This is the first report attempting to evaluate the risk factors of positive intraoperative and postoperative urine culture in cats after SUB device placement for the treatment of feline ureteral obstructions. The present study identified 35.7% of new positive urine culture during the follow-up period. Overall, 15.6% of chronic UTI were identified in this cat population. Cats with a decreased BCS and a longer hospitalization duration had significantly increased risk for the development of positive urine culture after hospital discharge. However, positive intraoperative urine cultures were not related to the development of signs consistent with UTI during the follow-up period, and duration of surgery and anesthesia were not associated with positive urine bacterial cultures.
The use of a SUB device was recently reported in a large series of 134 cats with good outcomes [1]. Three studies reported that cats treated with SUB device had a 88 to 94% survival to discharge rate [1, 9] and a 1 year survival of 83% [7]. In the present study, survival to discharge rate was 100%. Three cats died during the follow-up period, at 262, 448 and 1231 days.
In previous studies, postoperative positive urine culture, obtained from the SUB port, was reported from 21 to 25% of the cases [1, 6, 7]. Our findings were slightly higher compared to those reported as we identified 35.7% of positive bacterial urine culture during follow-ups. All of the urine samples were obtained from the SUB port in order to avoid contamination. Bacteriuria resolved in 60% of the cases with appropriate antibiotic treatment which is consistent with the previously reported data of 50 to 78% of cats [1, 2].
As recommended by Kopecny et al. [6] a distinction between subclinical bacteriuria and UTI was made to determine the clinical relevance of infection and the necessity to administer antibiotics. This distinction allowed us to identify chronic UTI in 15.6% of cats which is much higher than the 8% previously reported in a study of 132 cats [1]. In our study, 3.1% of cats had subclinical bacteriuria, which is consistent with the 4.9% previously reported [1] but lower than the 12.5% reported in another study [6].
The effectiveness of extending post-operative antibiotic treatment could not be determined within the limits of this study. It appears in a study that post-operative antibiotic treatment administration decreased the risk for development of positive urine culture after discharge, with a median duration of 5 days of treatment [6]. In the present study all cats received prophylactic antibiotic treatment for 7 days until reception of bacterial culture results. The antibiotic treatment was stopped if the urine culture was negative and pursued for 3 weeks if positive, with the antibiotic based on sensitivity [10, 11]. Antibiotic use following surgery may be associated with a decrease of bacterial colonization of the SUB device [6].
The most commonly isolated pathogens were E coli, E faecalis and P aeruginosa. This is consistent with other studies reporting SUB placement but also with cats with bacteriuria diagnosed by urine culture where E coli and Enterococcus species are the most common feline urine pathogen cultured [1, 6, 12,13,14,15]. Enterococcus species was significantly more common in cats with subclinical bacteriuria [12, 15], this was however not the case in another study with ureteral devices [6]. These characteristics could lead to an absence of antimicrobial treatment depending on the clinician. However, Enterococcus spp. has an ability to form biofilms [13] and implant surfaces act as substrates for bacterial biofilm formation [16], which will be recalcitrant to antibiotic therapy. E faecalis was isolated in 2 urine culture in our study and both cats were treated with appropriate antibiotic treatment which led to a resolution of their clinical signs. A left subcapsular perirenal abscess combined with a severe pyelonephritis was diagnosed 3.5 years following initial surgery in a cat with subclinical bacteriuria (E faecalis and E coli). The ability of Enterococcus spp. to form biofilms associated with a decrease of host immune response could have led to the development of the abscess. However, the bacterial strain responsible for the perirenal abscess was not identified as no bacterial culture was performed since the cat died during the nephrectomy. Although causative bacteria is unknown, this long-term complication has never been described before and emphasizes the interrogation to treat subclinical bacteriuria.
Berent et al. (2018) found that cats with a positive urine bacterial culture result or bacteriuria during surgery of SUB device placement were significantly more likely to have bacteriuria at some time after surgery and to have persistent UTI. In the present study, these findings were not observed. However, our results come from a small number of cats and should therefore be interpreted with caution.
