*Purpose: Bariatric surgery (BS) is a highly effective weight loss strategy that is increasingly common, but can be associated with impaired drug absorption and alterations of the natural barrier defenses of the stomach. The risk of intra-abdominal infection and UTI has been shown to be increased after bariatric surgery in the general population, particularly in women. The impact of pre-transplant (pre-TXP) BS on infectious outcomes in kidney transplant recipients (KTRs) has not been elucidated. The primary objective of this study was to identify the risk of bacterial, fungal and viral infections (CMV, BK) in KTRs with pre-TXP BS. The secondary objective was to evaluate transplant outcomes including graft and patient survival.

*Methods: Adult patients were included if they received a kidney transplant alone between 1/1/2000-12/31/2016. The presence of pre-TXP BS was defined as Roux-en Y gastric bypass or gastrectomy via sleeve or banding procedure. Patients without pre-TXP BS were selected as controls via frequency for BMI at time of transplant, age, cause of end-stage renal disease (ESRD), and calendar year.

*Results: 69 KTRs met inclusion criteria and were matched with 1067 controls. Demographics were similar between groups with the exception of gender (male 35% in BS vs. 68% in control, p<0.001) and race (nonwhite 9% in BS vs. 20% in control, p=0.02). Recipients who had undergone pre-TXP BS had higher incidence of fungal infection (14% vs. 6%; HR 2.29, 95% CI 1.18-4.42, p=0.01), but decreased incidence of BK viremia (1% vs. 11%; HR 0.13, 95% CI 0.02-0.84, p=0.03). There was no difference in the incidence of bacterial infections (28% vs. 25%; HR=1.08, 95% CI 0.66-1.77, p=0.75). The association of BS with fungal infections was somewhat attenuated after adjustment for potential confounders (HR 1.81, 95% CI 0.93-3.52, p=0.08), but the association of BS with BK viremia was unchanged (HR 0.13, 95% CI 0.02-0.87, p=0.04). Pre-TXP BS was not significantly associated with incidence of death (HR 1.24, 95% CI 0.98-2.28, p=0.30). However, there was a trend toward higher incidence of graft loss in the BS group (HR 1.50, 95% CI 0.98-2.28, p=0.06).

*Conclusions: Pre-TXP BS does not appear to significantly impact the risk of bacterial infection after kidney transplant. There was an increased incidence of fungal infections, although this was not significant after adjustment. Interestingly, pre-TXP BS was associated with a lower incidence of BK viremia. BK is associated with the degree of iatrogenic immunosuppression (IS); patients with pre-TXP BS may have been relatively less immunosuppressed than controls, suggesting possible alterations in IS absorption. This theory may be strengthened by the trend of increased graft loss in this group, if the graft loss is due to rejection. Further studies are needed to clarify risks associated with pre-TXP BS, as this procedure is becoming more common in the pre-TXP population.

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