Respiratory syncytial virus-positive bronchiolitis in hospitalized infants is associated with thrombocytosis.

BACKGROUND Secondary thrombocytosis is associated with a variety of clinical conditions, one of which is lower respiratory tract infection. However, reports on thrombocytosis induced by viral infections are scarce. OBJECTIVES To assess the rate of thrombocytosis (platelet count > 500 x 10(9)/L) in hospitalized infants with bronchiolitis and to investigate its potential role as an early marker of respiratory syncytial virus infection. METHODS Clinical data on 469 infants aged < or = 4 months who were hospitalized for bronchiolitis were collected prospectively and compared between RSV-positive and RSV-negative infants. RESULTS The rate of thrombocytosis was significantly higher in RSV-positive than RSV-negative infants (41.3% vs. 29.2%, P=0.031). The odds ratio of an infant with bronchiolitis and thrombocytosis to have a positive RSV infection compared to an infant with bronchiolitis and a normal platelet count was 1.7 (P= 0.023, 95% confidence interval 1.07-2.72). There was no significant difference in mean platelet count between the two groups. CONCLUSIONS RSV-positive bronchiolitis in hospitalized young infants is associated with thrombocytosis.