OBJECTIVE To monitor group/area/time epidemic features of influenza cases in Jiangsu province annually, to analyze variation and epidemical features of advantage seasonal influenza strains in 2009-2011 to provide basis for its control and prevention. METHODS All Influenza-like illnesses between Jane/2009 and Dec/2011 were surveyed through 14 influenza network laboratories, case samples were collected, viruses were isolated and RNA was extracted and detected, the relative data were sorted and analyzed. RESUL...