Diagnosis and Management of Initial and Recurrent Urinary Tract Infections

Bacterial urinary tract infection (UTI) occurs in approximately 14% of dogs in their lifetime, with a variable age of onset. Animals with a UTI can present with stranguria, pollakiuria, dysuria and urinary incontinence, although some animals may have no clinical signs. Spayed female dogs are at increased risk for a UTI, which is likely due to anatomic differences as well as possible protective secretions from the prostate in sexually-intact males. Urinary tract infection (UTI) occurs when bacteria colonize portions of the urinary tract that are normally sterile (i.e., kidney, ureter, bladder, and proximal urethra).Ascent of bacteria is the most common origin of bacteria in UTI. Fecal flora from the patient contaminate the perineum, ascend the urethra, and enter the bladder. Organisms that successfully gain entry into the bladder then have the potential to ascend the ureters, cross the renal pelvic epithelium, and enter renal parenchymal tissue. Vaginal, preputial, and distal urethral flora occasionally are the source of ascending bacteria. Ascending organisms can also come from the environment including that from hospital flora. Introduction of normal flora during catheterization and contamination with fecal or hospital flora also is possible. Migration of bacteria around an indwelling urinary catheter or through the catheter lumen occurs at times. The urinary tract is exquisitely resistant to bacterial colonization during health. UTI results from abrogation of one or more natural defense mechanisms that allow bacteria to ascend from the perineum to the urethra, and then to the bladder The development of a UTI means that the host defenses were overwhelmed at least transiently in order for UTI to develop. In order for UTI to develop, the animal must be exposed to to uropathogenic bacteria in sufficient numbers, the animal must have epithelial receptors for uropathogens, and often suboptimal urinary defenses exist. Failure of normal urinary defenses include the possibilities of reduced anti-adherence properties of the uroepithelium, decreased antibacterial properties of urine, abnormal patterns of voiding, reduced integrity of intrinsic mucosal defenses, and presence of anatomic abnormalities. Increased risk for the development of UTI occurs in dogs with anatomic abnormalities of the genitourinary system such as urachal remnants, ectopic ureters, excessive perivulvar skin folds/pyoderma (especially in recurrent UTI), or possisbly vestibulovaginal stenosis. Exogenous steroid use in dogs, endogenous hyperadrenocorticism, and diabetes mellitus all add risk for development of UTI in dogs. Uroltihiasis can be the result of UTI (struvite stones in dogs) or the stones may compromise the urinary defense systems. Urethrostomy, indwelling urinary catheterization, and single passage of a urinary catheter increase the risk that UTI will be acquired in dogs and cats. UTI occurs in approximately 30% of all cats with chronic renal failure (CRF), many within one year of diagnosis of CRF. Cats over 10 years of age that present for signs of lower urinary tract distress (LUTD) commonly have bacterial urinary infections, unlike young cats presenting with LUTD signs. Dogs with urinary incontinence may be at increased risk for development of UTI possibly due to the “wicking” action of urine that may allow ascent of bacterial organisms.