Urinary tract infection

Owners usually notice straining to urinate, frequent passing of small amounts, urination in the house, blood in the urine, strong-smelling urine and licking at the genitals. Pyelonephritis may bring fever and kidney pain, although vague signs such as poor appetite and lethargy are more typical. Many older cats with bacteria in their urine show no signs at all. Urinalysis shows white cells, red cells and bacteria in the sediment.

A urinary tract infection develops when bacteria from outside the body enter the bladder, get past the urinary tract's defences and establish infection. In health those defences are frequent voiding, normal resident flora, an intact anatomy and the antimicrobial properties of urine. Escherichia coli is the commonest cause in both dogs and cats; uropathogenic strains use virulence factors such as P fimbriae to attach to, invade and persist in the tissue. In cats, Enterococcus faecalis, Staphylococcus felis and streptococci follow, and most infections involve a single organism. Infection may stay in the bladder (bacterial cystitis) or ascend to the kidney (pyelonephritis). Bacteria can also be present in urine without disease, which is termed subclinical bacteriuria.

Dogs and cats are both affected. In cats, infection is uncommon overall, affecting only 1-2% in their lifetime, but among cats over ten presented with lower urinary tract signs, 40-45% have one. Female cats and cats with chronic kidney disease, diabetes mellitus or hyperthyroidism are at higher risk, as are cats with a perineal urethrostomy or an indwelling urinary catheter. In dogs, predisposing conditions include bladder stones, incontinence, diabetes, Cushing's disease, intervertebral disc disease, anatomical abnormalities, immunosuppressive drugs, kidney disease and cancer. Recurrence is defined as two or more infections in six months or three or more in a year in dogs, and typically more than three episodes in twelve months in cats.

In cats, feline idiopathic cystitis produces the same frequent, painful, bloody urination but yields no significant growth on culture. Urolithiasis and bladder neoplasia also cause lower urinary tract signs and are identified by imaging. Subclinical bacteriuria is separated by the absence of clinical signs. Confirmation of infection needs a cystocentesis sample with growth of at least 1,000 colony-forming units per millilitre on quantitative culture.

Urinary bladder, kidneys (pyelonephritis), lower urinary tract, urine

No preventive measure is formally recommended; cranberry extract, probiotics and low-dose antimicrobial prophylaxis rest on anecdotal evidence. Identify and manage predisposing conditions, and do not treat bacteriuria in animals without signs.

Good: most uncomplicated cases resolve quickly on culture-guided antibiotics. Recurrent cases hinge on susceptibility and control of the underlying disease. Untreated subclinical bacteriuria did not shorten survival in older cats.