Bacterial infections of the urinary tract occur more frequently in dogs than cats. Although inflammation of the lower urinary tract is common in cats, bacterial infections are rare. Fewer than 2% of the cases of lower urinary tract inflammation (LUTI) in cats are caused by a primary urinary tract infection (UTI).
Most of the UTIs in dogs involve bacterial inflammation of the lower urinary tract (bladder, urethra); however, the ascension of bacteria into the ureters and kidneys is a potential sequela of lower UTIs. Compared with the incidence of bacterial UTIs, mycoplasmal, chlamydial, viral, and fungal UTIs are rare in dogs. Most bacterial infections of the lower urinary tract respond quickly to appropriate antibiotics treatment; however, UTIs associated with defects in the host immune system often fail to respond to antibiotic therapy, or the infection relapses shortly after antibiotic withdrawal.
Inflammation of the lower urinary tract often results in pollakiura, stranguria, and gross or microscopic hematuria. Urinalysis findings compatible with a lower UTI include bacteriuria, hematuria, pyuria, and increased numbers of transitional epithelial cells in the urine sediment. In addition, an increased urine protein concentration and alkaline urine may be observed. Cystocentesis constitutes the best way to collect urine for urinalysis and bacterial culture, because it prevents urine from being contaminated by bacteria inhabiting the distal urethra.
Urine for bacterial culture may be obtained by antepubic cystocentesis, urinary bladder catheterization, or a midstream catch during voiding. However, the number of organisms isolated in a normal dog or cat varies according to the technique used. Ideally, urine should be obtained by cystocentesis, and urine specimens should be plated within 30 minutes of collection.
If this is not possible, the urine sample should be refrigerated, because bacteria may double their numbers in urine every 45 minutes at room temperature, resulting in false-positive culture findings. On the other hand, false-negative urine culture results may be obtained if the urine has been frozen or refrigerated for 12 to 24 hours or more.
Animals with recurrent urinary tract infections (UTIs) or a UTI that does not respond to appropriate antibiotic treatment should undergo ultrasonography or contrast-enhanced radiography in a search for underlying anatomic disorders. Bladder tumors or polyps, uroliths, pyelonephritis, prostatitis, and urachal remnants are common causes of recurrent or unresponsive UTIs. In some cases, systemic disorders such as hyperadrenocorticism, chronic renal insuffiency-failure, and diabetes mellitus may be associated with recurrent UTIs, as can long-term corticosteroid treatment.
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