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He also said their investigations "increasingly suggest" that the three days following patient Duncan's hospitalization on Sept. 28 appear to be the highest risk period for Ebola exposure.
"These two health care workers both worked on those days and both had extensive contact with the patient when the patient had extensive production of body fluids because of vomiting and diarrhea."
The second nurse with Ebola will be transported to Emory University Hospital in Atlanta, where other Ebola patients brought back from West Africa have been successfully treated, while the first nurse is "in improved condition," Frieden added.
In response to the infection in nurses, Obama acknowledged that "a lot of non-specialized hospitals and clinics don't have that much experience dealing with" Ebola.
But he emphasized that the likelihood of a widespread Ebola outbreak in the United States was "very, very low," saying he is " absolutely confident" that the U.S. can prevent a serious outbreak of the disease.
Obama also said the fact that the two nurses have gotten sick highlights the importance of the international response to the Ebola epidemic in West Africa.
"It is very important for us to understand that the investment we make in helping Liberia, Sierra Leone, and Guinea deal with this problem is an investment in our own public health," he said.
"It is also probably the single most important thing that we can do to prevent a more serious Ebola outbreak in this country is making sure that we get what is a raging epidemic right now in West Africa under control."
Obama canceled his scheduled campaign trip to New Jersey and Connecticut on the East Coast to convene the meeting.