Do cats get bacterial urinary tract infections (Proceedings)
Prevalence and Risk Factors
The normal feline lower urinary tract has a number of defence mechanisms against infection. These include normal micturition (e.g., frequent and complete voiding), normal anatomy (e.g., length of urethra), uroepithelial mucosal barriers, the antimicrobial properties of normal urine (e.g., high specific gravity and osmolality) and a normal immune system.1 The lower urogenital tract and the rectal area have a resident population of normal flora, a ready source of pathogens for ascending infections.
Bacterial infections may affect both the upper and lower urinary tract of cats. Information on the incidence of bacterial lower urinary tract disease (LUTD) varies with the population of cats studied. Prospective studies of young cats with LUTD identified bacterial urinary tract infections (UTI) in less than 2% of cases.2-3 However, higher rates of UTI in cats with LUTD have been documented, although the data reported is often not stratified by age. In one study of 134 cats in Norway with LUTD identified 33% with UTI.4 Analysis of over 22,000 cats with LUTD in the Purdue Veterinary Medical Database from 1980-97 found 12% were diagnosed with UTI.5 In a study of 77 cats in Switzerland with LUTD, 8% were diagnosed with UTI.6 In a UK study of 434 cat with LUTD signs, 22% had confirmed bacteriuria.7 Bacterial UTI can also occur in cats without clinical signs of LUTD. A study of 132 urine specimens from cats without signs of LUTD found 29% with bacterial infection.8 Older female cats were at highest risk. Some of the differences in study results may be due to differences between cats seen as first-opinion cases versus those seen as referral cases.Persian cats, female cats, increasing age and decreasing body weight are typically found to be risk factors for UTI.5,9-11 Factors such as urethral catheterization and perineal urethrostomy12 also increase the risk of bacterial UTI. Bacterial UTI can develop in healthy male cats with indwelling urinary catheters; risk of infection increases with duration of catheterization.1 The risk of infection also increases with open indwelling systems, corticosteroid administration, diuresis and pre-existing urinary tract disease. The practice of administering antimicrobials while an indwelling urinary catheter is in place is tempting, but should be discouraged as it may promote the development of multi-drug resistant infections.1
UTI is an important problem of older cats (>10 years).5 It is assumed that the decline in immune competence with aging is responsible in part, as well as the increased prevalence of concurrent diseases in this age group. Cats with certain diseases are at increased risk of bacterial UTI, particularly hyperthyroidism (HT; 12-22%), diabetes mellitus (DM; 10-13%) and chronic kidney disease (CKD; 13-22%).9-11,13-14 Interestingly, decreasing urine specific gravity was not associated with a positive urine culture in cats with CKD, DM and HT.11 Other predisposing factors may be responsible for the increased risk of UTI in these patients.
Clinical signs and Diagnosis
Cats with infections of the lower urinary tract have typical non-specific signs of LUTD, including pollakiuria, dysuria, stranguria, hematuria and inappropriate urination (periuria). However, asymptomatic infections are also possible.13-14 Differential diagnosis includes other lower urinary tract diseases, such as idiopathic cystitis, urolithiasis, neoplasia and behavioural disorders. A full urinalysis (urine specific gravity, urine chemistries, and microscopic sediment examination) should be performed on all cats with signs of LUTD, and should be part of the routine minimum database for older cats or ill cats. Changes on urinalysis consistently associated with bacterial UTI include bacteriuria, pyuria (>5 white blood cells/HPF) and hematuria. Proteinuria may also be present. However, there may be no changes on urinalysis or routine laboratory data to indicate UTI.13 Proper interpretation of urinalysis samples takes into account changes induced by collection method and other factors.15 It is important to evaluate urine samples within 60 minutes of collection. Storage for longer periods of time, especially with refrigeration, may cause in vitro formation of struvite or calcium oxalate crystals.16-17 Urine pH and specific gravity are generally not affected by storage. In vitro formation of struvite crystals is especially a risk in stored urine samples from cats fed dry food diets.17
Urine culture and sensitivity testing is recommended for cats at increased risk of UTI due to concurrent disease or with recurrent episodes of lower urinary tract signs. Samples for culture should be collected before any therapy is initiated and preferably are collected via cystocentesis.18 Urine samples for culture should be processed as soon as possible. If processing will be delayed for more than 30 minutes, the sample should be refrigerated in a sterile container. The sample may be stored in this way for 6-12 hours without additional bacterial growth.19 Commercially available urine culture collection tubes containing preservative may be used to refrigerate urine specimens for up to 72 hours.20 The most commonly isolated organism is E. coli.9,13-14,21 Other organisms that have been isolated include Staphylococcus spp., Streptococcus spp., Enterococcus spp., Klebsiella spp. and Enterobacter spp. Corynebacterium spp. have been identified as a cause of UTI in cats with pre-existing lower urinary tract abnormalities and a history of previous UTI with other organisms.22-24