CDC Estimates of 2009 H1N1 Influenza Cases, Hospitalizations and
Deaths in the United States, April – November 14, 2009 This
website is archived for historical purposes and is no longer
being maintained or updated. For updated information on the
current flu season, see the CDC Seasonal Flu website. December
10, 2009, 1:00 PM ETApril – October 17 Estimates Estimating the
number of individual flu cases in the United States is very
challenging because many people with flu don’t seek medical care
and only a small number of those that do seek care are tested.
More people who are hospitalized or die of flu-related causes
are tested and reported, but under-reporting of hospitalizations
and deaths occurs as well. For this reason CDC monitors
influenza activity levels and trends and virus characteristics
through a nationwide surveillance system and uses statistical
modeling to estimate the burden of flu illness (including
hospitalizations and deaths) in the United States. When the 2009
H1N1 flu outbreak began in April