 Influenza surveillance information " answers the questions of where , when , and what influenza viruses are circulating . It can be used to determine if influenza activity is increasing or decreasing , but cannot be used to ascertain how many people have become ill with influenza " . For example , as of late June 2009 , influenza surveillance information showed the U.S. had nearly 28 @,@ 000 laboratory @-@ confirmed cases including 3 @,@ 065 hospitalisations and 127 deaths ; but mathematical modelling showed an estimated 1 million Americans currently had the 2009 pandemic flu , according to Lyn <unk> , a flu surveillance official with the CDC . Estimating deaths from influenza is also a complicated process . In 2005 , influenza only appeared on the death certificates of 1 @,@ 812 people in the US . The average annual US death toll from flu is , however , estimated to be 36 @,@ 000 . The CDC explains : " [ I ] <unk> is infrequently listed on death certificates of people who die from flu @-@ related complications " and hence , " Only counting deaths where influenza was included on a death certificate would be a gross underestimation of influenza 's true impact " . 
