Update on Diagnosis and Management of Urinary Tract Infections in Dogs and Cats

By Tara Ghormley, DVM, DACVIM

Urinary tract infections (UTIs) are among the most common reasons for veterinary visits but their management requires careful consideration. Overuse and misuse of antimicrobials can contribute to resistance, making treatment less effective over time. To address this, the International Society for Companion Animal Infectious Diseases (ISCAID) developed updated guidelines in 2019 to standardize diagnosis and therapy.

What Counts as a UTI?

A urinary tract infection is defined as the adherence, multiplication, and persistence of an infectious agent within the urogenital system, producing an inflammatory response and clinical signs.

• UTIs are far more common in dogs than cats.

• Only about 1–2% of cats will develop one in their lifetime, though prevalence rises with age.

• Most infections are caused by a single bacterial species, typically E. coli.

• Other potential pathogens include Streptococcus, Klebsiella, Proteus, and Staphylococcus.

• Enterococcus is frequently found in subclinical bacteriuria and is often multidrug resistant .

Sporadic Bacterial Cystitis

Also called uncomplicated UTIs, these occur in otherwise healthy patients with normal urinary tract anatomy. They are defined as fewer than 3 episodes in a 12-month period.

Key points:

• Clinical signs such as pollakiuria, stranguria, dysuria, and hematuria must be present to diagnose an infection.

• In cats, most patients with these signs do not have bacterial cystitis—instead, they often suffer from idiopathic (sterile) cystitis.

• Urinalysis is required in all cases, but pyuria alone is not diagnostic.

• Urine culture should always be performed, especially in cats, to confirm infection. Aerobic culture after cystocentesis is the gold standard.

Treatment:

• Use NSAIDs (unless contraindicated) to manage discomfort while awaiting culture.

• Avoid immediate empirical antibiotics in cats unless culture confirms infection.

• Amoxicillin is usually the first-line treatment, with trimethoprim-sulfa as an alternative in dogs.

• Duration: 3–5 days.

• Avoid fluoroquinolones, nitrofurantoin, and third-generation cephalosporins unless resistance to first-line options is documented.

• Bladder infusions and post-treatment cultures are not recommended.

Recurrent Bacterial Cystitis

Recurrent infections are defined as ≥3 UTIs in a year or ≥2 in six months. These may be:

• Reinfections wherein different organisms are found each time.

• Relapses when the same organism is found in each infection.

Underlying factors are common in these patients including: endocrinopathies (Cushing’s, diabetes), obesity, renal disease, vulvar or urinary tract conformational defects, uroliths, prostatic disease, bladder tumors, or immunosuppressive therapy.

Management approach:

• Always perform a culture.

• Imaging (ultrasound, radiographs, contrast studies, or cystoscopy) may be needed for refractory cases to look for underlying pathology.

• Use NSAIDs for comfort while awaiting results.

• Reinfections: short courses of antibiotics still indicated (3–5 days).

• Relapses: longer antibiotic course can be considered (7–14 days).

• Do not use prophylactic antibiotics.

• Focus treatment on clinical cure, not sterile urine.

Subclinical Bacteriuria

Subclinical bacteriuria means bacteria are present in the urine without clinical signs.

• Common in older dogs, diabetics, obese patients, and those on immunosuppressants.

• More frequent in female dogs and rare in cats.

• Most cases do not require treatment.

Treatment is only indicated in:

• Suspected pyelonephritis.

• Before urinary tract surgery.

• In unregulated diabetics or those with diabetic ketoacidosis.

• With struvite urolithiasis.

Even in these cases, evidence supporting treatment is limited. Routine urine culture in CKD or diabetic patients is not recommended.

Pyelonephritis

Pyelonephritis involves infection of the renal pelvis and parenchyma, usually due to ascending infection from the bladder.

• E. coli is the most common culprit.

• Signs include fever, lethargy, PU/PD, renal pain, azotemia, and inflammatory leukogram.

• Definitive diagnosis requires renal culture or biopsy, but repeated cystocentesis and culture, combined with clinical signs, is often used in practice.

Treatment:

• Start antibiotics immediately, preferably fluoroquinolones or cefpodoxime, as they penetrate renal tissue.

• Tailor therapy once culture results are available.

• Typical duration of treatment is 10–14 days.

• Always recheck a positive culture 1–2 weeks after completing therapy.

Bacterial Prostatitis

Seen primarily in intact male dogs, prostatitis is caused by bacteria such as E. coli, Klebsiella, Staphylococcus, and Brucella canis.

Diagnosis requires ultrasound and urine culture, with prostatic aspirates or biopsy for confirmation in some cases. Because the blood–prostate barrier limits drug penetration, many antibiotics are ineffective.

Treatment principles:

• Castration is recommended for non-breeding dogs.

• Abscesses should be drained surgically or via ultrasound guidance.

• Fluoroquinolones penetrate prostatic tissue best and are good empiric choices.

• Trimethoprim-sulfa may also be used.

• Treatment duration is 4-12 weeks.

Additional Clinical Notes

• Catheter-associated bacteriuria: Do not use prophylactic antibiotics. Culture only if clinical signs of dysuria persist after removal.

• Chronic kidney disease patients: Culture only if clinical signs of UTI are present or pyelonephritis is suspected. Subclinical Enterococcus infections should not be treated.

• Critical antibiotics: Reserve vancomycin, carbapenems, and third-/fourth-gen cephalosporins for proven multidrug-resistant infections. Never use them for subclinical bacteriuria.

Key Takeaways

• Clinical signs are required for diagnosis—bacteriuria alone is not a UTI.

• Subclinical bacteriuria is common, especially in older patients, but usually should not be treated.

• Recurrent infections warrant investigation for underlying disease, not just repeated antibiotics.

• Short antibiotic treatment durations (3–5 days) are effective for uncomplicated cases.

• Antimicrobial stewardship is critical—save broad-spectrum and critically important antibiotics for resistant, complicated infections only.