ABSTRACT
Population aging is a major trend shaping the 21st century. Due in large part to public health effectiveness in infectious disease surveillance and control, an unparalleled increase in life expectancy ranks among the greatest achievements of the 20th century. Between 1900 and 2000 in the United States (US), life expectancy improved by almost 60%, increasing from 49 to 77 years (Arias, 2002). This extraordinary public health achievement now presents unprecedented challenges for public health policy in the 21st century.
