COLUMBIA, S.C. — Tim Liszewski awoke last Saturday and padded down the steps at his Columbia home, hoping the headaches and fever that had bothered him would finally go away.It had been a rough and confounding week for Liszewski, a 60-year-old activist who didn’t get sick very often. After returning from a conference in the Midwest, he’d been unable to shake the illness that was keeping him away from his work at a grassroots political organization.Then, sometime after descending the stairs the morning of March 28 to check his computer, he collapsed. A few hours later, his fiancee found Liszews...