Recurrent urinary tract infections (UTI) are a common problem in dogs.1 There are 2 major types of UTI recurrence: relapse and reinfection. The implications of relapse versus reinfection are important
for diagnosis and management of recurrent UTI. Relapses are defined as UTI recurrence of the same species and serologic strain
of microorganisms within several weeks of withdrawal of therapy. Reinfections are recurrent infections caused microorganisms
that are different than the prior UTI. In addition to recurrent infections, super-infections and persistent infections are
also common issues. Super-infections are infections with resistant organisms that are acquired during treatment of an initial
UTI. Persistent infections are when the same organism does not resolve during treatment of UTI.
Causes of recurrent UTI
Common causes of UTI relapse include inappropriate antibiotic use (incorrect dose or duration, poor owner compliance), failure
to eliminate predisposing causes (uroliths, neoplasia), deep-seated infections that are inaccessible to the antibiotic (pyelonephritis,
prostatitis), and emergence of drug-resistant pathogens. Common causes of apparent reinfection include failure to eliminate
predisposing causes for UTI (e.g., perivulvar hooding and perivulvar dermatitis), systemic illness (e.g., diabetes mellitus
and hyperadrenocorticism), presence of multiple pathogens in which only sensitive pathogens were eliminated by therapy, and
Most UTIs occur from ascending bacterial infection. There are normal host defenses that protect the urinary tract from infection.
Normal voiding washes bacteria out of the urinary tract before they can establish an infection. Normal canine and feline urine
is bactericidal from high osmolality and extremes in pH (< 6.0). Urothelium has also intrinsic antibacterial properties. Mechanical
factors including the urethral high pressure zone, length of urethra, ureteral peristalsis, and ureterovesical "flap valves"
act as mechanical barriers to ascending UTI.
Interference with normal host defenses may contribute to repeated ascending infections. Common contributing factors include
incomplete voiding, urine stasis or reflux, disruption of or damage to the urothelium, alterations in immune competence, alterations
of urine composition (dilute urine, glucosuria), or iatrogenic causes (perineal urethrostomy, indwelling urinary catheters).
Young adult cats rarely have bacterial UTI unless prior procedures predispose them to acquired UTI, older cats are more commonly
affected by UTI because of concurrent diseases that cause dilute urine and or impair immune competence.
Diagnostic approach for animals with recurrent UTI
The standard diagnostic evaluation for dogs with recurrent UTI should include CBC, serum biochemistry profile, urinalysis,
urine culture, abdominal radiographs and ultrasound. The history should be reviewed for diseases or drugs that could contribute
to immunosuppression. Physical examination should include careful examination of the vulva and peri-vulvar skin for evidence
of recessed or "hooded" vulva with perivulvar dermatitis that may contribute to reinfection of the urinary tract. Subtle abnormalities
of the perivulvar region is easily overlooked during routine physical examination and should be carefully evaluated in dogs
with recurrent UTI. Rectal examination should also be included as a standard part of the physical examination to evaluate
the urethra for masses or uroliths that could contribute to recurrent UTI.
Testing for hyperadrenocorticism should be performed if there is any data that might support the presence of hyperadrenocorticism.
If available, cystoscopy is recommended for diagnostic evaluation for dogs with recurrent UTI if an underlying cause has not
been identified during initial work-up. Cystoscopy helps rule out anatomic abnormalities, polyps, neoplasia or uroliths and
permits mucosal biopsy for culture, cytology and histopathology.
Cultures of tissue or uroliths are more sensitive than routine urine culture for detecting chronic UTI especially in dogs
previously treated with antibiotics. Bacteria were isolated from bladder mucosal cultures or urolith cultures in 18 to 24%
of dogs despite concurrent negative urine cultures. While these studies utilized bladder mucosal samples from cystotomy, we
have also been able to identify bacterial and mycoplasmal UTI from cultures of mucosal biopsies obtained via cystoscopy from
dogs despite concurrent negative urine cultures.