1. U.S. Census Bureau. 2004. U.S. interim projections by age, sex, race and Hispanic origin. Available at: http://www.census.gov/ipc/www/usinterimproj/natprojtab02a.pdf. Accessed July 1, 2006.
2. Russo CA, Elixhauser A. Hospitalizations in the elderly population, 2003. Statistical brief #6. 2006. Agency for Healthcare Research and Quality. Rockville (MD). Available at: http://www.hcup-us.ahrq.gov/reports/statbriefs/sb6.pdf. Accessed July 1, 2006.
3. Infectious disease hospitalizations among older adults in the United States from 1990 through 2002;Curns;Arch Intern Med,2005
4. The aging of the immune system;Grubeck-Loebenstein;Adv Immunol,2002
5. Human immunosenescence: the prevailing of innate immunity, the failing of clonotypic immunity, and the filling of immunological space;Franceschi;Vaccine,2000