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Surgical site infections after simultaneous pancreas kidney and pancreas transplantation in the Swiss Transplant Cohort Study

Open AccessPublished:July 12, 2022DOI:https://doi.org/10.1016/j.jhin.2022.07.009

      Summary

      Background

      Among hospital-acquired infections, surgical site infections (SSIs) are frequent. SSI in the early post-transplant course poses a relevant threat to transplant recipients.

      Aim

      To determine incidence, risk factors for SSI and its association with post-transplant outcomes and pancreas transplant (P-Tx) recipients.

      Methods

      Adult simultaneous kidney–pancreas transplantation (SPK-T) and P-Tx recipients with a follow-up of at least 90 days were identified in the Swiss Transplant Cohort Study (STCS) dataset. Except for the categorization of SSIs according to Centers for Disease Control and Prevention (CDC) criteria, all other data were prospectively collected. Risk factors for SSI were investigated with logistic regression. A Weibull accelerated failure-time model was applied to address the impact of SSI on length of stay, correcting for transplant-related complications and delayed graft function.

      Findings

      Of 130 transplant recipients, 108 SPK-Tx and 22 P-Tx, 18 (14%) individuals developed SSI within the first 90 days after transplantation. Deep incisional (seven, 38.9%) and organ/space infections (eight, 44.4%) predominated. In the majority of SSIs (11, 61.1%; two SSIs with simultaneous identification of fungal pathogens) bacteria were detected with Enterococcus spp. being most frequent. The median duration of hospitalization after transplantation was significantly longer in recipients with SSI (median: 26 days; interquartile range (IQR): 19–44) than in patients without SSI (median: 17 days; IQR: 12–25; P = 0.002). In multivariate analysis, SSI was significantly associated with increased length of stay and prolonged the duration of hospitalization by 36% (95% confidence interval: 4–79).

      Conclusion

      SSI after SPK-Tx and P-Tx occurred at a frequency of 14%. Among pathogens, Enterococcus spp. predominated. SSI was independently associated with a longer hospitalization after transplantation.

      Keywords

      Introduction

      Simultaneous kidney–pancreas (SPK-Tx) or pancreas transplantation (P-Tx) are common treatment strategies for individuals suffering from diabetes mellitus type 1. In 2019, the Organ Procurement and Transplantation Network registered 875 SPK-Tx and 125 P-Tx transplantations in the USA, whereas in Switzerland, a total of 340 kidney transplantations and a total of 25 pancreas or islet cell transplantations were performed [
      US Department of Health & Human ServicesOrgan Procurement and Transplantation Network
      OPTN/SRTR 2019 annual data report: pancreas.
      ,].
      Among healthcare-associated infections (HAIs), surgical site infections (SSIs) are highly prevalent. Swiss data gathered in a recent point-prevalence study reported SSI as the most frequently occurring HAI [
      • Zingg W.
      • Metsini A.
      • Balmelli C.
      • Neofytos D.
      • Behnke M.
      • Gardiol C.
      • et al.
      National point prevalence survey on healthcare-associated infections in acute care hospitals, Switzerland, 2017.
      ]. Similarly, in a US point-prevalence study from 2014, SSI and pneumonia, each detected at a frequency of 20.8%, were the most frequent HAIs [
      • Magill S.S.
      • Edwards J.R.
      • Bamberg W.
      • Beldavs Z.G.
      • Dumyati G.
      • Kainer M.A.
      • et al.
      Multistate point-prevalence survey of health care-associated infections.
      ]. SSI after SPK-Tx or P-Tx was associated with poorer graft survival and prolonged duration of hospital stay [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ,
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ,
      • Perdiz L.B.
      • Furtado G.H.
      • Linhares M.M.
      • Gonzalez A.M.
      • Pestana J.O.
      • Medeiros E.A.
      Incidence and risk factors for surgical site infection after simultaneous pancreas–kidney transplantation.
      ]. In addition, SSI often requires reoperation, contributing to transplant-related morbidity [
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ]. Data on SSI after SPK-Tx and P-Tx derived from multi-centre studies remain scarce. We sought to address this important infectious complication in the early post-transplant course within the Swiss Transplant Cohort Study (STCS).

