDSS. The prescribing rate decreased from 84.1 to 75.3 per 100 person-years in the CDSS arm vs 84.3 to 85.2 in community intervention alone, and remained stable in the other communities (P = .03). A total of 13,081 acute respiratory tract infection visits were abstracted. The relative decrease in antimicrobial prescribing for visits in the antibiotics "never-indicated" category during the post-intervention period was 32% in CDSS communities and 5% in community intervention-alone communities (P = .03). Use of macrolides decreased significantly in CDSS communities but not in community intervention-alone communities. CONCLUSION: CDSS implemented in rural primary care settings reduced overall antimicrobial use and improved appropriateness of antimicrobial selection for acute respiratory tract infections. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT00235703.