Brief Communication. Introduction

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1 American Journal of Transplantation 2015; 15: Wiley Periodicals Inc. Brief Communication C Copyright 2015 The American Society of Transplantation and the American Society of Transplant Surgeons doi: /ajt Risk Factors for Infection With Carbapenem-Resistant Klebsiella pneumoniae After Liver Transplantation: The Importance of Pre- and Posttransplant Colonization M. Giannella 1, *, M. Bartoletti 1, M. C. Morelli 2, S. Tedeschi 1, F. Cristini 1, F. Tumietto 1, E. Pasqualini 3, I. Danese 1, C. Campoli 1, N. Di Lauria 1, S. Faenza 4, G. Ercolani 3, R. Lewis 1, A. D. Pinna 3 and P. Viale 1 1 Infectious Diseases Unit, Department of Medical and Surgical Sciences, Sant Orsola Hospital, Alma Mater University of Bologna, Bologna, Italy 2 Internal Medicine Unit for the Treatment of Severe Organ Failure, Department of Medical and Surgical Sciences, Sant Orsola Hospital, Alma Mater Studiorum University of Bologna, Bologna, Italy 3 Liver and Multiorgan Transplant Unit, Department of Medical and Surgical Sciences, Sant Orsola Hospital, Alma Mater Studiorum University of Bologna, Bologna, Italy 4 Anesthesia Unit, Department of Medical and Surgical Sciences, Sant Orsola Hospital, Alma Mater Studiorum University of Bologna, Bologna, Italy Corresponding author: Maddalena Giannella, maddalena.giannella@libero.it Improved understanding of risk factors associated with carbapenem-resistant-klebsiella pneumoniae (CR-KP) infection after liver transplantation (LT) can aid development of effective preventive strategies. We performed a prospective cohort study of all adult patients undergoing LT at our hospital during 30- month period to define risk factors associated with CR- KP infection. All patients were screened for CR-KP carriage by rectal swabs before and after LT. No therapy was administered to decolonize or treat asymptomatic CR-KP carriers. All patients were monitored up to 180 days after LT. Of 237 transplant patients screened, 41 were identified as CR-KP carriers (11 at LT, 30 after LT), and 20 developed CR-KP infection (18 bloodstream-infection, 2 pneumonia) a median of 41.5 days after LT. CR-KP infection rates among patients non-colonized, colonized at LT, and colonized after LT were 2%, 18.2% and 46.7% (p < 0.001). Independent risk factors for CR-KP infection identified by multivariate analysis, included: renal-replacement-therapy; mechanical ventilation > 48 h; HCV recurrence, and colonization at any time with CR-KP. Based on these four variables, we developed a risk score that effectively discriminated patients at low versus higher risk for CR- KP infection (AUC 0.93, 95% CI , p < 0.001). Our results may help to design preventive strategies for LT recipients in CR-KP endemic areas. Abbreviations: AKI, acute kidney injury; BSI, bloodstream infection; CR-KP, carbapenem-resistant Klebsiella pneumoniae; CVC, central venous catheter; HCV, hepatitis C virus; IQR, interquartile range; LT, liver transplant; MELD, model for end-stage liver disease; MV, mechanical ventilation; RIFLE, risk, injury, failure, loss and end-stage kidney disease; ROC, receiver operating curve; RRT, renal replacement therapy; SD, standard deviation; SOT, solid organ transplantation Received 22 August 2014, revised 23 November 2014 and accepted for publication 25 November 2014 Introduction Over the last decade, carbapenem resistant-klebsiella pneumoniae (CR-KP) have spread worldwide becoming a serious healthcare problem in a number of countries, including Italy (1). Infections with CR-KP are associated with high morbidity and mortality, particularly among vulnerable patient populations such as those undergoing solid organ transplantation (SOT) (2). Liver transplant (LT) recipients are reported to be at uniquely high risk for acquiring and dying from CR-KP infection (3,4). In endemic areas, the incidence of CR-KP infection following LT is approximately 5%, with crude mortality rates reported between 25 and 71% (3 7). Given the poor prognosis and the limited therapeutic options, prevention of CR-KP infection in the LT setting is of paramount importance. Recommendations for the prevention of CR-KP transmission in healthcare facilities include: optimizing compliance with hand hygiene and contact precautions, minimizing the use of indwelling devices, implementing antimicrobial stewardship programs, and active screening for CR-KP colonization (8). However, universal screening of asymptomatic LT candidates and/or recipients is not a standard of 1708