      Patients and methods

      Study design, population, and patient-related data

      This study was a nested project within the Swiss Transplant Cohort Study (STCS, www.stcs.ch, ClinicalTrials.gov Identifier: NCT01204944). All Swiss transplant centres (Basel, Bern, Geneva, St Gallen, Lausanne, and Zurich) contribute to the prospective data collection of the STCS. The STCS contains data on all solid-organ transplants performed after May 1st, 2008. Each transplant recipient is requested to grant informed consent, prompting enrolment in the STCS and inclusion into research projects. More than 93% of all transplant recipients are enrolled in the STCS, allowing comprehensive prospective data collection [
      • Koller M.T.
      • van Delden C.
      • Muller N.J.
      • Baumann P.
      • Lovis C.
      • Marti H.P.
      • et al.
      Design and methodology of the Swiss Transplant Cohort Study (STCS): a comprehensive prospective nationwide long-term follow-up cohort.
      ]. The STCS was approved by the Ethics Committees of all participating institutions. A separate approval was obtained for this nested study by the responsible Ethics Committee (Kantonale Ethikkommission Zürich, Req. 2016-01532). Among all individuals enrolled in the STCS between January 2008 and September 2021, adult patients with SPK-Tx or P-Tx and a follow-up of at least 90 days were selected (Figure 1). Individuals who received serial transplants (three SPK-Tx followed by a P-Tx, one P-Tx followed by another P-Tx) that were at least one year apart were treated as separate individuals in the analyses. In predefined time intervals, ranging from twice a week to every three months, transplant recipients are followed-up for occurrence of infections by dedicated research assistants. The research assistants are supervised by transplant infectious diseases physicians and predefined criteria for the diagnosis of infections are applied [
      • van Delden C.
      • Stampf S.
      • Hirsch H.H.
      • Manuel O.
      • Meylan P.
      • Cusini A.
      • et al.
      Burden and timeline of infectious diseases in the first year after solid organ transplantation in the Swiss Transplant Cohort Study.
      ]. SSIs were defined according to Centers for Disease Control and Prevention (CDC) criteria [
      Centers for Disease Control and Prevention
      Surgical site infection (SSI) event.
      ]. The categorization of the extent of the SSI at diagnosis was retrospectively added by patient chart review, whereas all other data derived from the prospective data collection of the STCS. Chart review was limited to individuals with a documented SSI within 90 days after transplantation in the STCS database. SSIs were categorized into superficial incisional, deep incisional, and organ/space infections accor-ding to CDC criteria [
      Centers for Disease Control and Prevention
      Surgical site infection (SSI) event.
      ]. The collection of these additional data included verification of SSIs reported in the STCS dataset by transplant infectious diseases physicians.
      Figure 1
      Figure 1Flow chart of the study population selection. SSI, surgical site infection.

      Statistical analyses

      Baseline recipient and donor characteristics were presented for SKP-Tx and P-Tx. Incidence rates were calculated for transplant-related SSIs occurring within 90 days after SKP-Tx or P-Tx. Risk factors for SSI were assessed with univariable and multivariable logistic regression. Based on findings from a previous study, cold ischaemia time and the transplant procedure (SPK-Tx vs P-Tx) were included in the multivariable model [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ]. The duration of hospitalization in patients with and without SSI was compared using the Wilcoxon rank test. In order to adjust for other factors that might alter the length of stay, a Weibull accelerated failure-time model was fitted, including the variables SSI, delayed graft function, transplant-related compli-cations, and age. The model enabled estimation of the event time ratio (ETR) for each of the covariates. Transplant-related complications that were considered likely to prolong hospitalization encompassed vascular complications affecting the graft and revision surgery or interventional drainage. Transplant outcomes, encompassing death, graft loss, need for insulin therapy, and a worsening of renal function to an estimated glomerular filtration rate <15 mL/min/1.73 m2 after SKP-Tx and death, graft loss, and need for insulin therapy after P-Tx were extracted from the STCS dataset and presented for the entire follow-up. R version 3.6.2 was used for statistical analysis and visualization [
      R Core Team
      R: a language and environment for statistical computing.
      ].

