Medical detective work will be the next big phase in the fight against Ebola when the United Nations deploys hundreds of health workers to identify chains of infection as the virus passes from person to person, top U.N. health workers said.

The health teams will travel to each district and region of Guinea, Sierra Leone and Liberia, the three countries at the center of the epidemic, to trace who each infected person has potentially contacted. The effort will run in parallel with measures to minimize the spread of infection, such as treating all Ebola patients in specialized centers and burying all victims safely.

But the second phase of the plan is to contain the virus by understanding its lines of transmission, said World Health Organization Director General Margaret Chan.