2 CR-KP Infection in Liver Transplantation care, and there are limited data suggesting this approach is beneficial (9). Furthermore, strategies for managing CR-KP colonized patients undergoing transplantation have not been systematically evaluated (e.g. deferring LT, selective intestinal decontamination, peri-operative prophylaxis with antibiotics active against CR-KP). On the other hand, empiric use of antibiotic regimens active against CR-KP places a patient at increased risk for toxicity and the emergence of pan-resistant isolates (10). Previous studies performed in non-transplant populations have reported that source control of the infection and prompt initiation of an adequate antibiotic therapy are associated with improved survival from CR-KP infection (2,11,12). However, relying on culture-based techniques to identify CR- KP leads to a h delay from sample collection to initiation of appropriate therapy (7). Thus, strategies to administer appropriate therapy in a more timely manner are needed. In CR-KP endemic areas, a possible strategy may be to use colonization status in conjunction with epidemiologic risk factors to identify colonized patients at highest risk for infection who could benefit from empirical therapy active against CR-KP. However, few studies have examined the impact of CR-KP colonization and unique risk factors for CR- KP infection after LT. With this aim, we performed a prospective observational study of all patients undergoing LT at our hospital during a 30-month period to ascertain the incidence and risk factors for CR-KP infection. Our goal was to establish an institutional clinical risk prediction model (score) that could facilitate decisions regarding empiric treatment of CR-KP in colonized LT recipients. Materials and Methods Study design and patients We performed a prospective observational cohort study of all adult ( 18 years) patients undergoing LT at our hospital, from June 2010 to December We examined possible risk factors for CR-KP infection within 6 months after LT to develop a clinical risk score for CR-KP infection. The study was approved by our Institutional Review Board and due to its noninterventional observational design, patient informed consent was waived. Setting S. Orsola-Malpighi Hospital is a 1450-bed tertiary care University Hospital in Bologna (Northern Italy) with an average of admissions per year. The hospital hasan activelt program, performing an average of 90 procedures per year. The first case of CR-KP invasive infection (bacteremia) in our institution was detected in April 2010 and increased steadily after September 2010 up to two cases per patient days in June After August 2011, we implemented a multifaceted infection control program directed to reduce CR- KP transmission, which resulted in a progressive reduction of CR-KP BSI to 0.96 cases per patient days (13). Transplant management During the study period, all LT candidates were screened monthly by rectal swab (RS) for CR-KP carriage starting at the time of inclusion in the waiting list until the time of transplant. RS were then repeated once weekly after LT until hospital discharge. Isolation and contact precautions were activated for CR-KP carriers, but no pharmacological interventions were used, including selective intestinal decontamination, specific surgical prophylaxis, or targeted antimicrobial treatment, in asymptomatic patients. Patients who developed a CR-KP infection were treated with a combination regimen including high-dose carbapenem administered by extended infusion and at least one drug with in vitro activity (colistin, tigecycline, and gentamycin) depending on the infection site, as previously reported (14,15). For the purpose of this study, only the first CR-KP infection episode was considered for the analysis. All the patients received 48 h peri-operative prophylaxis with ampicillinsulbactam. After induction with high-dose prednisone, the standard immunosuppression protocol consisted of tacrolimus and low-dose prednisone. Biopsy-proven rejection episodes were treated with 1 g methylprednisolone. Antithymocyte globulin (ATG) was administered in cases of steroid-refractory rejection. Liver biopsies were performed only in patients with unexplained