Of the 32 cats included, the SUB device type was compared with positive bacterial urine culture and no significant predilection were found. However, this absence of significant difference between the groups in our study may reflect a type II error. The 3-way port allows to connect both kidneys to a single bladder catheter for bilateral ureteral obstructions. It is ideal for bilateral ureteral obstructions in compromised patients because it reduces the anesthesia duration [8]. Risk factors for infection and mineralization of this type of device have not been evaluated and compared to single port device, but there are theoretically more potential risks from using this device as a mineralization or a kink of the bladder catheter negatively impact both kidneys. More recently, new port design with a larger chamber of silicone were marketed. This design is supposed to create more turbulence during flushing procedure. Further studies evaluating the 3-way port and this new chamber design are warranted. Additionally, the therapeutic use of tetrasodium ethylenediaminetetraacetic acid solution (tEDTA) has been evaluated during SUB flushing to prevent and treat biofilm infection and to prevent and treat mineralization occlusion [1]. tEDTA is effective at eradicating biofilms formed by microorganisms from central venous catheters in human patients [1, 17]. In a recent study, the implementation of routine irrigation of the SUB device using 2% tEDTA led to a decrease in both infection and mineralization rate associated with SUB devices. In 8 SUB device occlusions secondary to mineralization, obstruction resolved after treatment with tEDTA infusion [18].
There was a significant difference in hospitalization duration between positive and negative bacterial urine culture group (5 days versus 6 days, P = 0.022). The use of indwelling urethral catheter after SUB device placement to quantify urine output is associated with positive postoperative urine bacterial culture results in 2 studies [1, 14]. However, in our institution, use of non-absorbent cat litter improve the ability to accurately quantify urine output, which explain that no cats in this study had an indwelling urethral catheter.
Evaluation of health-care associated infection, which are infections animals get while they receive health-care for another condition, in critical care units of small animal referral hospitals found that 12% of cats have had one or more nosocomial infection occur during hospitalization [19]. One of the risk factors found to have a positive association with development of a nosocomial infection was longer hospital stay [19]. However, median time from discharge to identification of the first positive urine culture was 159 days (range 8–703) in this study. If the bacteriuria was caused by a contamination during hospitalization, it should have been diagnosed in the first few days after discharge. Pathogen isolated were mostly E coli and E faecalis. These organisms are known to form bacterial biofilms and to grow more slowly than planktonic state bacteria [20, 21]. While 68% of ureteral stent in human patients become colonized in one study, only 27% of bacteriuria was documented [22]. Therefore, a negative urine culture does not rule the possibility of SUB device colonization. Interestingly, if antimicrobial susceptibility testing is based on bacterial culture derived from planktonic bacteria, antimicrobial agent might be ineffective against bacteria in biofilm which differ in behaviour and in phenotypic form from planktonic bacteria [21].
There was also a significant difference in body condition score between urine culture-negative and urine culture-positive groups (5/9 versus 4/9, P = 0.03) which is consistent with the risk factors evaluation for development of UTI in cats [14]. A risk factor that was also identified with increased odds of UTI was a decreased BCS. It may be explained by the advanced status of concurrent conditions predisposing to UTI via patient debilitation, weakened immune system and increased susceptibility to infection [14].
No significant differences were identified between urine culture-negative and urine culture-positive groups concerning the progression of chronic kidney disease. This is consistent with a previous study in cats with hyperthyroidism, diabetes mellitus and chronic kidney disease which reported no association between UTI and increased serum creatinine concentrations [23]. In another study, the presence of clinically relevant chronic kidney disease (IRIS stage 2–3) was not identified as a risk factor for the development of a positive urine culture and UTI occurred independently of concurrent chronic kidney disease [6].
This study has a number of limitations, related to its retrospective nature. A small number of cats met the inclusion criteria. The small group sizes may have limited the power, and hence differences in studied parameters, such as the surgery or anesthesia duration, SUB device type and the progression of the chronic kidney disease, may have reached statistical significance in a larger population. Therefore, this absence of significant difference between the groups in our study may reflect a type II error. The duration of antimicrobial treatment was standardized between the animals in this study, but remains dependent on the wishes of each institution. Selection bias is possible because urine culture may have been performed in cats with clinical signs compatible with UTI. Asymptomatic bacteriuria might have been missed with only a urinalysis. Further studies evaluating the effect of post-operative antimicrobial administration in a larger group of cats with SUB device placement are necessary.
