A few dates to keep in mind.
Thomas Duncan was apparently infected when he helped a neighbor on September 15. Nine days later on September 24 he started showing symptoms of the Ebola and was admitted to the hospital on September 28. The first symptoms of Ebola show up between 2 and 21 days from infection, but most typically around 8 to 10 days. The window for patients exposed when Duncan was outside the hospital will expire on October 19, but we are past the typical time for symptoms to appear. Duncan died on October 8, the window for health care staff infected during Duncan's treatment will close on October 29. The time after infection when patients start to show symptoms follows a bell curve. The good news is that it gets less likely every day that we will find another civilian infected by Duncan before he was isolated.
Nina Pham was placed in isolation on October 10. She was directly involved in Duncan's care, but we don't know for certain exactly when she was infected. On October 31, the window for civilians exposed before she was isolated will close.
Amber Vinson was placed in isolation on October 14. She was also directly involved in treating Duncan. The window for civilians exposed before she was isolated will close on November 4. Amber was transferred to Emory in Atlanta on October 15, her case no longer poses a risk to workers at the Texas hospital.
There are reports that infection control measures used at Texas Health Presbyterian were lax. Two infected health care workers are the result. So far there is no indication that Ebola has spread beyond health care workers directly involved in treating Duncan. This makes sense if you understand the progression of the disease. There is less risk being around a patient in the early stages of the disease. Health care workers in Texas who are treating Nina Pham are still at risk. In hindsight, it would have been better to send her to Emory. But at this point, she is probably too fragile to survive the trip.
If additional cases are discovered, they should be sent to a hospital with special facilities like Emory.