cholestasis or marked elevation in serum transaminases. HCV antiviral treatment was started in presence of histological features of HCV recurrence with fibrosis >F1 according to Metavir score (16). CMV seronegative patients, who received an organ from a CMV positive donor, received oral valganciclovir 900 mg/daily as prophylaxis until 90 days after transplant. All CMV seropositive patients were screened weekly for CMV DNAemia by whole-blood quantitative polymerase chain reaction until 90 days after LT. If CMV DNAemia exceeded copies/ml, patients were started on induction treatment with ganciclovir 5 mg/kg/bid or oral valgancyclovir 900 mg/bid (17). All patients were administered 160/800 mg trimethoprim/sulfamethoxazole three times weekly for 12 months posttransplant as prophylaxis for Pneumocystis jirovecii. Tailored antifungal prophylaxis was administered to patients with risk factors for invasive aspergillosis or candidiasis as described elsewhere (18). All suspected infection episodes were evaluated and managed in collaboration with a dedicated team of infectious disease specialists. Data Potential risk factors for CR-KP infection were collected 30-days prior to transplantation or the onset of infection, and up to 180 days after transplant or CR-KP isolation, whichever occurred last. Variables were collected in a standardized case form included: demographic data (sex, age); date of hospitalization before LT; prior hospital or ICU admission in the previous 90 days; prior antibiotic exposure in the last month, and the cause and severity of liver disease according to the Model for End-stage Liver Disease (MELD) score calculated at LT. Other underlying diseases were analyzed according to the Charlson s comorbidity index. We documented donor and recipient CMV serostatus; peri-operative complications (vascular, biliary, bleeding, and need of re-intervention); and acute kidney injury (AKI) according to RIFLE criteria (19), with or without need of renal replacement therapy (RRT). The number of patient days of mechanical ventilation (MV) were recorded as well as graft dysfunction (primary or secondary), biopsy-proven rejection, re-transplantation, histological recurrence of hepatitis C virus (HCV) infection; colonization with CR-KP before or after LT; infection with CR-KP after LT with infection site and sepsis severity according to international guidelines (20). Additionally, we collected data on the dates of ICU and hospital discharge and 30-day all-cause mortality. Definitions CR-KP carriage was defined as the isolation of CR-KP from a rectal swab in absence of symptoms and signs of invasive infection. Every sample positive for CR-KP other than blood cultures, including urine, respiratory samples, surgical site and other skin cultures in asymptomatic patients were considered as colonization besides stool. However, because other body American Journal of Transplantation 2015; 15:

3 Giannella et al sites were not routinely cultured to screen for CR-KP carriage, only rectal cultures were used to CR-KP colonization as a risk factor for infection. CR-KP infection was defined according to CDC criteria (21). Microbiology Rectal swabs were inoculated on a chromogenic agar plate (Oxoid Brilliance CRE, Thermo Fisher Scientific, United Kingdom) containing a carbapenem antibiotic as selective agent. Clinical specimens were processed in accordance with the CLSI guidelines and isolates were identified using the Vitek 2 semi-automated system (Biomerieux, Marcy l Etoile, France) (22). Carbapenem MICs for K. pneumoniae were confirmed by E-test (Biomerieux). Carbapenemase production was confirmed by disc-diffusion synergy test (Rosco Diagnostica, Taastrup, Denmark). All the strains resistant to > 1 carbapenem were defined as CR-KP. All MICs were interpreted according to EUCAST guidelines. Statistical analysis Categorical variables were expressed as absolute numbers and their relative frequencies. Continuous variables were expressed as mean standard deviation (SD) if normally distributed, or as median and interquartile range (IQR) if non-normally distributed. Patients who developed a CR-KP infection within 180 days after LT were compared with those who did not develop a CR- KP infection during that period. Categorical variables were compared using Pearson chi-square or Fisher s exact test when appropriate. Continuous variables were compared