UnitedHealth Group Inc.'s stock has been on a two-week surge, hitting an all-time high for the first time earlier this month and continuing to climb even higher.

Shares of the Minnetonka-based insurance company finished up 2.5 percent, to $79.96, on Wednesday, even as the broader market sagged because of worries about the Federal Reserve's intentions concerning interest rates.

There's "improving sentiment" for UnitedHealth along with its peers in the broader health sector, including WellPoint, Humana, Cigna and Aetna, said Thrivent Financial analyst David Heupel.

Enthusiasm stems from several factors ranging from the weather to Medicare Advantage rates to improved enrollment on health care exchanges, he said.

Insurers breathed a collective sigh of relief in late February when the Obama administration issued preliminary Medicare Advantage rates that were cut by 1.9 percent, not nearly as bad as expected. And as weather improves, more people will be making it to the doctor's office.

"January was pretty ugly because most people didn't like the fourth quarter," Heupel said. "And we've had some days that, for a lot of various reasons, have picked the group up."

"Let's face it," he added. "People don't want to go to the doctor when it's 20 below or there's 20 inches of snow."

Rising enrollment numbers also are fueling the burst, Heupel said. The federal government reported earlier this week that 5 million Americans have enrolled in health plans through new federal and state-based insurance exchanges. UnitedHealth stands to gain from states that have expanded Medicaid.

But the wariness over the rollout of the exchanges and the Affordable Care Act continues to temper enthusiasm.

"If we find out that no one is making money on these new customers, or maybe even losing money, that'll sour opinion," Heupel said.

WellPoint is hosting its analysts day on Friday, and some analysts are expecting an upbeat report. Its shares were up 1.37 percent to $99.05 on Wednesday.

Humana was up 3.1 percent to $116.96; Cigna was up 3.3 percent to $80.28.

Jackie Crosby • 612-673-7335