The phone calls were part Big Brother, part benevolent parent. When a rare ice storm threatened New Orleans in January, some residents heard from a city official who had gained access to their private medical information. Kidney dialysis patients were advised to seek early treatment because clinics would be closing. Others who rely on breathing machines at home were told how to find help if the power went out.

Those warnings resulted from vast volumes of government data. For the first time, federal officials scoured Medicare health insurance claims to identify potentially vulnerable people and share their names with local public health authorities for outreach during emergencies and disaster drills.

The program is just one of a growing number of public and corporate efforts to take health information far beyond the doctor’s office, offering the promise of better care but also raising concerns about patient privacy.

In some cities, text messages remind parents to get their children vaccinated. Elsewhere, emergency medical services sift records to identify — sometimes to law enforcement officials — "frequent fliers" who take repeated, costly ambulance trips. In New Orleans, a health care information exchange notifies primary care physicians when their patients are admitted to hospitals, offers insurers the ability to sift the data for "high-cost users," and permits authorized individuals to "break the glass" in emergencies — viewing records of patients who have not previously given permission and cannot speak for themselves. And a federal program allows data sharing with public health officials to monitor "mental health conditions" and other illnesses in hazardous situations, like the Deepwater Horizon oil spill.

"There are a lot of sensitivities involved here," said Kristin Finne, a senior policy analyst at the Department of Health and Human Services. "When we started this idea," she said, referring to using Medicare data for disaster assistance, "there was a lot of ‘are you crazy?’" she added.

Finne noted that the program was painstakingly designed to comply with privacy laws.

Aspects of the Medicare program were tested in New Orleans; in Broome County, New York, which includes Binghamton; and in Arizona. The program was presented to state and local public health officials last month. "We are now moving to scale this really across the country," said Dr. Nicole Lurie, assistant health secretary for preparedness and response.

The health officials’ intention was to be more proactive in finding vulnerable people like those who suffered in disasters such as Hurricanes Katrina and Sandy. When government teams knocked on doors last year to verify the data and gauge reactions, nearly all the residents allowed them in. Only those who asked how they were found were told.

About a dozen advocates for people with disabilities who were briefed by officials generally expressed support.

Others find the program troubling, however well intentioned. "I think it’s invasive to use their information in this way," said Christy Dunaway, who works on emergency planning for the National Council on Independent Living, which supports disabled people living at home.

She and others said they were worried that identified individuals could be forced to evacuate to shelters that cannot accommodate people with disabilities, or that incomplete data could provide false assurances of government rescue.

For now, at least, federal officials have resolved not to identify people in "stigmatized groups" that might need help in emergencies, such as those with mental illnesses or intellectual disabilities, or those who are obese.

Dr. Karen DeSalvo, a former New Orleans health director who helped develop the Medicare pilot program and now leads the Office of the National Coordinator for Health InformationTechnology, said the program protected patient privacy and that its benefits outweighed its risks. "This is the next chapter of what good data can do for good purposes," she said. The federal government has spent more than $22 billion for the digitizing of health records.

"We are all going to have to, I’m hoping, come to some consensus with how we’re balancing privacy and security with the need to save somebody’s life," DeSalvo said.

The idea for the program began in Tuscaloosa, Alabama, after a tornado struck in April 2011. An ambulance rolled up to one of the houses left standing to take a woman to the hospital because she had run out of oxygen. "That’s kind of crazy, why can’t somebody bring her an oxygen tank?" Lurie recalled thinking after watching the scene.

She witnessed a similar phenomenon in New York after Hurricane Sandy. Patients who relied on medical equipment needed a place to plug it in before draining the batteries. Many crowded into emergency rooms, stressing the health care system. Others had no way to call for help. Eventually, emergency teams knocked on every door of darkened high-rises, because officials did not know where the people who needed assistance were.

"All of these people just came out of the woodwork," Lurie said one public health official told her after a disaster in New England.

"I started to seethe," Lurie said. "It’s your job to know who lives in your community." And if local officials did not, she added, it was the federal government’s responsibility to help.

Federal and state laws restrict the disclosure of medical data, so government lawyers defined a legal route for Medicare to transfer data on patients’ bills for medical equipment to public health authorities that have systems in place to protect patient privacy. They published a description of it in the Federal Register.

"Now every Medicare beneficiary at least theoretically is on notice that their information could be shared in this way," said Kevin Horahan, a lawyer for the Department of Health and Human Services.

New Orleans was the first test site. One day in June, with a pretend hurricane bearing down on the city, local officials received 611 names and addresses of residents who depended on oxygen equipment and ventilators. The next day, they dispatched police, fire and emergency services personnel, along with public health officials and credentialed citizen volunteers, to visit about a third of the homes and see how reliable the information was.

Finne, the health department official, led a team canvassing one of the poorest sections of New Orleans. "We went and knocked on doors and asked, ‘Does Mrs. Smith live here and have an oxygen concentrator?’" she said. Revelations of surveillance on American citizens by the National Security Agency had hit the news five days earlier. "It was one of those situations that you’re like, how are these people going to respond to us showing up?" she said. "Why is government showing up at my doorstep?"

A few residents refused to open their doors, but a vast majority were grateful, Finne said. The information was both accurate and revealing. In one neighborhood, not a single person with an electric breathing device had a backup battery in case of a power failure. More than half of those asked said they would need assistance in the event of a hurricane. However, only 15 of the 611 had enrolled in the city’s special needs registry, for those requiring assistance in an emergency. Results of the survey were set to be published online Thursday and in the July issue of the American Journal of Public Health.

A recent power failure affected René Brunét Jr., the 92-year-old owner of New Orleans’ oldest operating movie theater, the Prytania. He uses a ventilator to support his breathing. "I was frightened to death when I was without oxygen for so long," he said in an interview.

Because the data did not include his particular Medicare program, he was not visited by the public health teams last year. "Believe me, we would have welcomed it," said his wife, Muriel S. Brunét, 70.

Lurie’s office is developing a device that can alert family members or rescuers when batteries on medical equipment are low. The Department of Health and Human Services also plans to release an interactive Internet map this year indicating how many Medicare beneficiaries have wheelchairs and other medical equipment in various ZIP codes, in part to help health officials think about where to place shelters, stockpile supplies, and inform hospitals and power companies about potential needs. "Even that information is light-years ahead of what they have currently," Finne said.