using Student s t or Mann Whitney U test according to their distribution. We calculated the incidence of CR-KP infection after LT by dividing the number of new episodes observed during the study period by the overall number of patient days in the study cohort computed from the day of transplantation until day 180 or patient death. All the variables with a p-value 0.1 at the univariate analysis were entered into a Cox regression model after verifying proportional hazards. CR-KP rectal carriage acquired at any time was included into the model, instead of colonization after LT, to improve model sensitivity. Patients were considered from the day of LT up to 180 days or before in case of CR-KP infection or death. To develop a risk score for CR-KP infection, a point value according to the b-coefficient was assigned to all the variables that maintained statistical significance (p < 0.05) in the final multivariate regression model. Summation of these points resulted in a quantitative score assigned to each patient in the database. The sensitivity, specificity and positive and negative predictive value of the score was analyzed at different score thresholds using area under the receiver operating characteristics (ROC) curve. The optimal risk score breakpoint was established using the Youden s J statistic. Calibration of the risk model was assessed by comparing Cox-model predicted probabilities at various risk score thresholds versus observed event rates estimated by the Kaplan Meier method. Results Overall, 237 patients underwent LT during the study period. CR-KP infection developed in 20 (8.4%) within a median of 41.5 days (IQR ) after LT. Thus, the incidence rate of CR-KP infection was 5.07 cases per LT recipient days. Bloodstream infection (BSI) was diagnosed in 18/20 patients, which was classified as a primary infection in 8 patients, catheter-related infection in 2 patients, and infection secondary to pneumonia, deep surgical site infection, and cholangitis in 4, 3, and 1 patients, respectively. The remaining two patients had pneumonia diagnosed with isolation of 10 5 cfu/ml CR-KP from the bronchoalveolar lavage. Criteria of sepsis, severe sepsis and septic shock were presented at the infection onset in 4 (20%), 6 (30%) and 10 (50%) patients, respectively. CR-KP rectal carriage was detected in 41 patients. Of these, 11 were colonized at LT while 30 acquired colonization within a median of 14 (IQR 7 29) days after LT. Of the 11 patients colonized at the time of LT, 7 had a negative rectal swab within a median of 30 days before transplantation, and 4 had a positive rectal swab collected at 40, 30 and 13 days before transplantation in 1, 2, and 1 patient, respectively. The rates of CR-KP infection among non-colonized patients, those colonized at LT, and patients who acquired colonization after LT were 2%, 18.2%, and 46.7% (p < 0.001), respectively. Of the 11 patients colonized at LT, 2 (18.2%) developed infection at 10 and 131 days after LT, respectively. Of the 30 patients who acquired CR-KP colonization after LT, 14 (46.7%) developed infection within a median of 19 days (IQR ) after colonization was detected and a median of 40 days (IQR ) after LT. Overall, four patients with negative surveillance cultures for CR-KP developed a CR-KP BSI within 41.5 (IQR ) days after LT. These episodes consisted of two secondary BSIs (each from biliary and lower respiratory tract), one primary BSI and one catheter-related BSI (thus an exogenous source). Risk factors for CR-KP infection and predictive model Comparison of patients with and without CR-KP infection are shown in Table 1. Significant differences were found for prior exposure to any antibiotic, higher median MELD at LT, AKI and need of RRT after LT, re-intervention, biliary stenosis, need of MV for > 48 h, CMV infection (DNAemia copies per ml), graft dysfunction, and retransplantation. Among antibiotic classes, previous treatment with meropenem or fluoroquinolone antibiotics was associated with significantly higher risk of CR-KP infection. CR-KP rectal carriage was a significant risk factor for CR-KP infection, specifically if patients were colonized after LT. Multivariate analysis revealed the need of RRT after LT (HR 4.75, 95%CI , p ¼ 0.004), MV > 48 h (HR 6.81, 95% CI , p ¼ 0.001), HCV recurrence (HR 9.71, 95% CI , p ¼ 0.001) and CR-KP rectal carriage at any time (HR 13.86, 95% CI , p < 0.001) as independent risk factors for CR-KP infection (data shown in Table 2). Assignment of points based on the beta coefficients for these four independent variables generated an individual risk score for each patient ranging from 0 to 9 (mean 1.4, 95% CI ). Risk scores were significantly higher among patients who developed CR-KP infection within 180 days after LT versus patients who did not develop infection (mean 5.3 vs. 1.04, p < 0.001). ROC curve analysis suggested that the risk score could acceptably discriminate low versus higher-risk patients, with an area under the curve of 0.93 (95% CI , 1710 American Journal of Transplantation 2015; 15:

