The percentage of cases which required hospitalisation during the two outbreaks in Lazio was high (57%). This can be partly explained by the well known underreporting of cases by general practitioners and paediatricians, as compared to hospital physicians. The number of cases requiring hospitalisation, especially during July-September 2006, was sufficiently high to create problems to the hospital system. The inadequate number of isolation beds in hospitals may represent a serious problem in case of occurrence of an epidemic due to a more aggressive infective agent, such as SARS or pandemic flu.