Additional file 2.
Respondents by age and sex on each survey day, April 28 - May 26 2009. Our survey collects a cross-sectional of the US population on each survey day during April 28 and May 26 2009. The distribution of the respondents by age and sex on each survey day is presented in Figure A1.
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Ibuka et al. BMC Infectious Diseases 2010 10:296 doi:10.1186/1471-2334-10-296