4 Table 1: Comparison of patients with and without CR-KP infection within 180 days after liver transplantation CR-KP Infection in Liver Transplantation Total, n ¼ 237 (100%) Patients without CR-KP infection, n ¼ 217 (91.5%) Patients with CR-KP infection, n ¼ 20 (8.5%) p Demographic data Age (years) [media ( SD)] 57 ( 12) 55 ( 14) 63 ( 2.8) 0.87 Sex, male 158 (66.7) 143 (65.9) 15 (75) 0.46 Comorbidities Charlson index [media ( SD)] 6.34 ( 2.2) 6.6 ( 2.6) 6 ( 1.4) 0.15 Prior hospital admission 112 (47.3) 98 (45.2) 14 (70) 0.02 Prior ICU admission 15 (6.3) 15 (6.9) 3 (6) 0.69 Underlying liver disease 1 HCV 84 (51) 58 (50) 26 (55) 0.57 Alcohol 53 (32) 36 (31) 17 (37) 0.39 Hepatocellular carcinoma 57 (35) 40 (36) 17 (36) 0.45 Fulminant liver failure 12 (5.1) 12 (5.5) 0 (0) 0.33 MELD at LT (median, IQR) 21, , , Prior antibiotic exposure 160 (67.5) 142 (65.4) 18 (90) 0.01 Meropenem 23 (6.3) 17 (7.8) 6 (30) Fluoroquinolones 37 (15.6) 19 (13.4) 8 (40) Rectal swab positive for CR-KP 41 (17.3) 25 (11.5) 16 (80) <0.001 Carriage at LT 11 (4.6) 9 (4.1) 2 (10) 0.23 Carriage acquired after LT 30 (12.7) 16 (7.4) 14 (70) <0.001 Intraoperative complication Hypotension 8 (3.4) 8 (3.7) 0 (0) 0.48 Bleeding 22 (9.3) 18 (8.3) 4 (20) 0.09 Anastomotic leakage 8 (3.4) 8 (3.7) 0 (0) 0.48 Postoperative complication Acute kidney injury 56 (23.6) 43 (19.8) 13 (65) <0.001 Renal replacement therapy 28 (11.8) 17 (7.8) 11 (55) <0.001 Re-intervention 27 (11.4) 19 (8.8) 8 (40) Biliary stenosis 19 (9) 12 (5.5) 7 (33) <0.001 Mechanical ventilation > 48 h 56 (23.6) 42 (19.4) 14 (70) <0.001 CMV DNAemia copies/ml 33 (13.9) 25 (11.5) 8 (40) Graft complication PGNF 11 (4.6) 7 (3.2) 4 (20) <0.001 Any rejection episode 17 (4.2) 14 (6.5) 3 (15) 0.16 Retransplantation 14 (4.1) 8 (4.1) 5 (25) HCV recurrence 21 (8.8) 17 (7.8) 4 (20) 0.08 Outcome Days of ICU stay (median, IQR) 2 6, , , <0.001 Days of hospital stay (median, IQR) 2 18, , , < day post-lt mortality 26 (11) 17 (7.3) 9 (45) <0.001 CR-KP, carbapenem resistant Klebsiella pneumoniae; DGF, delayed graft function; ICU intensive care unit; IQR, interquartile range; LT, liver transplantation; PGNF, primary graft non-function; SD, standard deviation. 1 Some patient presented more than one cause of liver disease. 2 These variables where calculated from the day of transplantation. Table 2: Multivariate analysis of risk factors for CR-KP infection after liver transplantation Variable Hazard ratio 95% CI p Risk score points Renal replacement therapy Mechanical ventilation > 48 h Histological recurrence of HCV CR-KP rectal carriage at any time < CI, confidence interval; CR-KP, carbapenem resistant K. pneumoniae; LT, liver transplantation. American Journal of Transplantation 2015; 15:

5 Giannella et al Cut-off Sens Spec PPV NPV 0 100% 0 8.4% - >0 95% 63.1% 19.2% 99.3% >2 90% 82.9% 32.7% 98.9% >3 85% 90.8% 45.9% 98.5% >4 75% 96.3% 65.2% 97.7% >5 45% 99.5% 90% 95.2% > % % AUC=0.93, 95%CI , p<0.001 Figure 1: Discrimination of the risk model by the area-under receiver-operative-characteristic curve analysis. p < 0.001) (Figure 1). At a cut-off > 3, sensitivity, specificity, positive and negative predictive values of the model were 85%, 91%, 46% and 98.5%, respectively. Calibration of the model is shown in Figure 2. Frequencies of the risk factors and of the CR-KP infection for each risk stratification threshold are shown in Table 3. Discussion We found that the incidence of CR-KP infection is higher in LT recipients than in the general hospital population in our center. CR-KP infection occurs primarily after the first month of transplantation, and is more likely to occur in Score Predicted vs. Observed BSI (Gray=Cox Model Predicted; Black KM Observed) Cumulative probability of CR-KP infection Score 7 (n=10) Score 5 (n=13) Score 4 (n=14) Score 3 (n=200) Days after transplant Figure 2: Calibration of the risk model by comparing Cox-model predicted probabilities at risk score thresholds 3, 4, 5 and 7 versus observed event rates estimated by Kaplan Meier analysis American Journal of Transplantation 2015; 15:

