Elevated tacrolimus levels among COVID-19 kidney transplant recipients are associated with worse disease severity and clinical outcomes.

BACKGROUND: The therapeutic effects of immunosuppressive drugs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections causing coronavirus disease 2019 (COVID-19) are being actively investigated. However, COVID-19's potential effects on serum calcineurin inhibitor levels have only been described recently. This study aimed to evaluate COVID-19's effect on tacrolimus levels in renal transplant recipients with moderate to severe symptoms and to assess their potential correlation with disease severity. MATERIALS AND METHODS: We retrospectively investigated 50 kidney transplant recipients with moderate to severe COVID-19. Their tacrolimus trough level on admission was compared to baseline levels, and their laboratory measurements and clinical course were reviewed on days 1 (admission), 7, 14, and 28. RESULTS: We found that 90% of patients had admission tacrolimus trough levels above baseline, with a mean increase of 176%. In addition, 71% had tacrolimus trough levels ≥ 50% above baseline, and 40% had supra-therapeutic trough levels of > 15 ng/mL. Supra-therapeutic trough levels were associated with greater hypoxemic respiratory failure, acute kidney injury, and increased 30-day mortality. CONCLUSION: Elevated tacrolimus levels occur in many renal transplant recipients with moderate to severe COVID-19 and are associated with worse clinical outcomes. Close drug monitoring is crucial to avoid toxicities and minimize over-immunosuppression complications.

Weight-based vs fixed dosing of darbepoetin alfa for anemia following kidney transplantation.

PURPOSE: Post-transplantation anemia (PTA) is common in kidney transplant recipients, with patients frequently treated with erythropoietin-stimulating agents such as darbepoetin alfa. The optimal dosing for darbepoetin alfa remains controversial. METHODS: This retrospective cohort study involved kidney transplant recipients who received darbepoetin alfa at 2 clinics. Patients were stratified into 2 groups: those who received a fixed dose of 200 µg and those who received a weight-based dose of 0.45 µg/kg. The dosing interval varied depending on clinical response, clinic visit timing, and frequency allowed by insurance. The primary outcome was achieving a hemoglobin concentration of at least 10 g/dL without blood transfusion by 12 weeks after darbepoetin alfa initiation. RESULTS: Of the 110 patients in the study, 45% received weight-based dosing and 55% received fixed dosing. Darbepoetin alfa was initiated significantly earlier after transplantation in the fixed-dose group (median of 14 vs 20 days; P = 0.003). The weight-based group received more doses of darbepoetin alfa (median of 4 vs 2 doses; P = 0.002) and had a significantly lower cumulative exposure to darbepoetin alfa (125 vs 590 µg; P < 0.001). The median time between doses was 9 days (interquartile range, 7-14 days) in the weight-based group and 12 days (7-32 days) in the fixed-dose group (P = 0.04). Patients in the weight-based group more frequently achieved the primary outcome (67.3% vs 47.5%; P = 0.059). There was no significant difference in secondary or safety outcomes between the groups. CONCLUSION: Weight-based and fixed dosing approaches for darbepoetin alfa were not different in the achievement of a hemoglobin concentration of at least 10 g/dL without blood transfusion at 12 weeks after darbepoetin alfa initiation, with significantly lower cumulative darbepoetin alfa utilization in the weight-based group. Weight-based dosing of darbepoetin alfa in PTA appears to be safe and effective, with the potential for significant patient and health-system cost savings.

Early outcomes of kidney transplant recipients from donors with severe SARS-CoV-2 pneumonia: A report of 5 cases.

BACKGROUND: Transplanting kidneys from donors with a recent history of severe SARS-CoV-2 pneumonia is uncommon due to concerns about the risk of viral transmission and the quality of kidneys from these donors. To date, there are no conclusive data on viral transmission from extrapulmonary solid organ transplants. Given the prevalence of SARS-CoV-2 infections in potential donors, shortage of kidneys available for transplantation, and low risk of viral transmission, we developed a clinical protocol for accepting kidneys from donors with recent severe SARS-CoV-2 pneumonia who demonstrate preserved kidney function. MATERIALS AND METHODS: We collected data on early outcomes of 5 kidney transplant recipients from 4 deceased donors hospitalized for severe SARS-CoV-2 infection. RESULTS: Donor creatinine ranged from 0.51 to 0.60 mg/dL and kidney donor profile index (KDPI) from 14 to 52%. Three of the five kidneys were from donation after circulatory death. All recipients were fully vaccinated, and 4/5 received post-exposure prophylactic monoclonal antibody treatment. While 3 recipients had delayed graft function, all had excellent graft function at 3 or 4 weeks post-operatively. None of the recipients displayed signs or symptoms of SARS-CoV-2 infection post-transplant. CONCLUSION: Our findings suggest that kidney grafts from donors with a recent history of severe SARS-CoV-2 infection but with preserved kidney function can be safely used and have good early outcomes.