      Results

      Study population

      Overall, 108 SPK-Tx and 22 P-Tx recipients of median age 45 years (interquartile range (IQR): 37–51) and 43 years (IQR: 35–48), respectively, were included (Table I). Males contributed to 56% of SPK-Tx and to 59% of P-Tx recipients. All SPK-Tx and P-Tx were performed due to diabetes mellitus type 1. Among SPK-Tx recipients, five (5%) and among P-Tx recipients 15 (68%) individuals had had a previous transplantation. Among P-Tx recipients, 13 (59%) received the pancreas graft after previous kidney transplant. Among both SPK-Tx and P-Tx, Caucasian ethnicity was most frequent (SPK-Tx: 94, 88%; P-Tx: 21, 96%). Induction immunosuppression was administered in the vast majority of SPK-Tx and P-Tx recipients with thymoglobulin being most frequent (SPK-Tx: 85, 79%; P-Tx: 22, 100.0%). In the first week after transplantation, most SPK-Tx recipients (91, 84.3%) were started on a tacrolimus-based maintenance immunosuppressive regimen, whereas more than half of P-Tx recipients (12, 54.5%) received neither tacrolimus, cyclosporine A nor a mammalian target of rapa-mycin inhibitor. Routine perioperative antibiotic prophylaxis for SSI prevention consisted of either amoxicillin/clavulanate or piperacillin/tazobactam.
      Table IBaseline characteristics of 108 simultaneous kidney–pancreas recipients and 22 pancreas recipients
      Baseline characteristicKidney–pancreas (N = 108)Pancreas (N = 22)Total (N = 130)
      Recipient sex
       Male61 (56.0%)13 (59.1%)74 (56.5%)
       Female47 (43.5%)9 (40.9%)56 (43.5%)
      Recipient age at transplantation, median (IQR)44.7 (37.0–51.0)42.6 (34.9–48.4)44.4 (36.6–50.1)
      Recipient ethnicity
       African6 (5.6%)1 (4.5%)7 (5.4%)
       Asian1 (0.9%)01 (0.8%)
       Caucasian94 (87.9%)21 (95.5%)115 (89.1%)
       Other6 (5.6%)06 (4.7%)
      Recipient BMI, median (IQR)23.1 (21.1–25.3)22.8 (20.5–25.0)23.1 (21.1–25.3)
      Tx history5 (4.6%)15 (68.2%)20 (15.4%)
      Induction immunosuppression
       None3 (2.8%)03 (2.3%)
       Basiliximab20 (18.5%)020 (15.3%)
       Thymoglobulin83 (76.9%)19 (86.4%)102 (78.5%)
       Basiliximab and thymoglobulin2 (1.9%)1 (4.5%)3 (2.3%)
       Rituximab and thymoglobulin02 (9.1%)2 (1.5%)
      Maintenance immunosuppression
      Maintenance immunosuppressive regimen that was administered within the first week after transplantation. Other maintenance immunosuppression referred to a maintenance regimen that did not include cyclosporin A, tacrolimus, or a mammalian target of rapamycin inhibitor (mTOR inhibitor).
       Tacrolimus-based regimen91 (84.3%)10 (45.5%)101 (77.7%)
       mTOR inhibitor-based regimen1 (0.9%)01 (0.8%)
       Other16 (14.8%)12 (54.5%)28 (21.5%)
      CIT (h), median (IQR)
       Kidney10.38 (8.92–11.66)10.38 (8.92–11.66)
       Pancreas8.49 (7.18–9.57)7.95 (6.77–9.43)8.33 (7.08–9.55)
      Donor sex
       Male70 (64.8%)15 (68.2%)85 (65.4%)
       Female38 (35.2%)7 (31.8%)45 (34.6%)
      Donor age, median (IQR)33.0 (22.8–44.0)30.5 (24.0–36.8)33.0 (23.3–41.0)
      Donor type
       DBD108 (100.0%)22 (100.0%)130 (100.0%)
      IQR, interquartile range; BMI, body mass index; mTOR inhibitor, mammalian target of rapamycin inhibitor; CIT, cold ischaemia time; Tx history, prior solid organ transplant; DBD, donation after brain death.
      a Maintenance immunosuppressive regimen that was administered within the first week after transplantation. Other maintenance immunosuppression referred to a maintenance regimen that did not include cyclosporin A, tacrolimus, or a mammalian target of rapamycin inhibitor (mTOR inhibitor).

