The young girl came to the ER on March 17 with respiratory symptoms, generic enough not to raise any red flags. It took two days for her medical team to suspect measles, at which point they put her into isolation. But the measles virus is highly contagious. So anyone who sat in close enough proximity to her, or even sat in the same area hours later, could have been infected. At a hospital, that's particularly serious, as many people already have a compromised health status. In particular, the next patient to occupy the room the girl with measles was originally in was a 7-year-old boy with a terminal illness. His mother was horrified. For now, he seems to be in the clear, and the hospital sent letters as well to everyone who might've been exposed.