Association of the COVID-19 pandemic with increased adherence among prevalent hemodialysis patients.

BACKGROUND: During the COVID-19 pandemic, there has been a reduction in emergency department visits and hospital admissions. We hypothesized that hemodialysis patients were decreasing their hospital visits and increasing their dialysis adherence during the COVID-19 pandemic. MATERIAL AND METHODS: This is a retrospective analysis of hemodialysis patients treated in the seven American Renal Associates (ARA) dialysis centers in the Dallas-Fort Worth metropolitan area. We conducted a "before-and-after" study using existing clinical data to examine patient adherence with hemodialysis between January 1 and March 14, 2020 (pre-COVID) and March 15 to May 18, 2020 (COVID) time periods. Data points included missed treatments, shortened treatments, post-dialysis weight, and hospital visits. Finally, we conducted an anonymous survey in which patients reported their hemodialysis adherence. RESULTS: Data analysis was performed on 556 patients. Significantly fewer patients missed a single treatment in the COVID vs. pre-COVID time periods (44.1 vs. 58.6%; p < 0.001). Significantly fewer patients finished their treatment with a post-dialysis weight more than 1 kg above their estimated dry weight in the COVID vs. pre-COVID time periods (31.7 vs. 38.9%, p = 0.01). Finally, there was a reduction in total hospital visits during the COVID vs. pre-COVID periods (12.6 vs. 19.4%; p = 0.002). The anonymous survey showed patients reporting increased adherence with hemodialysis and restriction of salt and water intake. CONCLUSION: The COVID time period was associated with increased adherence with hemodialysis and decreased hospital visits, and patients were conscious of these changes.

Association between dd-cfDNA levels, de novo donor specific antibodies, and eGFR decline: An analysis of the DART cohort.

BACKGROUND: Donor-derived cell-free DNA (dd-cfDNA) is a marker of allograft injury in transplant recipients; however, the relationship between dd-cfDNA and other clinical parameters associated with adverse allograft outcomes is not well-characterized. METHODS: We performed a retrospective analysis of kidney transplant recipients from the DART cohort (ClinicalTrials.gov Identifier: NCT02424227) to evaluate the associations between eGFR decline, de novo donor-specific antibodies (dnDSA), and dd-cfDNA. RESULTS: Both elevated dd-cfDNA (≥1%) and dd-cfDNA variability (≥.34%) in the first post-transplant year were associated with decline in eGFR ≥25% in the second year (21.4% vs. 4.1%, P = .005; 25% vs. 3.6%, P = .002, respectively). Compared to samples from DSA negative patients, samples from patients with concurrent de novo HLA DSAs had higher dd-cfDNA levels (P < .0001). DISCUSSION: Abnormalities in dd-cfDNA levels are associated with clinical parameters commonly used as surrogate endpoints for adverse allograft outcomes, raising the possibility that molecular injury as characterized by dd-cfDNA could help identify patients at risk of these outcomes.

Serum sickness induced by alemtuzumab in a kidney-pancreas transplant recipient.

Serum sickness is an immune-complex-mediated hypersensitivity reaction that was first noted in the early 1900s in patients receiving heterologous antisera, such as horse antitetanus or antidiphtheria serum. This condition is primarily self-limited; however, in its acute state, it can cause severe symptoms of fever, rash, polyarthritis, or polyarthralgias. In solid organ transplantation, this condition is frequently reported in association with the use of rabbit anti-thymocyte globulin and chimeric murine monoclonal antibodies such as rituximab. Alemtuzumab, designed as a humanized monoclonal antibody against CD52, is expected to be less immunogenic. Here, we report a case of serum sickness associated with alemtuzumab induction therapy in a kidney-pancreas dual-organ recipient.

