The major clinical features, reasons for hospitalization and blood diagnostic results are summarized in Table 2 . The median duration of symptoms before admission was 2 days (IQR: 1-4 d). Presentation on admission consisted mainly in febrile respiratory illness, with a high prevalence of gastrointestinal symptoms, independently of age groups (Table 3) . Moreover, 21 children (10%) presented initially with neurological manifestations. Based upon initial clinical presentation, diagnosis of influenza A/H1N1v infection was suggested by clinicians in 56% of children (Table 2) . 74/215 (34%) children had chest X-ray confirmed pneumonia, associated in 6% with pleural effusion. Three patients had confirmed bacterial superinfection with Streptococcus pneumoniae (positive blood cultures). For five patients (2%), the influenza infection was hospital acquired.