BALTIMORE — Antibiotic exposure within the previous 30 days increased the risk for an antimicrobial-resistant first-time urinary tract infection nearly fourfold in a retrospective cohort study of 533 healthy children aged 6 months to 6 years.
The finding suggests that clinicians should obtain a recent history of antimicrobial exposure in patients presenting with a new urinary tract infection (UTI) and select a different class of antibiotic for empiric therapy than the one the patient had previously received, Dr. Amanda A. Paschke said at the annual meeting of the Pediatric Academic Societies.
The children in the study had been diagnosed with their first UTI at one of 27 outpatient pediatric practices between July 1, 2001, and May 31, 2006. Most (92%) were female, two-thirds (60%) were white, and two-thirds (61%) were between the ages of 1 and 4 years. One-fifth (21%) had been exposed to antibiotics within the previous 120 days of the UTI, 14% within 60 days, and 8% within 30 days.
Otitis media was the most common indication for the prior antimicrobial prescriptions (51%), followed by sinusitis (11%), pharyngitis (10%), and dysuria (10%). “Many of the prescriptions were for indications that may not benefit from antibiotic treatment,” noted Dr. Paschke of Children's Hospital of Philadelphia.
The most common resistant organism was Escherichia coli (80%). Nearly half (46%) of the resistant infections were resistant to ampicillin, 17% to trimethoprim-sulfamethoxazole, and 15% to amoxicillin clavulanate, with less than 10% resistant to first- or third-generation cephalosporins.
Exposure to amoxicillin within the previous 0–30 days was associated with a nearly fourfold increased risk for an ampicillin-resistant UTI (adjusted odds ratio, 3.6), as well as for a UTI with resistance to amoxicillin clavulanate (adjusted OR, 3.9). Exposure to amoxicillin within 31–60 days increased the risk for an ampicillin-resistant UTI by 2.8-fold.
The predicted probability of an ampicillin-resistant UTI was 67% within 30 days of exposure to amoxicillin, 62% within 60 days, and 38% beyond 60 days. The predicted probability of amoxicillin clavulanate resistance was 37% within 30 days of exposure and was relatively low (13%–15%) beyond 60 days, Dr. Paschke said.
In addition to avoiding prescribing the same antimicrobial to treat a new infection that a patient recently received for a previous infection, she recommended other strategies to limit antimicrobial resistance: Use a “wait and see” prescription approach for acute otitis media, prescribe the narrowest-spectrum antimicrobials possible, use short-course antimicrobial regimens when appropriate, and avoid antimicrobials altogether for indications such as most upper respiratory infections for which antimicrobials are unlikely to be of benefit, she advised.
Dr. Paschke stated that she had no relevant conflicts of interest.