Caitlin Houston of Wallingford, CT, thought it was bad allergies when she started feeling sick last spring. In Las Vegas, Loleta Barrion had symptoms that at first felt like a cold or maybe the flu—crushing headaches, problems breathing—before realizing something more serious was going on. A laundry list of symptoms initially waylaid Zoe Kennedy of Stamford, CT, for three weeks, with her sense of smell never returning. And Christina Stanton of New York City says she had such low blood pressure that she couldn’t stand without fainting—with symptoms so severe, she ended up in the hospital, not once but twice.