It started with a cough, an autumn hack that refused to go away. Then came the fevers. They bathed and chilled the skinny frame of Oswaldo Juarez, a 19-year-old Peruvian visiting to study English. His lungs clattered, his chest tightened and he ached with every gasp. During a wheezing fit at 4 a.m., Juarez felt a warm knot rise from his throat. He ran to the bathroom sink and spewed a mouthful of blood.