Basic characteristics/denigraphics of the patients Given the unique nature of 2009 pandemic H1N1, both suspected and laboratory confirmed cases had to be reported to the Chinese Centre for Disease Control and Prevention (CCDC). During May 7 th and August 12 th , 2009, the number of reported laboratory-confirmed H1N1 cases was 2668. In this study, we analyzed the data of 885 adult hospitalized patients, accounting for 68.6% of the total confirmed cases. The major demographic and clinical characteristics of these patients are summarized in Table 1 .