Incubation period is from one to three weeks from what I understand. This woman showed serious symptoms today.
Probably several thousand could easily have come into contact with her directly or indirectly by this time. And they in turn came in contact with...
Wow - I need a calculator.
Ebola is only contagious once symptoms appear. Also, Ebola is not spread through aerosols, but by direct contact with infected fluids, including droplets. So, if this woman vomited or had diarrhea and droplets got onto people, there could be a problem. Otherwise, not.
Personally, I think it is silly to announce every potential case being tested for Ebola. There are many other diseases in Africa, including other hemorrhagic fevers. If a case pops positive, *then* I want to see the results.