In the fight against terrorism, few stones are left unturned. Every day, patient data from a handful of emergency rooms is sent to the Indiana State Department of Health to be crunched and analyzed. An epidemiologist watches intently for upward trends in rashes, fevers and unexplained deaths. Or a sudden surge in over-the-counter drug sales. The practice -- called syndromic surveillance -- broke onto the public health scene immediately after the Sept. 11, 2001, terrorist attacks and later anthrax deaths. The surveillance method is widely viewed as a tool to detect a possible bioterrorism attack. Computers allow the instant sharing...