The most common infectious complications in kidney transplant recipients are bacterial (64%), viral (22%) and fungal (11%). Urinary tract infection could jeopardize renal graft’s prognosis.
The objectives of this study are to know the prevalence of UTI in renal transplant recipients and the microbiological profile according to the prophylaxis strategy, and to explore if there is an association between UTI and graft’s survival.

Retrospective study of 1845 patients who underwent renal transplantation in four general hospitals. 
Patients were divided into two study groups according to the presence or absence of UTI after renal transplantation, and different subgroups were stablished depending on UTI management: 
•  Group A (patients with UTI after transplantation) 
           o	GA1 (n=324): Antibiotic (ATB) on request
           o	GA2 (n=45): ATB on request and D-mannose+ proanthocyanidins + ursolic acid
           o	GA3 (n=18): ATB on request and Trimethoprim 160mg/Sulphamethoxazole 800mg SD at night
           o	GA4 (n=63): Trimethoprim 160mg/Sulphamethoxazole 800mg SD at night
           o	GA5 (n=81): Sublingual polybacterial vaccine (Uromune)
           o	GA6 (n=864): Other treatments or prophylaxis
•  Group B (patients without UTI after transplantation). 
           o	GB1 (n=224): Antibiotic (ATB) on request when UTI is clinically suspected (not confirmed in culture or blood test).
           o	GB2 (n=18): Continuous night-time ATB prophylaxis
           o	GB3 (n=207): No prophylaxis or treatment
Variables: medical background, urine cultures (UC), UTI episodes, renal function.

Patients in GA have had more frequently pre-transplant UTIs (14.26%) than patients in GB (2.22%). Patients in GA5 were patients with a higher risk of UTI due to a higher rate of UTI in the past.

During the first year after renal transplantation:
-	75.6% of patients presented with at least one positive UC
-	28.78% of patients had ≥2 positive UC
-	24.39% of patients did not have UTI

The absolute quantification of the UC microorganisms was 90% Aerococcus urinae, 74.2% Candida species, 35.5% Escherichia coli (3.2% ESBL), 19.4% Enterococcus faecalis, 12.26% Klebsiella pneumoniae (6.45% ESBL), 10.32% Citrobacter freundii, 11.6% Enterococcus faecium, 6.45% Proteus mirabilis, 6.45% Pseudomonas aeruginosa and 6.45% Staphylococcus epidermis.

The subgroup of patients with UTI after transplantation and unknown UTI management (GA6) showed the lowest number of positive urine cultures (UC) per year (mean 1.69), and patients who received a polyvalent bacterial vaccine (GA5) showed the highest number of positive UC per year (7.3). GA1 showed a mean of 6.41 positive UC/year, GA2 5.8 positive UC/year, GA3 3.5 positive UC/year, GA4 4 positive UC/ year.

The subgroup with antibiotic plus prophylaxis (GA3) (p = 0.0000001) showed a lower number of positive results in the last UC; the subgroups with prophylaxis (GA4) and vaccine (GA5) showed a higher number. 
Higher percentage of ESBL-E.coli in those patients with ATB-based prophylaxis (10.8%) than with vaccine (GA5, 0%). GA5 patients did not show ESBL-E.coli, nor Candida.

No differences in graft's function prognosis were found between patients with or without UTI after transplantation (graft loss: 2.65% in GA, and 2.66% in GB). No significant differences in the subgroups GA neither: GA1 2.77%, GA2 2.22%, GA3 0%, GA4 2.17%, GA5 2.46%, GA6 2.66%.

It has been previously reported that UTIs did not increase risk for renal graft loss, but were associated with increased mortality after surgery (1). In the same study, the authors suggested that significant risk factors for post‐transplant UTIs were advanced age, female gender, reflux kidney disease, use of azathioprine, and cadaveric donor transplantation (1). 
The percentage of patients presenting at least one UTI in the first year after renal transplantation is greater in our study than in other similar reports (2), maybe due to the high prevalence of pre-transplantation RUTI in our sample. The spectrum of identified microorganisms is in concordance with other papers.
On the other hand, we want to highlight that, according to a recent report, the treatment of asymptomatic bacteriuria in this special population may diminished the microbiological cure and even increase the rates of microbiologic relapses and reinfections and the development of symptomatic UTIs (3). Therefore, urine culture screening is not recommended in post-transplant patients and they should only be performed in the presence of symptoms suggestive of UTI.

Pre-transplant UTI predisposes to post-transplant UTI. E. coli is less common in the group with antibiotic on request (58%) than in the group who received polybacterial vaccine (98%), but the proportion of ESBL-E. coli is higher in patients with antibiotic (10.8%) compared to the vaccine (0%).
Graft loss rate in the first year after renal transplantation is 2.6% regardless of UTI development. Differences in UTI diagnostic criteria and the influence of UTI on post-surgical morbidity instead of on complete graft loss may explain this finding.

Chuang, P., Parikh, C.R. and Langone, A. (2005), Urinary tract infections after renal transplantation: a retrospective review at two US transplant centers. Clinical Transplantation, 19: 230-235. https://doi.org/10.1111/j.1399-0012.2005.00327.x
Memikoglu KO, Keven K, Sengül S, Soypaçaci Z, Ertürk S, Erbay B. Urinary tract infections following renal transplantation: a single-center experience. Transplant Proc. 2007 Dec;39(10):3131-4. doi: 10.1016/j.transproceed.2007.10.005.
Fontserè S, Infante-Domínguez C, Suárez-Benjumea A, Suñer-Poblet M, González-Corvillo C, Martín-Gutiérrez G, Bernal G, Pachón J, Pachón-Ibáñez ME, Cordero E. Impact of Treating Asymptomatic Bacteriuria in Kidney Transplant Recipients: A Prospective Cohort Study. Antibiotics (Basel). 2021 Feb 22;10(2):218. doi: 10.3390/antibiotics10020218.