In west africa the air is warm and moist. Resperiated droplets don't dry out and fall out of the air. In the cool dry air in the hospital... they dry and stay in the air. There is a reason almost all viruses thrive in winter. Coool Dry Air.
The fortunate thing is that Ebola dosn't particularly favor inffection of the air way If it did way more virus would become airborn. On the other hand I don't think the virus cares how it gets in. Also since nobody in his family appears to be sick... it really does appear you arn't to contageous till late in the illness. Some confort for the comunity but hell for the health care workers.