Antibiotic Resistance Differs with Sex in Older Adults with UTIs

The sex of the patient should factor into a prescriber’s choice of antibiotic to treat urinary tract infection (UTI) in older adults, suggests a study in the recent BMC Geriatrics.

Researchers from the University of Oslo and the Vestfold Hospital Trust (Oslo, Norway) analyzed 3786 urine cultures positive for bacteria from patients age 65 and older. At first, they compared cultures between older adults who lived in nursing homes and those who lived in the community to see if separate antibiotic recommendations were warranted. Their findings were lackluster. On the whole, there was no significant difference in the proportions of any of the bacteria between the groups, with Escherichia coli the most common and Escherichia faecalis the second most common. For both groups, E. coli resistance rates were more than 20% for ampicillin and trimethoprim, and E. faecalis resistance rates were more than 20% for trimethoprim. 

Then the researchers, led by Mark Fagan, looked at differences between men and women irrespective of residence.

“The differences between bacterial etiology and resistance rates among uropathogens isolated from elderly patients living in a nursing home and those living in the community were clinically unimportant,” the authors reported. “There is, however, a significant and clinically relevant difference between males and females both in terms of bacterial etiology and resistance rates.”

E. coli was significantly more common in the infections of women, they found, and E. faecalis was significantly more common in men with UTIs.

Regarding rates of antibiotic resistance, researchers found significantly higher resistance of E. coli to ciprofloxacin and of Proteus mirabilis to mecillinam in older men. They found no significant differences between men and women in resistance to E. faecalis, Klebsiella pneumoniae, or Pseudomonas aeruginosa. 

For older women, the theoretic risk of treatment failure was more than 20% for ampicillin and trimethoprim, indicating that they may be poor choices for UTI treatment, researchers wrote. Older men, on the other hand, may benefit from trimethoprim therapy, because researchers found lower rates of E. coli resistance to that antibiotic in men. 

In older men, the theoretical risk of failure was more than 20% for ampicillin, ciprofloxacin, and mecillinam, indicating that these antibiotics are potentially poor choices for that group (https://www.biomedcentral.com/1471-2318/15/98).

“Differences in resistance rates for patients in the nursing home do not warrant separate recommendations for empiric antibiotic therapy,” the researchers concluded, “but recommendations based on gender seem warranted.”—Jolynn Tumolo