Contaminated man (2000)

In this science fiction thriller, David Whitman (William Hurt) is a chemist who lost his wife and child in a freak accident and is trying to rebuild his life on his own. While doing research, Whitman discovers a series of mysterious deaths that seem to follow in the path of Joseph Mueller (Peter Weller), a seemingly ordinary man who works as a security guard. Unknown to Mueller, his body carries a strange contaminant that's deadly to many people, and Whitman is desperate to find Mueller and stop him before he can cause more deaths.