As others have said, shut down the travel from these nations. Just read last night a case in Sierra Leona close to Guinea caused them to shut the borders.
The problem with all this effort is it may catch some but others can get in by going through other airports. And at the airports being checked, Duncan would have likely gotten through if they are just screening on temperature because he probably wasn't sick yet and we know he lied.
Duncan's family haven't heard anything, you'd expect them to be more contaminated than that medical worker; however the virus probably keeps multiplying until your whole body is full of the stuff, think they call it "load".
Maybe his family all already had it and are immune ...
No one comes here who had been in the affected countries within the last 21 or 28 days. That takes care of connecting flights through Europe. I'm surprised Brussels hasn't closed itself off--most of the infected people have come through that airport.