He may or may not have known the landlord's daughter had Ebola. She was pregnant, and there have been some reports that the rest of the family thought she was hemorraging as a result of her pregnancy (remember, prenatal care in Liberia is.....not like it is here, so maternal mortality rates are higher).
As for the rest of your comment, I believe he had applied for a visa well before he was (knowingly or not) exposed to Ebola. It takes more than "several days" to get a US visa coming from Liberia.
Turned away from a hospital for lack of space in its Ebola treatment ward, the family said it took Ms. Williams back home in the evening, and that she died hours later, around 3 a.m.
Mr. Duncan, who was a family friend and also a tenant in a house owned by the Williams family, rode in the taxi in the front passenger seat while Ms. Williams, her father and her brother, Sonny Boy, shared the back seat, her parents said. Mr. Duncan then helped carry Ms. Williams, who was no longer able to walk, back to the family home that evening, neighbors said.
http://www.nytimes.com/2014/10/02/world/africa/ebola-victim-texas-thomas-eric-duncan.html?_r=0
http://www.freerepublic.com/focus/f-news/3210086/posts