Clinical and microbiological determinants of infection after transrectal prostate biopsy

Background. Increasing numbers of infections following transrectal prostate biopsy (TPB) at our hospital led us to investigate clinical and bacterial risk factors to determine if the colonizing rectal Escherichia coli population is the source. Methods. We performed an observational cohort study of men undergoing TPB (1 January 2010-6 February 2014) at the San Diego Veterans Affairs Medical Center. The primary outcome was clinically significant post-TPB infection. Rectal swabs were collected immediately before the biopsy and cultured selectively for fluoroquinolone-resistant gram-negative bacilli. Fluoroquinolone-resistant clinical and rectal E. coli isolates were compared using phylotyping, pulsed-field gel electrophoresis (PFGE) analysis, sequence typing, and virulence gene profiling. Results. Rectal colonization with fluoroquinolone-resistant organisms (98% E. coli) was detected in 121 of 764 subjects (15.8%). Post-TPB infection was more common among fluoroquinolone-resistant-colonized subjects than noncolonized subjects (13/121 [10.7%] vs 8/649 [1.2%]; P <. 001). Presence of fluoroquinolone-resistant colonizing E. coli was the most significant host characteristic associated with post-TPB infection (odds ratio, 4.5 [95% confidence interval, 1.2-18.2]; P =. 03). Escherichia coli infection isolates (n = 18) did not differ from E. coli rectal culture isolates (n = 68) for any of 49 virulence genes or ST131 status (all P >. 05). The rectal and clinical isolates of all 9 men with paired isolates had indistinguishable PFGE patterns and identical antimicrobial susceptibility profiles. Conclusions. The rectal colonizing E. coli population is the source for most fluoroquinolone-resistant post-TPB infections, regardless of clonal background or virulence traits. Screening cultures can identify nearly all patients at risk for fluoroquinolone-resistant post-TPB infection.