Isolating symptomatic patients is certainly effective, but it will not work as a proactive strategy of containment. By that point, a carrier may have already infected dozens of people. Even when surveillance is well deployed, the collateral costs associated with it are forbidding. Between July 31 and mid-September, New York City’s health department received 57 calls reporting suspected infections based on fevers. Of these, only six merited further testing. Three cases were caused by malaria and one by anaplasmosis; two were of unknown causes. Ebola was not found in any of the cases. There is a fourth strategy, although it...