By Richard R. Watkins, MD, MS, FACP

Division of Infectious Diseases, Akron General Medical Center, Akron, OH; Associate Professor of Internal Medicine, Northeast Ohio Medical University, Rootstown, OH

Dr. Watkins reports that he has received research support from Forest Laboratories.

SYNOPSIS: An observational cohort study found that rectal colonizing strains of E. coli are the source for most fluoroquinolone-resistant post-transrectal prostate biopsy infections. Pre-procedure screening cultures should be considered.

SOURCE: Liss MA, et al. Clinical and microbiological determinants of infection after transrectal prostate biopsy. Clin Infect Dis 2015;60:979-987.

The incidence of infections following transrectal prostate biopsy (TPB) has been increasing, especially from strains of fluoroquinolone-resistant Escherichia coli. This has led some urologists to try alternative approaches to traditional fluoroquinolone prophylaxis, such as pre-procedural rectal swab cultures to guide individual antibiotic selection. Liss and colleagues investigated whether these colonizing rectal E. coli strains were associated with TPB infections.

The study was conducted at the San Diego Veterans Affairs Medical Center between January 1, 2010, and February 6, 2014. Patients who were undergoing TPB had a pre-procedure rectal culture done as part of a quality-improvement program. After the procedure, the patients were followed for post-TPB infections, defined as a presentation to the emergency department with lower urinary tract symptoms, fever, and/or chills within 7 days of the TPB. These clinical isolates of the patients with infections were captured for genetic analysis. The association of fluoroquinolone-resistant E. coli rectal colonization with post-TPB infection was determined by comparing the infection rate among carriers to noncarriers. Clonal similarity was assessed between the pre-TPB rectal culture and the post-TPB infection culture. The characteristics that distinguished infectious isolates from colonizing isolates were elucidated using a subset of colonization isolates. These were obtained from patients who did not develop post-TPB infections and all the post-TPB infection isolates (urine and blood), regardless of whether the source patient underwent pre-biopsy rectal culture. Of note, not every patient had a rectal culture despite its being part of the biopsy protocol due to logistical reasons (e.g., lack of culture media).

Of the patients who underwent TPB, 15% carried fluoroquinolone-resistant rectal E. coli before biopsy. Post-TPB infection was more common in those who were colonized (13/121 [10.7%]) vs. non-colonized (8/649 [1.2%]; P < 0.001). Risk factors for post-TPB infection included hospitalization in the last year (OR, 4.5; 95% CI, 1.1-19.4; P = 0.04) and colonization with fluoroquinolone-resistant E. coli (OR, 4.55; 95% CI, 1.2-18.2; P = 0.03). Twenty percent of patients received supplemental prophylactic antibiotics in addition to ciprofloxacin, of which a single dose of intramuscular ampicillin was the most common agent prescribed (151/160; 94%). The infection rate was similar among patients who did and did not receive supplemental antibiotics (2.5% vs 2.7%, respectively; P = 0.83). Finally, the tested virulence genes did not differ significantly between the colonization and infection isolates (P = 0.73).

COMMENTARY

This study provides the first direct evidence that a patient’s own microbiota is the source for most infections following a TPB. This finding implies, but does not prove, that rectal bacteria are directly introduced into the blood, urine, and/or prostate tissue by the biopsy needle. Furthermore, the antibiotic-resistant E. coli that cause these infections can be identified prior to the procedure by a rectal culture. So what are the clinical implications of this study? It is likely premature to recommend rectal cultures for all patients for whom a TPB is planned. However, this approach is reasonable for select patients, such as those hospitalized in the past year or at high risk for having fluoroquinolone-resistant pathogens (e.g., recent fluoroquinolone use, history of a fluoroquinolone-resistant pathogen, travel to a country with a high prevalence of fluoroquinolone-resistant organisms, and immunocompromised patients at increased risk for sepsis). Another scenario could be as part of an infection control policy if the institution had an especially high rate of post-TPB infections.

The main disadvantage of rectal cultures is the additional cost. However, this must be balanced against the costs associated with TPB infections, such as emergency department visits and hospitalizations. Further cost-benefit studies are warranted to clarify this issue. Moreover, additional prospective, randomized studies are needed to determine whether choosing a pre-procedure antibiotic based on a rectal culture will lead to better outcomes while minimizing additional antibiotic usage.