      Incidence, categorization, and aetiology of surgical site infections

      Among all 130 transplant recipients, 18 (13.8%) individuals (15 (13.9%) SPK-Tx recipients and three (13.6%) P-Tx recipients) developed SSI within the first 90 days after transplantation. Three (16.7%) SSIs were categorized as superficial incisional, seven (38.9%) as deep incisional SSIs, and eight (44.4%) as organ/space infections. There were nine (50%) bacterial SSIs (one with detection of multiple bacteria), five (27.8%) fungal SSIs (one with detection of multiple fungi), and two (11.1%) SSIs caused by fungi and bacteria. Two (11.1%) SSIs were diagnosed based on clinical findings. In the majority of SSIs after SPK-Tx, bacteria (9/15, 60%) were detected, most frequently enterococci (6/15, 40%) and coagulase-negative staphylococci (CoNS) (3/15, 20%) (Figure 2). In six SSIs at least one fungus was detected, including the species Candida albicans (4/15, 27%), Candida non-albicans (2/15, 13%), and Aspergillus fumigatus (1/15, 7%).
      Figure 2
      Figure 2Frequency of detected pathogens in surgical site infections after simultaneous pancreas–kidney and pancreas transplantation (A) and time to occurrence of surgical site infection by pathogen (B). Multiple pathogens were detected in two surgical site infections after simultaneous pancreas–kidney transplantation and in one surgical site infection after pancreas transplantation.
      After P-Tx, in two SSIs bacteria were detected, the species being Enterococcus spp., Streptococcus spp., and other anaerobic bacteria. In one SSI, a fungus was identified (Candida non-albicans).

      Risk factor analysis for surgical site infections

      Using logistic regression to identify possible risk factors for SSI, no significant association was detected with type of transplant procedure, recipient age, sex or body mass index, donor sex or age, cold ischaemia time, different induction therapies, routine perioperative antibiotic prophylaxis and the variable, if the current transplant was performed after a previous transplant (Table II). Similarly, no significant association was detected in a multivariable analysis with adjustment for type of transplant procedure and cold ischaemia time.
      Table IIUnivariate and multivariate logistic regression for identification of risk factors for surgical site infections 90 days post transplant
      Risk factorUnivariateMultivariate
      OR (95% CI)P-valueOR (95% CI)P-value
      Transplant procedure
       Kidney–pancreasReferenceReference
       Pancreas0.98 (0.21, 3.34)0.980.99 (0.26, 3.8)0.99
      Recipient sex
       FemaleReference
       Male0.72 (0.26, 1.99)0.52
      Recipient age (years)0.96 (0.91, 1.02)0.19
      Recipient BMI (kg/m2)1.03 (0.89, 1.19)0.68
      Tx history1.12 (0.24, 3.86)0.87
      CIT pancreas (min)1.00 (0.99, 1.00)0.701.00 (0.99, 1.00)0.70
      Induction immunosuppression with thymoglobulin1.09 (0.32, 5.00)0.90
      Routine perioperative antibiotic prophylaxis
       Piperacillin/tazobactamReference
       Amoxicillin/clavulanate1.50 (0.52, 4.95)0.47
      Donor sex
       FemaleReference
       Male0.62 (0.22, 1.74)0.35
      Donor age (years)1.02 (0.97, 1.06)0.51
      OR, odds ratio; CI, confidence interval; BMI, body mass index; Tx history, prior solid organ transplant; CIT, cold ischaemia time.

      Association of surgical site infections with post-transplant outcomes

      Post-transplant outcomes regarding death, graft loss, and need for insulin therapy (as well as a worsening of renal function to an estimated glomerular filtration rate <15 mL/min/1.73 m2 after SKP-Tx) were similar among transplant recipients with SSI and without SSI (Supplementary Table S1). Overall, the median length of hospital stay after transplantation was longer in patients with SSI (median: 26 days; IQR: 19–44) than in patients without SSI (17; 12–25; P = 0.002). This observation was consistent, if we focused exclusively on SPK-Tx (SSI: 23; 18–49; no SSI: 17; 12–25; P = 0.009) or P-Tx (SSI: 28; 26–31; no SSI: 15; 13–19; P = 0.055) recipients. When correcting for other possible reasons for prolonged length of hospital stay, such as delayed graft function, age- or transplant-related complications, it was found that SSIs, delayed graft function, and transplant-related complications were significantly associated with an increase in the length of stay (Table III). After adjustment for the covariates age, transplant-related complications, and occurrence of delayed graft function, patients with SSI were found to stay 36% (95% CI: 4–79) longer in the hospital than patients without SSI.
      Table IIIMultivariate accelerated failure-time model predicting time to discharge
      VariableETR (95% CI)P-value
      Surgical site infection1.36 (1.04–1.79)0.025
      Transplant-related complication1.68 (1.37–2.07)<0.001
      Delayed graft function1.40 (1.04–1.97)0.029
      Age (years)1.00 (0.9–1.01)0.767
      ETR, event time ratio.

