Large study supports pre-prostate biopsy rectal cultures

Editor's note: This article has been updated since its original publication to include additional study data and commentary from the author/presenter.

Orlando, FL-Rectal colonization with a fluoroquinolone-resistant (FQR) organism identifies men who are at significantly increased risk for an infectious complication following prostate biopsy, according to the findings of a recent multi-institutional international collaborative study.

The investigation, which was conceived by first author Michael Liss, MD, was a retrospective analysis of several prospective studies investigating men who had a rectal swab for culture prior to prostate biopsy but whose antibiotic prophylaxis was not guided by the culture results. Six institutions participated and provided data for 2,673 men whose procedures were performed from 2007 through 2013.

Of the overall population, 92% of men received a fluoroquinolone for prophylaxis and 27% received an augmented regimen that included additional antibiotics. About 20% of men had an FQR-positive rectal culture, 2.6% developed a post-biopsy infection, and 1.6% had an infection-related hospitalization.

Compared to men whose rectal culture was negative for an FQR organism, those who were FQR culture positive had a significantly higher rate of infection (6.6% vs. 1.6%) and hospital admission for infection (4.4% vs. 0.9%). The associations were more pronounced when considering men who received antibiotic prophylaxis with only a fluoroquinolone (1,876 men). In the latter subgroup, the infection rate was 8.2% among men who were FQR positive versus 1.8% in those who were FQR negative, and the rates of infection-related hospital admission in the FQR-positive and FQR-negative men were 6.1% and 1.1%, respectively.

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Results of multivariate regression analyses showed that in the population overall, an FQR-positive rectal culture predicted a fourfold increased risk of infection and a nearly fivefold increased risk of hospitalization for infection. Among men who received a fluoroquinolone as monotherapy for prophylaxis, FQR-positive status increased the risk of infection by 4.7-fold and the risk of infection-related hospitalization 5.7 times, reported Dr. Liss, clinical instructor in urology at the University of California, San Diego.

Dr. Liss“The growing problem of bacterial resistance to fluoroquinolones has created concern about infection following prostate biopsy and led some centers to advocate use of targeted antibiotic prophylaxis guided by the findings from a pre-biopsy rectal culture. Results from a few small, nonrandomized studies provide some evidence to support this practice. However, there has been limited, underpowered research to show that rectal colonization with an FQR organism increases infection risk,” said Dr. Liss, who presented the findings at the AUA annual meeting in Orlando, FL.

Rectal culture could guide prophylaxis

“I am excited to present our findings because based on its size, we believe our study provides the most definitive data on post-biopsy infection risk according to FQR colonization status to date. Our results support performing pre-biopsy rectal swab culture in all men undergoing prostate biopsy in which fluoroquinolone prophylaxis is planned. The result may allow the urologist to consider an augmented prophylaxis or alternative prophylaxis in those who are FQR culture positive, because they are definitely at increased risk for post-biopsy infection. Further studies are needed to establish the efficacy of targeted prophylaxis guided by rectal culture.”

The institutions included in the study represented two centers from the United States and one each from Belgium, Canada, England, and Thailand. Dr. Liss acknowledged that the study has limitations related to variations in protocols across the centers, which include differences in culture technique (use of selective or non-selective media), method for identifying complications (chart review or phone contact), types of baseline demographic and clinical data collected, and standard prophylactic regimen used.

To minimize the potential for geographic bias, data points were included in the risk analyses only if there was information available on them for at least 75% of men. Using this threshold, age, race/ethnicity, body mass index, diabetes, PSA, prostate size on ultrasound, use of bowel preparation, method of follow-up (chart review, phone contact), antibiotic augmentation (two or more antibiotics), and FQR-positive culture were analyzed for their potential association with infection.

The multivariate analyses controlled for bowel prep and presence of diabetes, as these factors increased risk of hospitalization for infection in univariate analysis.UT

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