A Model for Glomerular Filtration Rate Assessment in Liver Disease (GRAIL) in the Presence of Renal Dysfunction.

Estimation of glomerular filtration rate (eGFR) in patients with liver disease is suboptimal in the presence of renal dysfunction. We developed a model for GFR assessment in liver disease (GRAIL) before and after liver transplantation (LT). GRAIL was derived using objective variables (creatinine, blood urea nitrogen, age, gender, race, and albumin) to estimate GFR based on timing of measurement relative to LT and degree of renal dysfunction (www.bswh.md/grail). The measured GFR (mGFR) by iothalamate clearance (n = 12,122, 1985-2015) at protocol time points before/after LT was used as reference. GRAIL was compared with the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Modification of Diet in Renal Disease (MDRD-4, MDRD-6) equations for mGFR < 30 mL/min/1.73 m2 . Prediction of development of chronic kidney disease (mGFR < 20 mL/min/1.73 m2 , initiation of chronic dialysis) and listing or receipt of kidney transplantation within 5 years was examined in internal cohort (n = 785) and external validation (n = 68,217, 2001-2015). GRAIL had less bias and was more accurate and precise as compared with CKD-EPI, MDRD-4, and MDRD-6 at time points before/after LT for low GFR. For mGFR < 30 mL/min/1.73 m2 , the median difference (eGFR-mGFR) was GRAIL: 5.24 (9.65) mL/min/1.73 m2 as compared with CKD-EPI: 8.70 (18.24) mL/min/1.73 m2 , MDRD-4: 8.82 (17.38) mL/min/1.73 m2 , and MDRD-6: 6.53 (14.42) mL/min/1.73 m2 . Before LT, GRAIL correctly classified 75% as having mGFR < 30 mL/min/1.73 m2 versus 36.1% (CKD-EPI), 36.1% (MDRD-4), and 52.8% (MDRD-6) (P < 0.01). An eGFR < 30 mL/min/1.73 m2 by GRAIL predicted development of CKD (26.9% versus 4.6% CKD-EPI, 5.9% MDRD-4, and 10.5% MDRD-6) in center data and needing kidney after LT (48.3% versus 22.0% CKD-EPI versus 23.1% MDRD-4 versus 48.3% MDRD-6, P < 0.01) in national data within 5 years after LT. Conclusion: GRAIL may serve as an alternative model to estimate GFR among patients with liver disease before and after LT at low GFR.

Treatment of recurrent, post-kidney transplant membranoproliferative glomerulonephritis with plasmapheresis and rituximab: A case report and literature review
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Membranoproliferative glomerulonephritis is known to recur after kidney transplantation and may lead to allograft loss. Although an optimal treatment has not been determined, B-cell targeted therapies are now increasingly used as first-line agents, based on growing data showing antibodies as key players in the pathogenesis of membranoproliferative glomerulonephritis. Here, we report a case of recurrent immune complex-mediated membranoproliferative glomerulonephritis 3 years after a living-donor kidney transplant. Treatment with plasmapheresis and rituximab resulted in immediate and sustained improvement in allograft function.
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Cell-Free DNA and Active Rejection in Kidney Allografts.

Histologic analysis of the allograft biopsy specimen is the standard method used to differentiate rejection from other injury in kidney transplants. Donor-derived cell-free DNA (dd-cfDNA) is a noninvasive test of allograft injury that may enable more frequent, quantitative, and safer assessment of allograft rejection and injury status. To investigate this possibility, we prospectively collected blood specimens at scheduled intervals and at the time of clinically indicated biopsies. In 102 kidney recipients, we measured plasma levels of dd-cfDNA and correlated the levels with allograft rejection status ascertained by histology in 107 biopsy specimens. The dd-cfDNA level discriminated between biopsy specimens showing any rejection (T cell-mediated rejection or antibody-mediated rejection [ABMR]) and controls (no rejection histologically), P<0.001 (receiver operating characteristic area under the curve [AUC], 0.74; 95% confidence interval [95% CI], 0.61 to 0.86). Positive and negative predictive values for active rejection at a cutoff of 1.0% dd-cfDNA were 61% and 84%, respectively. The AUC for discriminating ABMR from samples without ABMR was 0.87 (95% CI, 0.75 to 0.97). Positive and negative predictive values for ABMR at a cutoff of 1.0% dd-cfDNA were 44% and 96%, respectively. Median dd-cfDNA was 2.9% (ABMR), 1.2% (T cell-mediated types ≥IB), 0.2% (T cell-mediated type IA), and 0.3% in controls (P=0.05 for T cell-mediated rejection types ≥IB versus controls). Thus, dd-cfDNA may be used to assess allograft rejection and injury; dd-cfDNA levels <1% reflect the absence of active rejection (T cell-mediated type ≥IB or ABMR) and levels >1% indicate a probability of active rejection.

