Laurie Barclay, MD

June 30, 2008

June 30, 2008 — Resistance of uropathogenic Escherichia coIi to ciprofloxacin among college students has doubled since 1999, although trimethoprim/sulfamethoxazole (TMP-SMX) resistance has changed little, according to the results of a study reported at the 2008 Annual Conference on Antimicrobial Resistance in Bethesda, Maryland.

"Urinary tract infections [UTIs], a common bacterial infection, are frequently caused by E coli; these infections are usually treated empirically without culture," presenter and lead author Cibele Barbosa-Cesnik, MD, MPH, a research investigator in the Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, told Medscape Infectious Diseases. "Therefore, regular monitoring of antibiotic resistance profile in the community is crucial in order to prescribe appropriate therapy."

Between September 2005 and June 2007, the investigators collected E coli isolates from women with uncomplicated cystitis who were participating in a clinical trial, and they tested antibiotic susceptibility for all unique isolates from each individual, using a Vitek 2 (bioMerieux, Inc) automated system. There were 63 isolates tested for resistance to 18 antimicrobial drugs in year 1 (2005 – 2006) and 139 isolates tested in year 2 (2006 – 2007).

Resistance to more than 1 drug was present in 37% of isolates, 27% of isolates were resistant to more than 2 drugs, and 17% of isolates were resistant to more than 3 drugs. Resistance to ampicillin was found in 32% of isolates, tetracycline in 19%, TMP-SMX in 17%, piperacillin in 11%, cefazolin and ciprofloxacin in 3%, and gentamicin, levofloxacin, and amoxicillin-clavulanic acid in 2%.

Overall resistance patterns were similar in year 1 and year 2, but resistance to TMP-SMX was higher in year 1 than in year 2 (22% vs 14%).

On the basis of these findings, the authors concluded that TMP-SMX resistance in the same study population has changed little since 1999, when it was 15.8%, but that resistance to ciprofloxacin had doubled during the same time frame. Although the authors found that the slow rate of increase in TMP-SMX resistance among urinary isolates in the same geographic area during a 6-year period was reassuring, they suggest that the long-term utility of TMP-SMX as a first-line treatment of UTI is in doubt.

"Before prescribing empiric antibiotic therapy for UTI — or any other infection, as a matter of fact — make sure you are up to date with the most current antibiotic resistance profile for your community," Dr. Barbosa-Cesnik said. "If that is not available, it is always wise to request a urine culture with antibiotic sensitivity test."

When asked to review the strengths and limitations of this study, Jack D. Sobel, MD, professor and chief of infectious disease at Wayne State University School of Medicine in Detroit, Michigan, told Medscape Infectious Diseases that "the study is relatively small, but large enough to be relevant."

"The study is right on target and reflects what other investigators have recently observed," said Dr. Sobel, who was not directly involved with this study. "The increase in quinolone resistance, although still quite low, is alarming."

Dr. Barbosa-Cesnik and Dr. Sobel have disclosed no relevant financial relationships.

2008 Annual Conference on Antimicrobial Resistance: Poster P21. June 23–25, 2008.


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