      Discussion

      In the present cohort study on SSI after SPK-Tx or P-Tx, there was an incidence of 14% with a predominance of organ/space infections. The majority of SSIs were caused by bacteria, with Enterococcus spp. being most frequently identified. Individuals with SSI were significantly longer hospitalized after transplant compared to recipients without SSI.
      The incidence of SSI was often higher in previous studies, ranging between 20% and 50% [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ,
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ,
      • Perdiz L.B.
      • Furtado G.H.
      • Linhares M.M.
      • Gonzalez A.M.
      • Pestana J.O.
      • Medeiros E.A.
      Incidence and risk factors for surgical site infection after simultaneous pancreas–kidney transplantation.
      ,
      • Michalak G.
      • Kwiatkowski A.
      • Bieniasz M.
      • Meszaros J.
      • Czerwinski J.
      • Wszola M.
      • et al.
      Infectious complications after simultaneous pancreas–kidney transplantation.
      ]. One study reported SSI at a lower frequency with 14% for SPK-Tx and 9% for pancreas after kidney transplantation [
      • Bassetti M.
      • Salvalaggio P.R.
      • Topal J.
      • Lorber M.I.
      • Friedman A.L.
      • Andriole V.T.
      • et al.
      Incidence, timing and site of infections among pancreas transplant recipients.
      ]. One explanation for these differences could be that most studies used older data compared to the present study. It may be speculated that, due to improved practices in infection prevention, a longitudinal decrease in SSI might be observed. Furthermore, the country in which the study was performed might be relevant for the incidence of SSI. The World Health Organization reported an increased burden of HAIs in low- and middle-income countries with SSIs being the most frequent HAI [
      World Health Organization
      Report on the burden of endemic health care-associated infection worldwide. Clean care is safer care. Patient Safety.
      ].
      Among all SSIs, deep incisional and organ/space infections are the most relevant SSIs in terms of morbidity and mortality. Besides our study, few studies have addressed this categorization [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ,
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ]. Resembling the findings of Smets et al. and Natori et al., organ/space infections predominated in the present study [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ,
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ]. In contrast to Natori et al., deep incisional SSIs were found more frequent than superficial incisional SSIs [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ].
      In line with previous studies, the vast majority of SSIs was caused by bacteria, with frequent detection of Enterococcus spp. and CoNS [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ,
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ,
      • Michalak G.
      • Kwiatkowski A.
      • Bieniasz M.
      • Meszaros J.
      • Czerwinski J.
      • Wszola M.
      • et al.
      Infectious complications after simultaneous pancreas–kidney transplantation.
      ,
      • Kawecki D.
      • Kwiatkowski A.
      • Michalak G.
      • Sawicka-Grzelak A.
      • Mlynarczyk A.
      • Sokol-Leszczynska B.
      • et al.
      Surgical site infections in the early posttransplant period after simultaneous pancreas-kidney transplantation.
      ]. By contrast, Perdiz et al. reported a high proportion of Gram-negative pathogens causing SSIs [
      • Perdiz L.B.
      • Furtado G.H.
      • Linhares M.M.
      • Gonzalez A.M.
      • Pestana J.O.
      • Medeiros E.A.
      Incidence and risk factors for surgical site infection after simultaneous pancreas–kidney transplantation.
      ]. Fungal SSIs were predominantly due to Candida spp., resembling the findings from Natori et al. and Kawecki et al. [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ,
      • Kawecki D.
      • Kwiatkowski A.
      • Michalak G.
      • Sawicka-Grzelak A.
      • Mlynarczyk A.
      • Sokol-Leszczynska B.
      • et al.
      Surgical site infections in the early posttransplant period after simultaneous pancreas-kidney transplantation.
      ].
      A recent mono-centric study from Canada with inclusion of 445 patients aimed at identification of risk factors for SSI after SPK-Tx and pancreas after kidney transplantation [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ]. The authors found an increased SSI risk for SPK-Tx recipients and longer cold ischaemia time. Perdiz et al. identified acute tubular necrosis, post-transplant fistulas, and an episode of rejection as independent risk factors, whereas Smets et al. identified cefamandole prophylaxis as independent risk factor [
