The number of Americans suffering from multiple chronic conditions has grown over the past decade, according to a report by the Centers for Disease Control and Prevention (CDC). The percentage of Americans ages 45-64 with two or more chronic conditions jumped from 16 percent to 21 percent between 1999-2000 and 2009-10, according to the report. For older adults, the rate jumped to 45 percent from 37 percent over the same time period.