1146. Thrombocytosis in Infants with Congenital Cytomegalovirus Infection Being Treated with Valganciclovir

Background Congenital CMV (cCMV) is associated with sensorineural hearing loss and neurodevelopmental disabilities. Infants with symptomatic cCMV infection benefit from 6 months of oral valganciclovir (vGCV) therapy. Neutropenia, thrombocytopenia, and hepatotoxicity are adverse effects vGCV, for which we monitor. We observed a pattern that cCMV infants treated with vGCV developed an uptrend in platelets and/or thrombocytosis (platelet count >450,000/uL) while on therapy. This observation has not previously been reported. Methods Medical records and laboratory results from our multi-disciplinary cCMV clinic led by Infectious Diseases at Lurie Children’s Hospital were reviewed (2017-2020). Data included cCMV signs/symptoms, cCMV treatment prescribed, indication for ganciclovir/vGCV treatment, and complete blood count prior to, during, and post- vGCV therapy. Results Of 21 cCMV infants referred to clinic, 14 received >1 month of vGCV for symptomatic disease, 1 discontinued vGCV < 1 month due to perceived fussiness, and 1 was part of a clinical trial. Four infants were initially treated with ganciclovir for ≤1 month and transitioned to vGCV. Of the 14 patients treated with vGCV, 10 (71%) had sensorineural hearing loss (50% unilateral), 12 (86%) had central nervous system abnormalities (including cystic lesions on head ultrasound), 5 (36%) had thrombocytopenia, and 7 (50%) were intrauterine growth restricted [Table 1]. Eleven infants (79%) developed thrombocytosis. Thirteen infants (93%) had an uptrend in platelet count [not including normalization of initial thrombocytopenia (platelets < 150,000/uL)]. Figure 1 shows platelet counts by time with respect to vGCV treatment. Neutropenia (absolute neutrophil count < 500/uL) occurred in 1 patient that required temporary discontinuation of vGCV. Table 1 Figure 1 Conclusion We observed an interesting trend of rising platelet count and the development of thrombocytosis in the majority of our cCMV patients on vGCV. Platelet elevation associated with vGCV has not previously been described. This observation is limited by small number of patients and thrombocytosis is not a definitive association/adverse effect. With increasing use of vGCV and interest in its effect on bone marrow function, this observation is notable and warrants further study. Disclosures All Authors: No reported disclosures