About 25 million Americans are expected to gain coverage under the health law, commonly known as Obamacare. Starting Oct. 1, as many as 7 million uninsured Americans will begin shopping for private plans through government-run exchanges, with many people eligible to have their premiums subsidized by taxpayers. On Jan. 1, Medicaid programs for low-income people will be expanded in about half the U.S. states.

The increase in newly insured patients arrives at a time when the nation has 15,230 fewer primary-care doctors than it needs, according to an Aug. 28 assessment by the U.S. Department of Health and Human Services. And emergency rooms report being strained with visits that have risen at twice the rate of population growth.

“It’s like we’re handing out bus tickets and the bus is already full,” said Perry Pugno, vice president for medical education at the American Academy of Family Physicians, by telephone. “The shortfall of primary-care access is not an insignificant problem, and it’s going to get worse.”

Almost half of all uninsured, non-elderly adults had a chronic condition, based on a 2005 report by the Urban Institute and the University of Maryland. One in six with hypertension reported no visits to health professionals in a year.