Biological Variation of Donor-Derived Cell-Free DNA in Renal Transplant Recipients: Clinical Implications.

BACKGROUND: Previous studies have demonstrated that donor-derived cell-free DNA (dd-cfDNA) found in circulating blood of transplant recipients may serve as a noninvasive biomarker of allograft rejection. To better interpret the clinical meaning of dd-cfDNA, it is essential to understand the biological variation of this biomarker in stable healthy recipients. This report establishes the biological variation and clinical reference intervals of dd-cfDNA in renal transplant recipients by using an analytically validated assay that has a CV of 6.8%. METHODS: We sampled venous blood at patient surveillance visits (typically at posttransplant months 1-4, 6, 9, and 12) in a 14-center observational study. Patients with stable renal allograft function spanning ≥3 serial visits were selected. We used AlloSure®, a targeted next-generation sequencing-based approach, to measure dd-cfDNA in the plasma and computed the intraindividual CV (CVI) and interindividual CV (CVG), the index of individuality (II), and reference change value (RCV). RESULTS: Of 93 patients, 61% were men, 56% were Caucasian, mean age was 49 years, and 63% were deceased donor kidney recipients. Of 380 blood samples, the dd-cfDNA median value was 0.21% (interquartile range 0.12%-0.39%) and the 97.5th percentile was 1.20%. In 18 patients with an average of 4.1 tests, the CVI was 21%, CVG was 37%, II was 0.57, and RCV was 61%. CONCLUSIONS: In a renal transplant recipient, a dd-cfDNA level above 1.2% is out of range and potentially abnormal. A serial increase of up to 61% in level of dd-cfDNA in a patient may be attributable to biological variation.Clinicaltrials.gov Identifier: NCT02424227.

Routine ultrasonography surveillance of native kidneys for renal cell carcinoma in kidney transplant candidates.

Renal cell carcinoma (RCC) has a high incidence in the kidney transplant population and annual surveillance detects these tumors early in their natural history. Minimal guidelines exist regarding RCC surveillance in ESRD patients awaiting transplant. A retrospective review of our kidney transplant database examined the outcomes of annual ultrasonographic surveillance during initial kidney transplant evaluation and upon annual reassessment. Of 2642 patients listed for transplant, 145 patients were found to have masses during initial kidney transplant evaluation or annual imaging consistent with new complex cystic disease or RCC. A total of 71 patients had RCC identified, with 52 found on initial kidney transplant evaluation and 19 identified on annual surveillance. Male gender and African-American race were independently associated with RCC (P<.05). RCC was detected a median of 2.0 years after listing (two annual ultrasonography studies). Patients with complex cysts were more likely to undergo transplantation (48.7%) compared to patients with RCC (21.1%; P<.001). There was no significant difference in survival between RCC patients and those found to have complex cystic disease, suggesting incidental RCC can be diagnosed early in the natural history and at a curable stage through implementation of a biennial surveillance program.

Late presentation of adenovirus-induced hemorrhagic cystitis and ureteral obstruction in a kidney-pancreas transplant recipient.

We report a late presentation of adenovirus-induced renal allograft and bladder infection causing azotemia and hemorrhagic cystitis in a patient 5 years after simultaneous kidney-pancreas transplantation. Adenovirus has been increasingly recognized as a cause of morbidity and mortality in both solid organ and stem cell transplant recipients. We wish to emphasize the importance of early detection, as treatment options involve reduction of immunosuppression, followed by the addition of antiviral agents and supportive care.

West Nile virus infection in kidney and pancreas transplant recipients in the Dallas-Fort Worth Metroplex during the 2012 Texas epidemic.

