(CNN) - The coverage gains achieved by the Affordable Care Act are starting to erode.
The uninsured rate for those ages 45 to 64 jumped to 10.3% in 2018, up from 9.3% a year earlier, according to a report from the Centers for Disease Control and Prevention published Thursday.
It's the first time a government study has shown an increase in the rate, though polling and research groups had previously found that people had been losing their health insurance since President Donald Trump took office.
The increase comes two years into Trump's administration, which has sought to undermine and dismantle the Affordable Care Act as well as add restrictions to Medicaid. Enrollment in both programs has been slipping.
The landmark health care law is credited with extending coverage to millions of Americans, prompting the uninsured rate for non-elderly adults to plummet from 22.3% in 2010, the year Obamacare passed, to a low of 12.4% in 2016. Last year, it stood at 13.3%, though the agency noted the difference was not statistically significant.
The CDC report does not explain why the rate for those ages 45 to 64 has climbed while remaining stable for younger adults. These middle-age Americans have the lowest uninsured rate among non-elderly adults. The share of this cohort without insurance began creeping up in 2015, but the changes were not statistically significant until now.
The uninsured rate serves as a gauge for Trump's impact on coverage. Other nongovernmental research groups have previously reported evidence that it has been on the rise.
The Kaiser Family Foundation reported in December that the number of uninsured non-elderly Americans rose by nearly 700,000 in 2017 and the rate inched up to 10.2%, from 10%. It used federal American Community Survey data, which draws on a larger sample size than the survey the Census Bureau uses to determine the official uninsured rate, which showed no significant change between 2016 and 2017.
Driving the increase was an upswing in the uninsured rate in states that did not expand Medicaid, particularly among non-Hispanic blacks and those living above the poverty line within those states, Kaiser found.
While coverage rates rose and then stabilized in the first few years after the Affordable Care Act's implementation, "now we are starting to see signs that things are going in a different direction," said Rachel Garfield, associate director in Kaiser's Program on Medicaid and the Uninsured.
The most common reason why people remained uninsured is because the cost of coverage is too high, according to Kaiser. Some may not be aware that they are entitled to federal assistance.
Meanwhile, Gallup found that the uninsured rate for adults was 13.7% in the fourth quarter of 2018, the highest in more than four years and well above the low point of 10.9% in 2016. That represents an increase of about 7 million uninsured people, according to Gallup, which polls Americans on their health coverage status.
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