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First reported in March 2009 in Mexico, the 2009 pandemic influenza A (H1N1) virus has spread to more than 170 countries and caused more than 3200 deaths. Recent statistics suggest a case fatality ratio of 1.2%, but, when nonpresenters and the change to no requirement for case reporting in many countries are taken into account, experts estimate that the actual fatality ratio ranges from 0.0004% to 0.06%.
Statistics for laboratory-confirmed U.S. cases of H1N1 influenza (as of August 2009) are as follows:
Median age: 12 years
Age group with the highest infection rate: 5–24 years
Age group with the highest hospitalization rate: <51 years (vs. >65 years for seasonal influenza)
Number of deaths: 477
Number of deaths in patients <18 years: 36 (7.5% of …