ATLANTA (AP) — A survey shows one in five Americans say their families are having trouble paying their medical bills. Worse, half of those who are struggling say they are unable to pay anything toward those debts.

The survey of 52,000 people was conducted by the Centers for Disease Control and Prevention from January through June last year. It's the first time the government agency has looked at the issue in such a comprehensive way.

Peter Cunningham, who studies the issue for an independent health policy research group, says it may be the largest such study ever done on the matter.

Lower-income people struggled the most. They were three times more likely to have difficulty paying their medical bills over the past year.

It's the first time the CDC has asked the medical debt question in its long-standing, in-person health survey, so there is no previous data to compare it with.

But another organization, the nonpartisan Center for Studying Health System Change, where Cunningham works, believes the number of people struggling with medical debt actually has been stable in the last five years.

The statistic of one in five who struggle with medical bills was reported by Cunningham and his colleagues in a smaller study in 2007 at the start of the recession. That figure remained the same in their 2010 survey and that's surprising, since the ranks of the unemployed and uninsured grew by millions.

“As the number of uninsured increased, and there was higher unemployment, you'd expect that more people would report having problems paying medical bills,” Cunningham said.

However, he and other experts believe there's something else at play here: Many Americans are just cutting back on doctor visits, prescription purchases and other health care spending.

CDC report: http://www.cdc.gov/nchs