It has been documented that the adverse outcome, particularly a severe form (i.e. entering ICU or death), after influenza infection is associated with numerous risk factors, including age and underlying medical conditions of the patients. Nolan et al. in a recent study on pandemic or seasonal influenza have observed that infants, the elderly and people suffering from chronic diseases are of high risks for adverse outcome [11] ; some other authors have demonstrated significant adverse clinical outcome in patients aged $20 years and patients delayed in hospital admission [12, 13] . Nevertheless, only adult hospitalized cases were included in the present study.