The clinical significance of thrombocytosis in children with viral respiratory tract infections

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<b>Background:</b> Reactive thrombocytosis (PLT&gt;500) is estimated between 3-13% in hospitalized children and was previously found to be associated with RSV infections and younger age. <b>Aims:</b> We sought to examine the clinical significance of thrombocytosis in young children admitted with influenza-like illness (ILI). <b>Methods:</b> A database analysis of patients admitted to the Hadassah Medical Centers over a 7 year period who underwent a nasopharyngeal aspirate. Included were children under 3 years of age admitted for ILI. Association between platelet count, aspirate results and clinical and demographic parameters were evaluated. Multivariate linear regression models assessed the association between high platelet count and length of stay (LOS). <b>Results:</b> Of 6096 patients included in the database 4399 met inclusion criteria (median age 7.2 (2.4 – 14.4) months, 59% male, median LOS of 3 (2-5) days). Nasopharyngeal aspirate results were positive in 2351 children (58%). Median platelet count was slightly, and significantly higher with an RSV infection (median= 403 (319-507) vs. 392 (301-491), p=0.003). However, when adjusting for demographics, high platelet count was associated with younger age (difference (95%CI) = -40.0 (-47.2- -32.8), p&lt;0.001) and not with the type of infection. On multivariate linear regression analysis, high platelet count was the only independent predictor of a prolonged LOS (difference (95%CI) = 0.10 (0.03-0.20), p=0.001). <b>Conclusion:</b> In the largest cohort to date, we show that in hospitalized pediatric patients admitted with ILI, a high platelet count is associated with a younger age and is an independent predictor of hospital LOS.