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.
Division of Epidemiology, Department of Internal Medicine, University of Utah School of Medicine, Salt Lake City, UT 84132, USA. Matthew.Samore@hsc.utah.edu
Matthew H
MH
Samore
Claude
C
Tonnerre
Elizabeth Lyon
EL
Hannah
Gregory J
GJ
Stoddard
Robert J
RJ
Borotkanics
Bassam
B
Haddadin
Stephan
S
Harbarth
D000293:Adolescent; D000667:Ampicillin / Q000627:therapeutic use*; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D002648:Child; D002675:Child, Preschool; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000188:drug therapy* / Q000453:epidemiology / Q000382:microbiology; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D010045:Outpatients
D000900:Anti-Bacterial Agents; D000667:Ampicillin