ST. PETERSBURG — Charlene Lake thought she got a decent deal through the Affordable Care Act marketplace: a Humana HMO that included a family doctor a few miles from her home.

Five months later, Lake wonders if she can even use the insurance she bought.

Her plan's dominant health care provider, JSA Medical Group, recently announced that it would take no new patients covered by Humana's exchange HMOs at least until fall. That leaves Lake no choice but to use the community health centers left in her plan's network, rather than the traditional physician's practice on which she planned.

She has company. Humana is scrambling to add 100 doctors to its Tampa Bay network after it enrolled three times more people in marketplace plans than it anticipated.

But aside from first-year fumbles, the case also shows the downside of limiting consumer choice of physicians through what is known as narrow networks.

Or, in Lake's case, a network so narrow it barely exists.

"You can't make people sign up for a health care plan and then not have a doctor," said Lake, a St. Petersburg antiques dealer who is in her 50s.

Narrow networks of hospitals and physicians help insurers maintain profitability while holding down premiums and complying with ACA rules. Insurers have more leverage on medical prices when dealing with a smaller group of doctors and hospitals.

To the disappointment of those who pushed for a national health care system that would extend the federal Medicare system to everyone, the ACA keeps private insurers in the mix, which must make profits to stay afloat. But the law makes that more difficult by forbidding them from charging much higher prices to people with pre-existing conditions, or even denying them coverage. Crafting narrow networks is a tool that insurers use.

Nationwide, about 70 percent of the lowest-priced plans sold on the exchanges are considered to have narrow networks, according to a study by industry consultant McKinsey & Co. And they've caused problems. In California, for instance, insurance giant Anthem Blue Cross faces multiple consumer lawsuits over its use of narrow networks, with some policyholders saying the company had misled people with inaccurate provider lists.

Humana isn't the only Florida provider with network issues; Florida Blue consumers in South Florida told the Miami Herald they had problems getting doctors listed in their directories to accept their plans.

In the Tampa Bay area, Humana put most of its primary care business into the hands of JSA, a major physicians group that has long handled the insurer's Medicare Advantage customers. JSA has nearly 165 affiliated and employed physicians in the region.

Humana also added community health centers to its network. These nonprofit clinics offer the same services as traditional doctors' offices but also treat the uninsured, who pay based on their income.

Humana's online directory appears to offer plenty of choices. Last week, HMO customers in St. Petersburg had their choice of around 120 primary-care doctors within a 15-mile radius of downtown. But nearly all of those listings are JSA doctors, except for several community health centers and their doctors, listed separately, plus a Largo practice.

The insurer declined to say how many Tampa Bay residents it enrolled or how many of its members are affected by JSA's decision. Humana spokesman Mitch Lubitz said the number of exchange enrollees was three times higher than Humana had projected.

Because of that, in addition to its plan to add 100 doctors, the insurer added more hospitals to its network, including BayCare facilities and Bayfront Health Dade City.

JSA, which is owned by Denver health giant DaVita, confirmed it will not see new Humana HMO patients at least until fall. JSA president Lorie Glisson said it had served almost twice as many Humana exchange patients as it had expected in the Tampa Bay area.

"As a result of the strain placed on our existing clinics, and our desire to ensure the highest quality patient care, we have requested that Humana identify other available providers to deliver care for some of these new (HMO) patients," Glisson said in a statement.

Asked if the medical group was accepting new patients with other insurance plans, a spokesman said only that JSA was "welcoming as many patients as we can."

In Pasco County, Premier Community Health Center is the only provider for Humana exchange patients, said Cheryl Pollock, Premier's business development director.

"We're almost a monopoly at this point," she said. And that's not a good thing for Premier.

Though the center appreciated the new patients, many of them have not seen a doctor in years and have multiple problems they want addressed in their first visit, she said. In addition, Humana requires lengthy approvals for routine procedures and referrals.

Gary Claxton, a vice president with Kaiser Family Foundation, said narrow networks were around long before the ACA. The Humana-JSA dilemma sounded to him like a result of first-year miscalculations.

Few insurers or policy analysts thought so many Floridians would sign up for ACA insurance, given state leaders' refusal to participate in the exchanges. Yet nearly a million did enroll. And physicians were reluctant to jump into an uncertain market.

"It's not surprising that they didn't quite get it right," Claxton said. "To me, this is something that will work its way out after a few years."

But for now, Lake, the St. Petersburg resident, is stuck. She wonders why she's even considered a new patient since she saw a JSA doctor in May. When she called his office recently, the staff told her it was JSA's decision to drop her, not the doctor's.

She tried four times one day last week to reach a health center in her network on the campus of Bayfront Health St. Petersburg. No one answered the phone.

"This is a complete mess," she said. "They took away my doctor who I had gotten in to see within a few days because they claimed the patient load was too much and replaced him with an office that doesn't even answer their phone."

Other Humana exchange customers say they've noticed cancellations by JSA physicians. James Trizis, a 52-year-old Clearwater diner owner, said JSA recently rescheduled a September checkup for April.

Trizis, who has a heart condition, said he worries that preventative care — a key part of the ACA — will get short shrift.

"My primary care for me and my family is going to be the emergency room," he said.

Contact Jodie Tillman at jtillman@tampabay.com or (813) 226-3374. Follow @JTillmanTimes.