BK Virus Infection in Pediatric Renal Transplantation A. Zarauza Santoveña*, C. García Meseguer, S. Martínez Mejía, Á. Alonso Melgar, C. Fernández Camblor, M. Melgosa Hijosa, A. Peña Carrión, and L. Espinosa Román Servicio de Nefrología Pediátrica, Hospital Universitario La Paz, Madrid, Spain ABSTRACT Background. Polyomavirus BK (BKV) is a common complication after renal trans- plantation and an important cause of graft loss. The purpose of this study was to determine the incidence of BKV infection (viremia) in our population and to describe clinical features, global outcomes, and potential correlations with clinical or epidemiologic factors. Methods. This retrospective single-center study included 84 pediatric recipients of kidney transplantation from January 2006 to September 2012. BKV infection screening consisted of periodic determination of decoy cells in urine samples, confirmed by means of quantitative polymerase chain reaction test in blood. Results. Twenty-two patients (26%) developed BKV viremia. BKV replication appeared early after renal transplantation (median, 2 months). One-third of patients remained asymptomatic, and 27% presented elevated serum creatinine. Immunosuppression was reduced in 90% of patients, and 83% achieved clearance of viremia within 6 months. There was only 1 case of histologically confirmed BKV nephropathy, which evolved to graft loss despite leflunomide, intravenous immunoglobulins, and mycophenolate discontinuation. Risk of BKV viremia was associated with younger age at transplantation (5.9 y vs 10.9 years; P ¼ .001) and cadaveric donor (relative risk, 3.2; P < .05). BKV infection did not affect short-term renal function and graft survival. Conclusions. BKV viremia is very common in the pediatric renal transplant population, especially in younger children and in those receiving a kidney from cadaveric donors. It develops in the 1st months after transplantation. Reduction of immunosuppression seems to be a good therapeutic option, with high rates of clearance of the infection, although the only patient with confirmed BKV nephropathy had poor outcome. I NFECTION is a major complication of pediatric renal transplantation. It is the 1st cause of death and admis- sion to the hospital, and it may affect graft survival by direct or indirect effects [1]. BK virus (BKV) is one of the most common infections after renal transplantation. Infection by this nonenveloped double-stranded DNA virus is widespread, with seropre- valence rates >90% in young adults [2,3]. Infection usually occurs in early childhood as a nonspecific viral illness, and the virus remains latent in the urothelium and renal tubular cells. Since the great development of kidney transplantation worldwide and the appearance of new powerful immunosup- pressive drugs in the 1980s and 1990s, cases of BKV-associated nephropathy have been reported with an aggressive course and high risk of graft loss [4]. The largest pediatric cohort was reported in 2007 by Smith et al from the data of the North American Pediatric Renal Trials and Collaborative Studies registry [5], with a reported prevalence of BKV nephropathy of 4.6% (24% graft loss). More recent reports show better out- comes [6], probably owing to improvement in screening and early diagnosis. Recipient seronegative status [7e9], a high degree of immunosuppression (eg, polyclonal induction therapy [5]), and urothelium injury factors (such as permanent ureteral *Address correspondence to Alejandro Zarauza Santoveña, Servicio de Nefrología Pediátrica, Hospital Infantil La Paz, Paseo de la Castellana 261, 28046, Madrid, Spain. E-mail: alexzarauzasant@ gmail.com 0041-1345/14 http://dx.doi.org/10.1016/j.transproceed.2014.11.020 ª 2015 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010-1710 62 Transplantation Proceedings, 47, 62e66 (2015)