BACKGROUND: In 2012, the United States experienced one of its worst West Nile virus (WNV) epidemics, reporting 5,387 human cases and final death toll of 243. Texas was at the epicenter of the outbreak, with 1,875 reported cases and 89 deaths that year. The Texas outbreak centered mainly in the Dallas-Fort Worth area where 30 deaths were reported. We report three cases of severe WNV infection complicated by meningoencephalitis in our organ transplant population. METHODS: Clinical data were collected from chart review. Therapy and outcomes on three identified patients were reviewed and compared with previously reported cases of WNV infection in kidney/pancreas transplant recipients and the general population. RESULTS: Two recipients of kidney and one recipient of a combined kidney and pancreas transplant were treated at our center for WNV infection. All three patients presented with a rapid decline in mental status within 24 hours of admission consistent with meningoencephalitis. Diagnosis was made based on detection of WNV IgM in the serum. All patients received intravenous immunoglobulin (IVIG) therapy at 400 mg/kg × 3 to 4 doses. As a result, two patients had a full recovery, and one patient died. CONCLUSION: Transplant recipients have a higher risk of neurologic complications from WNV infection. In areas where WNV is endemic, clinicians must have a high index of suspicion when treating patients presenting with fever, headache, and confusion. Full recovery in two of three patients suggests a potential role of IVIG therapy in controlling active WNV infection, particularly in immunosuppressed patients.

Whole-organ pancreas transplantation at Baylor Regional Transplant Institute: a chance to cure diabetes.

The success of pancreas transplantation has improved over the past several decades with advancements in surgical technique, immunosuppressive medicines, and immunologic testing. We retrospectively reviewed our experience with pancreas transplantation from 1995 to 2008. At the Baylor Regional Transplant Program, 151 pancreas transplants were performed in 147 patients: 135 were simultaneous pancreas-kidney transplants, 10 were pancreas transplants after kidney transplants, and 6 were pancreas transplants alone. Follow-up information was available for 138 patients. The 1-year acute cellular rejection rate was 31.6%; the 30-day surgical reexploration rate was 10%; and the technical failure rate was 5.3%. Five-year pancreas graft survival rates were 67% for simultaneous pancreas and kidney transplants and 50% for pancreas transplants after kidney transplants. These outcomes exceed expected results as calculated by the Scientific Registry of Transplant Recipients. In addition, the median time to transplant was 3.8 months, compared with a US median of 14.1 months. Pancreas transplantation is currently the closest thing to a cure for diabetes and should be given as an option for diabetic patients with or without end-stage renal disease.

Indications for combined liver and kidney transplantation: propositions after a 23-yr experience.

The frequency of combined liver and kidney transplants (CLKT) persists despite the pronounced scarcity of organs. In this review, we sought to ascertain any factors that would reduce the use of these limited commodities. Seventy-five adult CLKT were performed over a 23-yr period at our center, 29 (39%) of which occurred during the Model for End-stage Liver Disease (MELD) era. Overall, patient survival rates were 82%, 73%, and 62% at one, three, and five yr, respectively. There was no difference in patient survival based either on pre-transplant hemodialysis status or by glomerular filtration rate (GFR) at the time of transplant. Patients undergoing a second CLKT or a liver retransplantation at the time of CLKT had a survival rate of 30% at three months. In the MELD era, patient survival was unchanged (p = NS) despite an older recipient population (p = 0.0029) and a greater number of hepatitis C patients (p = 0.0428). In summary, patients requiring liver retransplantation with concomitant renal failure should be denied CLKT. Renal allografts may also be spared by implementing strict criteria for renal organ allocation (GFR < 30 mL/min at the time of evaluation) and considering the elimination of preemptive kidney transplantation in CLKT.

Use of two expanded-criteria-donor renal allografts in a single patient.

The disparity between the number of available renal donors and the number of patients on the transplant waiting list has prompted the use of expanded-criteria-donor (ECD) renal allografts to expand the donor pool. ECD allografts have shown good results in appropriately selected recipients, yet a number of renal allografts are still discarded. The use of dual renal transplantation may lower the discard rate. Additionally, the use of perfusion systems may improve acute tubular necrosis rates with these allografts. We report a successful case of a dual transplant with ECD allografts using a perfusion system. The biopsy appearance and the pump characteristics were suboptimal for these kidneys, making them unsuitable for single transplantation; however, the pair of transplanted kidneys provided increased nephron mass and functioned well. We recommend that ECD kidneys that are individually nontransplantable be evaluated for potential dual renal transplantation. Biopsy criteria and perfusion data guidelines must be developed to improve the success rates with ECD dual renal allografts. Finally, recipient selection is of utmost importance.

