Rectal colonization with fluoroquinolone-resistant Escherichia coli before a transrectal prostate biopsy was associated with a post-procedure infection when ciprofloxacin monotherapy is used for prophylaxis, researchers at the Veterans Affairs Healthcare System in San Diego have found.
“Measures to prevent rectal colonization with fluoroquinolone-resistant E. coli, and/or to detect such strains in advance of [transrectal prostate biopsy (TPB)] so that antibiotic prophylaxis can be adjusted appropriately, could help reduce the considerable morbidity and costs associated with post-TPB infection,” the researchers wrote in Clinical Infectious Diseases.
The researchers conducted an observational cohort study of 914 men who underwent a pre-TPB rectal culture from Jan. 1, 2010 to Feb. 6, 2014. Clinical data were available for 764 of the biopsies, of which 121 identified a fluoroquinolone-resistant organism. Twenty-one patients developed a urinary tract infection and presented to the ED within 72 hours of the biopsy. Among them, 13 patients (62%) had fluoroquinolone-resistant E. coli on their pre-TPB rectal culture.
The infections in all of these patients, and one non-colonized patient, were due to fluoroquinolone-resistant E. coli. The remaining seven patients were infected with other fluoroquinolone-susceptible bacteria or had a sterile urine culture. In a multivariable analysis, colonization with fluoroquinolone-resistant E. coli (OR=4.5; 95% CI, 1.2-18.2) and hospitalization in the previous year for any cause (OR=4.5; 95% CI, 1.1-19.4) were significantly associated with risk for post-TPB infection.
Eighty-one of the fluoroquinolone-resistant E. coli rectal isolates underwent molecular analysis. Eleven of the 81 patients developed post-TPB. ST131 frequency in rectal isolates was similar among those who developed infection and the other 70 patients. Nine of the 11 patients had clinical and rectal isolates for genomic comparison. Each pair had identical PGFE profiles and antimicrobial susceptibility.
“This molecular analysis provides, to our knowledge, the first direct evidence for the long-held but untested assumption that the patient’s own rectal microbiota is the source of most post-TPB infections,” the researchers wrote. “In turn, this suggests that rectal bacteria are implanted directly from the rectum into the blood, urine, and/or prostate by the prostate biopsy needle, and that the fluoroquinolone-resistant E. coli strains that are destined to cause post-TPB infection can be reliably identified in advance by rectal culture.”
Disclosure: One researcher has received grants or consultancies from ICET, Merck, Syntiron and Tetraphase.