The effect of age on outpatient uropathogen antibiotic resistance

Abstract

Study objectives: Empiric antibiotic treatment of urinary tract infection (UTI) in adults is based on the local resistance patterns of common uropathogens. Increasing antibiotic resistance has affected empiric antibiotic choice for UTI. Most antibiotic resistance levels report overall inpatient resistance, and there are limited data on outpatient resistance trends. We describe the effect of age on outpatient resistance patterns to common empiric antibiotics. Methods: This is a multicenter, prospective case series composed of patients with UTI. Participating facilities include 4 emergency departments and 84 outpatient clinics in an urban and suburban environment. All urine samples were collected during a 12-month period from July 2002 through June 2003. Only adult patients with a clean-catch urine containing greater than 100,000 colony-forming units of a uropathogen were included. Uropathogens were tested against levofloxacin, ceftriaxone, trimethoprim/sulfamethoxazole (TMP/SMX), and ampicillin. Resistance data were divided into 5 age groups: 18 to 40, 41 to 50, 51 to 60, 61 to 70, and older than 70 years. Results: Two thousand seven hundred fifty-one total urine cultures met inclusion criteria. The 2 most common uropathogens were Escherichia coli (52% to 76%) and Enterococcus sp (11% to 20%) in all age groups. Older patients were less likely to have a UTI caused by E coli. E coli resistance to ceftriaxone and ampicillin varied little across age (0.2% and 32%, respectively), with the exception of patients older than 70 years, where E coli resistance to ampicillin decreased to 23%. E coli resistance to levofloxacin showed nonlinear relationships to age, with the highest resistance seen in the sixth decade (0.76% to 4.55%). E coli resistance to TMP/SMX decreased with advancing age (14.8% in young adults to 11.5% in adults >70 years). The number of UTIs caused by Enterococcus sp increased with advancing age, with older patients having higher resistance to levofloxacin (5.7% in young adults compared with 33% in adults >70 years). Enterococcus sp resistance to ampicillin varied across age groups, with the highest resistance seen in adults older than 70 years (0.0% to 9.2%). Enterococcus sp was not tested against TMP-SMZ or ceftriaxone. Conclusion: Outpatient uropathogen antibiotic resistance was affected by patient age. Enterococcus sp resistance increased as patient age increased. Empiric antibiotic coverage in the elderly should take into consideration the possibility of higher levels of fluoroquinolone resistance in patients with a Gram-positive UTI.