6 Table 3: Frequencies of the model risk factors and of CR-KP infection for different stratification thresholds CR-KP Infection in Liver Transplantation Risk factor Score 3 n ¼ 200 (%) Score 4 n ¼ 14 (%) Score 5 n ¼ 13 (%) Score 7 n ¼ 10 (%) CR-KP rectal carriage At LT After LT 18 (9) 9 (4.5) 9 (4.5) 0 (0) 0 (0) 0 (0) 13 (100) 2 (15.4) 11 (84.6) 10 (100) 0 (0) 10 (100) MV > 48 h 26 (13) 13 (92.9) 7 (53.8) 10 (100) Need of RRT 3 (1.5) 13 (92.9) 3 (23.1) 9 (90) HCV recurrence 15 (7.5) 2 (14.3) 3 (23.1) 1 (10) CR-KP infection 3 (1.5) 2 (14.3) 6 (46.2) 9 (90) CR-KP, carbapenem-resistant K. pneumoniae; LT, liver transplantation; MV, mechanical ventilation; RRT, renal replacement therapy. patients with medical or surgical complications after transplant. Although colonization was the most important risk factor for CR-KP infection after LT, patients colonized prior to LT had a lower risk of infection compared with those who acquired colonization after LT. Additionally, colonization alone was not predictive of infection. Our rate of CR-KP infection in colonized patients after LT is similar to that reported in the literature (7). In previous studies, CR-KP infection occurred earlier after LT, within the first 4 weeks. However, Clancy et al. described 17 transplant recipients (8 liver, 6 intestinal, 2 lung and 1 liver kidney) who developed CR-KP bacteremia within a median of 163 days after transplant, with 47% of episodes observed after >180 days of transplant (6). Our study suggests that the higher CR-KP infection risk in transplant patients is not specific to surgical complications associated with LT. Furthermore, our percentage of patients with a bloodstream involvement (90%) is in agreement with previous reports of CR-KP infection in the LT population (7). Nearly half of the patients (44.4%) had a primary BSI without an identifiable source. For secondary BSIs, 50% of the infections originated from the lung and 50% from the abdomen (3 deep surgical site infections and 1 cholangitis). The lack of urinary infections in our study cohort reflects stricter diagnostic criteria applied in our cohort compared to previous studies. The relatively high percentage of patients with pulmonary infection confirms recent observations of an increasing prevalence of pneumonia caused by multidrug resistant Gram negative bacteria early after LT (23,24). American Journal of Transplantation 2015; 15: We believe this is one of the first studies to specifically focus on the identification of risk factors for CR-KP infection after LT. Previous studies included mixed patient populations consisting of critically ill patients, SOT recipients, patients with hematological diseases and those admitted to medical and surgical wards (25,26). Several risk factors for CR-KP infection may be unique to LT recipients, and may not emerge during multivariate analysis of more heterogeneous population. Such variables include: the severity of underlying liver disease, particularly the MELD at LT; perioperative complications (i.e. biliary stenosis, anastomosis leakage, bleeding) that often require re-intervention; acute renal failure with potential need of RRT; graft dysfunction including rejection and in extreme cases the need of re-transplantation; and finally infection with immunomodulatory viruses such as CMV and HCV. In our analysis of these variables, we found that RRT, MV>48 h and histological evidence of HCV recurrence were independent risk factors for CR-KP infection in CR-KP colonized patients. This is the first study evaluating the active screening for CR- KP rectal carriage in LT candidates and recipients. Although there is consensus regarding the need for screening all LT candidates and potential donors in hospitals during a CR-KP outbreak (7,9,27), opinions are divided concerning the need for universal screening in hospitals where CR-KP is endemic. There are also limited published data addressing the question of continued screening for CR-KP rectal carriage after LT. In a previous case-control study, we found that patients colonized before LT did