Re-evaluation of Antimicrobial Resistance Patterns 7 Years after Change in Institutional Guidelines for Uncomplicated Cystitis.

Background: The Infectious Disease Society of America (IDSA) guidelines recommend the use of nitrofurantoin (NF) among the first line treatments of uncomplicated urinary tract infection (UTI) due to its narrow spectrum of activity and decreased risk of ecological adverse effects. Through a retrospective cohort study, we investigated the impact of an antibiotic stewardship program recommending NF on antibiotic resistance patterns and risk factors associated with NF resistance, seven years after its implementation.

Methods: UTIs due to E. coli in non-pregnant adults in ambulatory settings were identified using warehoused data from January 2008- December 2014. Rates of E. coli resistance to levofloxacin (LV) and NF were characterized over this time, as were prescribing patterns for LV and NF. In a case control retrospective cohort, NF resistant E. coli isolates were identified as cases and NF susceptible controls were matched 2:1. The risk factors assessed for antibiotic resistance via manual chart review included chronic comorbid medical illness, prior antibiotic exposure and recent surgical procedure. Chi square test assessed for statistical significance.

Results: 2,104 E. coli positive UTIs were identified, 38 meeting inclusion criteria were resistant to NF. Having had a prior surgical procedure reached statistical significance (OR 3.25, P=0.04). Diabetes and prior NF use had non-significant trends towards NF resistance. NF prescribing increased from 3.53 to 4.01 per 1,000 outpatient visits, while E. coli resistance remained stable at 2%. LV prescribing fell from 4.76 to 3.2 prescriptions per 1,000 outpatient visits, and E. coli resistance to LV increased from 13% to 15%. NF resistant isolates also had lower rates of resistance to other antibiotics when compared to LV resistant isolates. 

Conclusion:  NF remains an acceptable first line treatment for uncomplicated UTI with little risk for resistance, and when resistance does occur it is less likely to be associated with resistance to other antibiotics. This supports the continued use of antibiotic stewardship programs recommending narrow spectrum antibiotics as seen by NF’s stable resistance rate despite increased prescribing as compared to LV’s continued rise in resistance despite decreases in use.