SAN FRANCISCO — The culprit behind most noncomplicated urinary tract infections in outpatients—Escherichia coli—plays less of a role as patients age, a study of 2,751 urine cultures showed.
Other pathogens, particularly enterococcus, played a greater role in urinary tract infections (UTIs) in older patients, and the rates of antibiotic-resistant enterococcus increased in older patients, David J. Blehar, M.D., said at the annual meeting of the American College of Emergency Physicians.
The prospective study of serial cases from 80 outpatient offices and four emergency departments divided adult patients into five age groups and looked at the pathogens responsible for UTIs and their susceptibility to antibiotic treatment.
In the youngest group, 18- to 40-year-olds, E. coli caused more than 75% of UTIs, a finding similar to previous estimates that E. coli causes 75%–90% of UTIs overall. The role of E. coli fell with increasing age, however, with a proportional increase in other pathogens. In patients older than 80 years, E. coli accounted for fewer than half of UTIs, but enterococcus caused up to 20% of UTIs, said Dr. Blehar of the University of Massachusetts, Worcester.
The study looked at rates of resistance to four antibiotic therapies. Although trimethoprim/sulfamethoxazole (TMP/SMX) is the formal first-line drug therapy for noncomplicated UTI, guidelines suggest substituting a fluoroquinolone in areas where rates of E. coli resistance to TMP/SMX exceed 10%–20%. Dr. Blehar's institution and others have adopted the fluoroquinolone levo-floxacin as first-line therapy for noncomplicated UTIs. The study also looked at ceftriaxone and ampicillin resistance.
E. coli generally maintained susceptibility to the various antibiotics across age groups, except for a statistically nonsignificant trend toward greater resistance to TMP/SMX with increasing age. Pathogen resistance to ceftriaxone or ampicillin also held steady across age groups.
While E. coli resistance rates to levo-floxacin remained low across age groups, enterococcus resistance rates climbed with age. In patients aged 70 years or older, 22% of enterococci were resistant to levofloxacin, and 38% of enterococci showed resistance to levofloxacin in patients aged 80 years and older.
“Urine Gram stain is not a routine study done in our institution, but it may be warranted in this subset of patients to aid in the work-up of UTI,” Dr. Blehar said. “If gram-positive UTI is identified, we would add additional coverage for enterococcus.”