evidence: Scientists announced Monday that they may have solved one of history's biggest biomedical mysteries—why the deadly 1918 "Spanish flu" pandemic, which killed perhaps 50 million people worldwide, largely targeted healthy young adults. (Related: "How Flu Viruses Attack.") [...] Instead, people aged 18 to 29 died in droves during the outbreak, which killed about 1 in 200 of victims. [...] The overall message of the study is a hopeful one, say the researchers, because the bacterial pneumonia secondary to the 1918 flu that killed most of its victims is treatable with modern antibiotics.