not have a higher incidence of CR-KP infection after LT versus non-colonized patients. However, 6/20 patients of the control group acquired CR-KP colonization after LT (28). Here, we confirmed these data and show that acquisition of CR-KP colonization after LT was strongly associated with developing an infection. Therefore, we believe that universal screening for CR-KP carriage is necessary not only during outbreaks, but also in hospitals where the CR-KP is endemic, and that it should be performed both before and after transplantation. Our risk score has a high negative predictive value, suggesting that it can help clinicians identify the majority of colonized patients after LT with a low probability for developing CR-KP infection. Risk stratification may help limit empiric overuse of antibiotics such as high-dose carbapenems, colistin, aminoglycosides, and tigecycline, which contribute to further emergence of MDR infections and/or adverse effects in patients. Our study has some limitations. It is a monocentric study, therefore our data may be different from that found in other centers, with different screening modalities and surgeon-id consultant interaction. Nevertheless, the incidence, source, and crude mortality of CR-KP infection observed in our cohort are similar to that described by other centers. Another limitation of our study may be the use of the culture technique for CR-KP screening instead of the molecular methods, which are more sensitive in the detection of CR-KP colonization (29). 1713

7 Giannella et al However, to minimize this potential bias, cultures were swabbed in parallel to nonselective media for detection of enterobacterial microbiota as a quality control procedure for submitted swabs. In patients suspected of having low-level colonization (e.g. patients treated for any reason with antibiotics potentially active against CR-KP), we also performed a preliminary broth enrichment step aimed at increasing the sensitivity of the test. We did not routinely culture non-rectal sites to assess CR-KP colonization status. In a recent study of risk factors for CR-KP BSI among a large cohort of rectal carriers, colonization at other sites beyond stool was the main predictor of BSI (25). Hence, the impact of colonization at other sites may have been underestimated in our study. Finally, we only confirmed carbapenem resistance phenotypically and did not perform genetic confirmation of resistance mechanisms. Recent studies suggest heterogeneity in biofilm formation, macrophage-mediated killing and level of drug resistance according to the molecular differences among CR-KP strains (even when clonally related, e.g. ST258) (30). Indeed, some authors have proposed therapeutic algorithms according to genotype characteristics of the strains (31). This information combined with a validated clinical risk score may improve the management of LT recipients suspected as having a CR-KP infection in the future. Finally, our proposed risk score requires prospective validation before use in clinical practice; a need that we plan to address with a prospective multicenter study. To conclude, medical and surgical complications associated with LT may increase the risk of CR-KP infection among colonized patients. These data provide the background needed to design preventive strategies currently advocated for all transplant centers in regions with endemic CR-KP resistance. Disclosure The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation. References 1. Munoz-Price LS,Poirel L, Bonomo RA, et al. Clinical epidemiology of the global expansion of Klebsiella pneumoniae carbapenemases. Lancet Infect Dis 2013; 13: Patel G, Huprikar S, Factor SH, Jenkins SG, Calfee DP. Outcomes of carbapenem-resistant Klebsiella pneumoniae infection and the impact of antimicrobial and adjunctive therapies. Infect Control Hosp Epidemiol 2008; 29: Kalpoe JS, Sonnenberg E, Factor SH, et al. Mortality associated with carbapenem-resistant Klebsiella pneumoniae infections in liver transplant recipients. Liver Transpl 2012; 18: Lubbert C, Becker-Rux D, Rodloff AC, et al. Colonization of liver transplant recipients with KPC-producing Klebsiella pneumoniae is associated with high infection rates and excess mortality: a casecontrol analysis. Infection 2014; 42: Bergamasco MD, Barroso Barbosa, de Oliveira M, et al. 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