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.