By Susan Morse

An estimated 3.2 million more Americans became uninsured in 2017, according to a new Gallup and Sharecare poll.

The percentage of adults without health insurance was 12.2 percent at the end of 2017, up 1.3 percent from a record low of 10.9 percent in the fourth quarter of 2016.

The 1.3-point increase is the largest single-year increase Gallup and Sharecare have measured since beginning to track the rate in 2008, before the Affordable Care Act went into effect.

It represents an estimated 3.2 million Americans who entered the ranks of the uninsured in 2017.

The Gallup-Sharecare Well-Being Index is based on more than 25,000 interviews with adults aged 18 and older from October 1 to December 31.

The number of uninsured is expected to climb, as the Congressional Budget Office has projected that 4 million more people will be without health insurance in 2019 due to the Republican tax bill that ended the individual mandate to get insurance. By 2027, that number is expected to climb to 13 million, the CBO said.

The repeal of the individual insurance mandate would increase the uninsured population and raise uncompensated care costs, hurting operating margins and cash flow, Moody's Investors Service said in December. The tax reform law would have negative credit implications for non-profit hospitals and healthcare systems, the report said.

Beyond a negative credit rating and additional uncompensated care, hospitals face an uninsured population that will likely forego wellness and preventative care, leading to more ER visits for more serious health conditions.