Aetna Inc.'s decision to withdraw from Affordable Care Act exchanges in Pennsylvania and 10 other states means that Independence Blue Cross will be the only major firm offering individual plans for 2017 to Southeastern Pennsylvania residents.

In its announcement Monday, Aetna, of Hartford, Conn., cited a second-quarter loss of $200 million on the exchange business because a large number of newly insured people needed high-cost care.

Aetna serves about 31,000 Pennsylvanians through the marketplace, about 6 percent of the state's individual health insurance market, according to the Pennsylvania Insurance Department. Coverage for those people will not change this year.

In New Jersey, Aetna has not sold plans on the ACA exchange, where subsidies are available.

"I am disappointed Aetna is withdrawing from the federal health insurance marketplace in Pennsylvania, and many other states, due to financial losses on the state exchanges created under the Affordable Care Act," Pennsylvania Insurance Commissioner Teresa Miller said Tuesday.

Aetna, which has operations in Blue Bell, is the third major insurer to significantly cut back its participation in the public exchanges. The others were UnitedHealth Group Inc. and Humana Inc. Aetna wants to buy Humana for $29 billion, despite the U.S. Department of Justice's opposition.

"Providing affordable, high-quality health-care options to consumers is not possible without a balanced risk pool," Aetna chief executive Mark T. Bertolini said. "Fifty-five percent of our individual on-exchange membership is new in 2016, and in the second quarter we saw individuals in need of high-cost care represent an even larger share of our on-exchange population."

William E Aaronson, chair of Temple University's department of health services administration and policy, said Aetna could also be attempting to gain leverage over the government in negotiations over the Humana merger.

"The federal government has a lot at stake with the success of the Affordable Care Act. At the same time, these large insurance companies have a lot at stake in terms of the mergers that they've proposed," Aaronson said.

Losses on ACA plans have been widespread.

An Independence Blue Cross official said in the spring that in 2015 it experienced a significant increase in the use of health services by individual exchange members.

Brian Lobley, president of commercial and consumer markets at Independence, said Tuesday that IBC was evaluating the impact of Aetna's decision. Lobley said IBC remained committed to its members and to health-care reform.

Of IBC's 180,000 individual members, 70 percent have enrolled through Pennsylvania's federally facilitated marketplace, the company said.

"But as we have said, there are challenges that must be addressed to ensure the long-term stability of the individual market," Lobley said.

hbrubaker@phillynews.com215-854-4651@InqBrubaker