WAGR syndrome: a clinical review of 54 cases.

WAGR syndrome is a rare genetic disorder characterized by a de novo deletion of 11p13 and is clinically associated with Wilms' tumor, aniridia, genitourinary anomalies, and mental retardation (W-A-G-R). Although the genotypic defects in WAGR syndrome have been well established, the large variety of phenotypic manifestations of the syndrome has never been reported. We report on 54 cases of WAGR syndrome to demonstrate both the classical clinical signs and nonclassical manifestations found in a large population of individuals with this disorder. An understanding of WAGR syndrome and its clinical findings can provide important insight regarding the functions of the involved genetic region. Recommendations for diagnosis, evaluation, and surveillance of patients with WAGR syndrome are also presented.

Rabies encephalomyelitis: clinical, neuroradiological, and pathological findings in 4 transplant recipients.

BACKGROUND: Three patients received solid organ transplants from a common donor and were subsequently discharged from the hospital following an uneventful hospital course. Within 30 days, all 3 organ recipients returned to the hospital with varying symptoms that progressed to rapid neurological deterioration, coma, and death. OBJECTIVE: To describe the clinical, neuroradiological, and pathological findings of rabies virus infection in organ transplant recipients infected from a common donor. DESIGN: Case series involving a common donor and 3 organ recipients ascertained through review of clinical course and autopsy findings. A fourth case was determined by review of pending autopsy cases in which death occurred within the same time interval. Portions of postmortem central nervous system and organ tissues were frozen and formalin-fixed. Fluids and tissues were also collected for cultures, serology, and molecular studies. Postmortem fluids and tissues and antemortem fluids and tissues from all 4 transplant recipients and serum and banked lymphocyte or spleen cells from the donors were sent to the Centers for Disease Control and Prevention for further evaluation. SETTING: Transplant unit of an urban teaching hospital. RESULTS: Antemortem cerebrospinal fluid analysis for 3 of the 4 recipients was consistent with a viral etiology. Neuroimaging and electroencephalogram studies were suggestive of an infectious encephalitis or a toxic encephalopathy. Initial laboratory testing did not demonstrate an infectious etiology. Postmortem histologic analysis, immunohistochemistry, electron microscopy, and direct fluorescence antibody testing revealed rabies virus infection. Serological testing done postmortem confirmed rabies virus infection in the common donor. CONCLUSIONS: These cases demonstrate a risk for transmitting rabies virus infection through solid organ and tissue transplantation, and this diagnosis should be considered in any rapidly progressing neurological disease.

Transmission of rabies virus from an organ donor to four transplant recipients.

BACKGROUND: In 2004, four recipients of kidneys, a liver, and an arterial segment from a common organ donor died of encephalitis of an unknown cause. METHODS: We reviewed the medical records of the organ donor and the recipients. Blood, cerebrospinal fluid, and tissues from the recipients were tested with a variety of assays and pathological stains for numerous causes of encephalitis. Samples from the recipients were also inoculated into mice. RESULTS: The organ donor had been healthy before having a subarachnoid hemorrhage that led to his death. Encephalitis developed in all four recipients within 30 days after transplantation and was accompanied by rapid neurologic deterioration characterized by agitated delirium, seizures, respiratory failure, and coma. They died an average of 13 days after the onset of neurologic symptoms. Mice inoculated with samples from the affected patients became ill seven to eight days later, and electron microscopy of central nervous system (CNS) tissue demonstrated rhabdovirus particles. Rabies-specific immunohistochemical and direct fluorescence antibody staining demonstrated rabies virus in multiple tissues from all recipients. Cytoplasmic inclusions consistent with Negri bodies were seen in CNS tissue from all recipients. Antibodies against rabies virus were present in three of the four recipients and the donor. The donor had told others of being bitten by a bat. CONCLUSIONS: This report documenting the transmission of rabies virus from an organ donor to multiple recipients underscores the challenges of preventing and detecting transmission of unusual pathogens through transplantation.