Screening rectal culture to identify fluoroquinolone-resistant organisms before transrectal prostate biopsy: Do the culture results between office visit and biopsy correlate?

Objective: To investigate the performance of screening rectal cultures obtained 2 weeks before transrectal prostate biopsy to detect fluoroquinolone-resistant organisms and again at transrectal prostate biopsy. Materials and Methods: After institutional review board approval for observational study, we obtained a rectal culture on patients identified for a prostate biopsy but before antibiotic prophylaxis from September 12, 2011 to April 23, 2012. The specimen was cultured onto MacConkey agar with and without 1 μg/mL ciprofloxacin. We then obtained a second rectal culture immediately before prostate biopsy after 24 hours of ciprofloxacin prophylaxis. All cultures were blinded to the practitioner until the end of the study. Results: Of 108 patients enrolled, 58 patients had both rectal cultures for comparison. The median time duration between cultures was 14 (6-119) days. There were 54 of 58 concordant pairs (93%), which included 47 negative cultures and 7 positive cultures; 2 patients (3%) who were culture negative from the first screening culture became positive at biopsy. Sensitivity, specificity, negative, positive predictive values, and area under the operator curve were 95.9%, 77.8%, 95.9%, 77.8%, and 0.868, respectively. When Pseudomonas spp. are removed from the analysis, the area under the curve is increased to 0.927. Conclusion: Screening rectal cultures 2 weeks before prostate biopsy has favorable test performance, suggesting screening cultures give an accurate estimate of fluoroquinolone- resistant colonization.