The number of adults without health insurance jumped by 2 million from 2005 to 2006, according to a new federal report.

Uninsured Americans numbered 43.6 million last year, a 6 percent increase from 2005, according to the U.S. Centers for Disease Control and Prevention.

Almost all the increase was in the non-elderly adult population — a trend attributed to diminishing employer coverage and pricier private insurance.

The change in non-elderly adults was significant, but the overall increase was not, CDC officials said. The overall count of the uninsured has been fluctuating between 41 and 44 million over the last five years and is not really trending up, they said.

"It's kind of bobbled around," said Robin Cohen, a CDC statistician who is lead author of the report released Monday.

The CDC is one of at least three federal agencies that estimate the number of Americans without health insurance. The U.S. Census Bureau puts out what is perhaps the best-known number, but that agency's 2006 estimate is not to be released until August.

Like the Census Bureau, the CDC's estimate is based on a survey. The CDC interviewed about 75,000 Americans last year, asking if they were uninsured at that point in time. About 15 percent said yes, leading to the estimate that 43.6 million Americans were uninsured.

The number was 41.2 million in 2005; the figure has fluctuated between that mark and 43.6 million for the past five years.

But there was more than a bobble in the number of adults age 18 to 64 without health insurance. That estimate rose to 36.5 million in 2006, from 34.5 million the year before.

Rising health insurance costs have caused employers to drop coverage, and stopped people from buying it privately, experts said.

"The real key issue is we've got to find means to make health care more affordable," said Ken Thorpe, an Emory University health policy professor.

Meanwhile, the number of uninsured children has dropped from about 10 million to about 7 million from 1997 to 2006. The State Children's Health Insurance Program — a federal program to expand public health insurance programs for kids that started in 1997 — seems to be the main explanation, said Sherry Glied, a Columbia University professor who studies the uninsured.

In past policy debates, some worried that the SCHIP program would merely shift children from private coverage to public insurance without actually diminishing the number of uninsured. But the new CDC report shows that wasn't the case, Glied said.

"The kids result was interesting. I haven't really seen that in other studies," Glied said.

Between 2005 and 2006, however, there was actually a slight increase in the number of uninsured kids — from 6.5 million to 6.8 million.

Glied and others said the CDC numbers are roughly comparable to the Census Bureau estimates. The Census Bureau estimated that in 2005, 44.8 million people or 15.3 percent of the population were without health insurance.