A study of poverty in America shows the number of people living in extreme poverty has grown sharply during the past decade, erasing gains the U.S. made in reducing poverty during the 1990s.

The Brookings Institution, a research group based in Washington, says the number of people living in extreme-poverty areas – in communities where at least 40 percent of all residents have incomes so low they are known as “below the poverty line” – increased by more than one-third.

The survey compares the number of Americans living in poverty in 2000 to poverty estimates for the period 2005-2009. The United States defines poverty as an annual income of $22,300 or less for a family of four people.

The nation's worst economic downturn in 70 years left millions of people out of work, and many others still working were forced out of their homes when they could no longer pay mortgages.

Brookings' report, titled “The Re-Emergency of Concentrated Poverty” (http://goo.gl/ftPLA), says the number of Americans living in poverty has risen to an historic high since 2000: 46.2 million people. Midwestern and southern portions of the U.S. have been hardest hit, with manufacturing jobs lost and a large number of houses taken over by banks in loan foreclosures.