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The Importance of Addressing Multidrug Resistance and Not Assuming Single-Drug Resistance in Case-Control Studies

Published online by Cambridge University Press:  21 June 2016

Erika M. C. D'Agata ,
Maria Adriana Cataldo ,
Roberto Cauda  and
Evelina Tacconelli
Erika M. C. D'Agata*
Affiliation:
Division of Infectious Diseases, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
Maria Adriana Cataldo
Affiliation:
Department of Infectious Diseases, Catholic University, Rome, Italy
Roberto Cauda
Affiliation:
Department of Infectious Diseases, Catholic University, Rome, Italy
Evelina Tacconelli
Affiliation:
Division of Infectious Diseases, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts Department of Infectious Diseases, Catholic University, Rome, Italy
*
Beth Israel Deaconess Medical Center, Division Infectious Diseases, 330 Brookline Avenue, East Campus Mailstop SL-435G, Boston, MA 02215 (edagata@bidmc.harvard.edu)
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Abstract

Background.

Case-control studies analyzing antibiotic exposure as a risk factor for antimicrobial resistance usually assume single-drug resistance in the bacteria under study, even though resistance to multiple antimicrobials may be present. Since antibiotic selection pressures differ depending on the susceptibility profile of the antimicrobial-resistant bacteria, an accurate assessment of whether exposure to an individual antimicrobial is a risk factor for the emergence of resistance should distinguish between single-drug–resistant and multidrug-resistant bacteria.

Objective.

To determine whether the exposures to individual antibiotics that were identified as independent risk factors in case-control studies differed depending on whether single-drug–resistant or multidrug-resistant bacteria were evaluated.

Design.

Two retrospective case-control studies were performed with data on patients harboring Pseudomonas aeruginosa strains resistant only to ciprofloxacin (CRPA) and patients harboring P. aeruginosa strains resistant to ciprofloxacin and other antibiotics (multidrug-resistant P. aeruginosa [MDR-PA]). These 2 groups were compared with patients not harboring P. aeruginosa.

Setting.

Two tertiary care hospitals.

Results.

A total of 41 patients harboring CRPA and 151 patients harboring MDR-PA were identified and matched to 192 control subjects. By conditional logistic regression, independent risk factors associated with presence of CRPA were nonambulatory status (OR, 5.6 [95% confidence interval {CI}, 1.4-23]; P = .02) and prior ciprofloxacin exposure (OR, 5.0 [95% CI, 1.2-21]; P = .03). Independent risk factors for presence of MDR-PA were a Charlson score greater than 2 (OR, 3.3 [95% CI 1.8-6.0]; P<.001) and exposure to quinolones (OR, 2.8 [95% CI, 1.2-5.0]; P = .001), third- and fourth-generation cephalosporins (OR, 3.5 [95% CI, 1.7-7.1]; P<.001), imipenem (OR, 3.8 [95% CI, 1.2-12.1]; P = .02), and/or aminoglycosides (OR, 2.3 [95% CI, 1.04-5.1]; P = .04).

Conclusion.

There were substantial differences in exposure to individual antimicrobials between patients harboring CRPA and patients harboring MDR-PA. Future case-control studies addressing risk factors for single-drug–resistant bacteria should consider the complete susceptibility profile of the bacteria under investigation.

Type
Original Articles
Information
Infection Control & Hospital Epidemiology , Volume 27 , Issue 7 , July 2006 , pp. 670 - 674
Copyright
Copyright © The Society for Healthcare Epidemiology of America 2006

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