in late april, 2009, a 22-year old man suddenly experienced headache, myalgia, malaise, dry cough, and fever. he basically felt lousy. after a couple of days, he had a sore throat, his cough had worsened, he started to feel nauseated, and he began vomiting. several of his friends had experienced similar symptoms during the previous 2 weeks. a rapid antigen test was positive for influenza a.