The Hades Factor by Robert Ludlum
A teenage girl in Atlanta, an Army major in California, and a homeless man in Boston all die suddenly and painfully from the devastating effects of an unknown virus. Lt. Col. Jonathan Smith, a USAMRID doctor is assigned to solve the mystery of the virus' abrupt appearance. As the death count rapidly mounts by the thousands Smith barely survives a series of well-orchestrated attempts made on his life. Smith finds evidence that suggests that someone out there has the virus, and the pandemic that threatens hundreds of millions of lives is no accident. A very well read adrenaline filled action yarn.