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ,
      • Perdiz L.B.
      • Furtado G.H.
      • Linhares M.M.
      • Gonzalez A.M.
      • Pestana J.O.
      • Medeiros E.A.
      Incidence and risk factors for surgical site infection after simultaneous pancreas–kidney transplantation.
      ]. Among the variables addressed, we identified no significant risk factor for SSI. However, our analysis might be hampered by the low frequency of SSI in our cohort and the overall limited number of SPK-Tx and P-Tx recipients. Our cohort did not include data on the individually administered perioperative antibiotic prophylaxis, but if we considered the different routinely administered perioperative prophylaxis, no significant association with SSI was found.
      Data on transplant outcomes due to SSI among SPK-Tx and P-Tx patients are still scarce. In a Canadian cohort of SPK and pancreas after kidney recipients, a longer hospital stay and 16-fold odds for graft loss within three months post transplant was reported [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ]. Smets et al. observed two graft losses in direct relation to SSI among 20 patients with SSI and a significant longer hospital stay in recipients with SSI [
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ]. In line with prior studies, we confirmed a prolonged duration of hospitalization for transplant recipients with SSIs [
      • Natori Y.
      • Albahrani S.
      • Alabdulla M.
      • Vu J.
      • Chow E.
      • Husain S.
      • et al.
      Risk factors for surgical site infection after kidney and pancreas transplantation.
      ,
      • Smets Y.F.
      • van der Pijl J.W.
      • van Dissel J.T.
      • Ringers J.
      • de Fijter J.W.
      • Lemkes H.H.
      Infectious disease complications of simultaneous pancreas kidney transplantation.
      ,
      • Perdiz L.B.
      • Furtado G.H.
      • Linhares M.M.
      • Gonzalez A.M.
      • Pestana J.O.
      • Medeiros E.A.
      Incidence and risk factors for surgical site infection after simultaneous pancreas–kidney transplantation.
      ]. The application of a Weibull accelerated failure-time model enabled a more accurate estimate of the association between the investigated variables and prolongation of hospital stay. These findings might be helpful for identification of individuals with likely prolonged hospital stay and the expected extent of prolongation by the occurrence of associated variables. A better understanding of these associations could be crucial for optimized allocation of resources in healthcare. The current study identified no significant differences among the further assessed outcome variables.
      Strengths of this study include the multi-centric design with almost exclusive use of prospectively collected data. The STCS dataset is highly representative for transplantations performed in Switzerland given an enrolment of more than 90% of all solid organ transplantations performed in Switzerland [
      • Koller M.T.
      • van Delden C.
      • Muller N.J.
      • Baumann P.
      • Lovis C.
      • Marti H.P.
      • et al.
      Design and methodology of the Swiss Transplant Cohort Study (STCS): a comprehensive prospective nationwide long-term follow-up cohort.
      ]. The use of widely established CDC definitions for SSIs enables insights into severity of SSIs and will allow comparisons with future studies.
      The present study also has some limitations. The categorization of SSIs was assessed retrospectively. The overall low number of SSIs limited statistical power and thus hindered more detailed statistical analyses. No information was collected on the administration of perioperative prophylaxis per individual patient. Data on routinely used perioperative antibiotic prophylaxis were gathered, but there might have been adaptations due to pre-transplant colonization of transplant recipients.
      To conclude, SSIs were detected at a similar frequency after SPK-Tx and P-Tx. SSI was associated with significantly longer hospitalization after transplant procedure.

      Conflict of interest statement

      P.W.S. received travel grants from Pfizer and Gilead, speaker's honorary from Pfizer, and fees for advisory board activity from Pfizer and Gilead outside of the submitted work. All other authors declared no conflicts of interest.

      Funding sources

      P.W.S. is supported by the academic career programme ‘Filling the Gap’ of the Medical Faculty of the University of Zurich. This study was performed in the framework of the Swiss Transplant Cohort Study, supported by the Swiss National Science Foundation , the Swiss University Hospitals(G15) and transplant centres.

      Appendix A. Supplementary data

      The following is the Supplementary data to this article:

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