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Urine cultures in cats with subcutaneous ureteral bypass systems

Pennington CE, Halfacree Z, Colville-Hyde C, Geddes RF. Factors associated with positive urine cultures in cats with subcutaneous ureteral bypass system implantation. J Feline Med Surg [Internet]. 2020 Aug 25.

Obstruction of feline ureters due to stricture, stones, neoplasia, infection, or other causes is often treated with the placement of a subcutaneous ureteral bypass (SUB) device. These systems allow urine to flow from the kidney to the bladder, avoiding the ureter, and with a subcutaneous port to allow flushing and collection of urine samples. While these devices have improved the longevity and quality of life in cats with ureteral obstruction, recurrent urinary tract/SUB infections are common after implantation. These may require multiple interventions to treat, especially if drug resistant biofilms form.  Understanding how infections occur and what factors predispose to them is essential to their prevention and treatment.

The objectives of this study were to report the incidence of SUB associated bacteriuria and risk factors in a large population of UK cats; to identify the commonly implicated bacterial isolates; and to determine if there is a correlation between post-surgical culture and the need for further intervention.

The study was designed as a retrospective observational trial investigating cats presenting to the Queen Mother Hospital for Animals from 2011 to 2019 who had a SUB implanted. Cats were included if they survived to hospital discharge and had at least one post discharge urine culture. Diagnosis of ureteral obstruction was done routinely, with SUB implantation as per manufacturer recommendations. Cats with an active urine sediment were treated with antibiotics for 48 hours pre-operatively (if possible) and 4-6 weeks postoperatively. Urine samples were collected from the SUB port 1 month postoperatively, then ever 3 months for a year, then every 6 months. From February 2019, flushes were done with TetraEDTA.

One hundred twenty-four cats had a SUB implanted, of which 118 met inclusion criteria. Median age was 7.17 years, 59% were spayed females and 39% neutered males. In 79% of cases a SUB was placed due to ureterolithiasis, in 3.4% iatrogenic injury, 0.8% ureteral stricture, and 17% no cause was identified.

39% of cats had unilateral SUBs placed, and 61% bilateral. Cats were hospitalized a median of 6 days.

One hundred ten cats had a preoperative urine culture performed, of which 12.7% were positive. The most frequent isolates were Escherichia coliand Enterococcus fecalis. Six of these cats had a positive postoperative culture, four of which had the same isolate.

All cats had at least 1-month follow-up. Of these, 8.5% had a positive urine culture with the most common isolates being E coli and Pseudomonas aeruginosa. 13.4% of cats had a positive culture within 3 months of surgery, 26.3% within 6 months, and 41.2% within one year.

Cats with a positive pre-operative culture were significantly more likely to have a positive post-operative culture within 6 months of surgery. Cats with higher end-anesthetic rectal temperatures were less likely to return a positive culture within 1 or 3 months post-surgery.

Age, sex, breed, weight, body condition score, perioperative antibiotic choice, reason for device placement, outdoor access, preoperative urea, creatinine, urine pH and specific gravity, and length of hospitalization, anesthetic and surgery, use of TetraEDTA, sex, and site of implantation were not significantly associated with a positive urine culture at any time point.

36% of cats with positive culture had no clinical signs, 7% had asymptomatic device obstruction, 39% had lower urinary tract signs or pyelonephritis, and 18% had transient lower urinary signs.

Eleven cats with a positive culture had their device removed or replaced. There was no correlation between device removal and clinical signs.

Cats culturing positive for E. coli were significantly more likely to have their device removed or replaced, while cats culturing pseudomonas post operatively were more likely to have device occlusion.

The authors conclude that postoperative bacteriuria occurred at least once within 12 months postoperatively in 23.7% of cats and was a risk factor for device removal or replacement. Perioperative hypothermia and postoperative positive culture were predictive of postoperative culture positivity.

While this study was limited by its retrospective design, it had a reasonably large population of cats with thorough workup. It serves as a valuable resource to attempt to reduce the risk of SUB infection and obstruction. (MRK)

See also:

Berent A, Weisse C, Bagley D, et al. Use of a subcutaneous ureteral bypass device for treatment of benign ureteral obstruction in cats: 174 ureters in 134 cats (2009–2015). J Am Vet Med Assoc 2018; 253: 1309–1327.

Deroy C, Rossetti D, Ragetly G, et al. Comparison between double-pigtail ureteral stents and ureteral bypass devices for treatment of ureterolithiasis in cats. J Am Vet Med Assoc 2017; 251: 429–437.