Effects of the use of silver-coated urinary catheters on the incidence of catheter-associated bacteriuria and urinary tract infection in dogs

OBJECTIVE To determine the effects of silver-coated versus standard silicone urinary catheters on the incidence of catheter-associated bacteriuria (CAB) and catheter-associated urinary tract infection (CAUTI) in dogs. DESIGN Randomized controlled clinical trial. ANIMALS 36 dogs requiring urinary bladder catheterization for ≥ 24 hours. PROCEDURES Dogs were randomly assigned to receive a silver-coated or non–silver-coated (control) silicone Foley catheter. Urine samples for cytologic examination and bacterial culture were collected at the time of catheter insertion and daily until catheters were removed (≥ 24 hours to 7 days later). Results were compared between groups. RESULTS No significant differences were identified between catheter groups in the incidence of CAB or CAUTI. Although the median time to development of cytologically detected bacteriuria, culture-detected bacteriuria, and CAUTI did not differ significantly between groups, median time to CAB development (either method) was significantly longer for dogs that received a control catheter rather than a silver-coated catheter. For both types of catheters combined, older age was a significant predictor of culture-detected bacteriuria, and longer duration of catheterization was a significant predictor of culture-detected bacteriuria and overall CAB. CONCLUSIONS AND CLINICAL RELEVANCE Silver-coated urinary catheters provided no clinical benefit over standard urinary catheters for the dogs of this study and were associated with earlier development of CAB but not CAUTI. A larger prospective study is required to definitively determine whether the use of silver-coated urinary catheters should or should not be considered to reduce the risk of CAB or CAUTI in dogs. Urinary catheterization is indicated for various medical conditions in veterinary species. Urinary catheters may increase the risk of bacterial contamination and colonization of the lower urinary tract via contamination of the urine collection system, allowing bacteria to gain access to the urinary tract through the catheter lumen or via catheter contact with the patient's perineal tissues, resulting in bacteria migrating along the outer surface of the catheter or within the mucous layer of the urethra.1 In dogs specifically, urinary catheterization has been significantly associated with hospital-acquired UTIs or bacteriuria.2,a In a veterinary referral hospital intensive care unit, the overall frequency of CAUTI development in dogs was reportedly 19% (26/137) but increased to 79% (11/14) for those that remained catheterized for 72 hours.3 In another study,4 the incidence of CAUTI development was 10% (4/39), and the probability of remaining UTI free by 4 days of catheterization was 63%. However, no attempt was made to distinguish bacteriuria from UTI in those studies. Various strategies have been used in human medicine to reduce the incidence of CAUTI, including improvements in catheter care, maintenance of closed urine collection systems, and addition of antibacterial coatings to catheter surfaces.5,6 Silver has antibacterial properties, and meta-analyses7 and systematic reviews8,9 comparing silver-coated urinary catheters with standard urinary catheters have revealed a beneficial effect of silver alloy in reducing the incidence of CAB in humans. An in vitro study10 showed that silver-coated silicone urinary catheters had significantly less adherent canine urinary Escherichia coli at 24, 48, and 72 hours of placement in a bacterial broth and subjectively less biofilm formation than non–silver-coated urinary catheters. We are unaware of any reported studies in which silver-coated urinary catheters have been evaluated in dogs. The purpose of the study reported here was to determine the effects of a silver-coated versus non–silver-coated silicone urinary catheter on the incidence of CAB and CAUTI in dogs requiring urinary bladder catheterization for ≥ 24 hours.