In a 2013 paper, Dr. Harlan Krumholz, a professor of medicine and public health at Yale School of Medicine, described a syndrome that emerges in the days and weeks after a hospital stay: "Physiologic systems are impaired, reserves are depleted, and the body cannot effectively avoid or mitigate health threats." He called this period of vulnerability "post-hospital syndrome." The syndrome was identified as a result of new Medicare rules that hold hospitals responsible for re-admissions within 30 days after discharge. When health systems began studying patients who returned to the hospital soon after discharge, two critical facts emerged. First, the problem is common and widespread, occurring after nearly one in five hospitalizations of patients on Medicare.