"We're going to make sure that something like this is not repeated," Obama spoke after meeting with top Cabinet officials on the government's response to Ebola.

"And we are monitoring, supervising, overseeing in a much more aggressive way exactly what's taken place in Dallas initially, and making sure that the lessons learned are then transmitted to hospitals and clinics all across the country."The nurse, identified as Amber Joy Vinson in the U.S. media, reported to a Dallas hospital with a low-grade fever and was isolated Tuesday morning. A preliminary test conducted by a Texas state laboratory showed she contracted Ebola.

more aggressiveEven more surprising, she had taken a Frontier Airlines flight from Cleveland, Ohio to Dallas/Fort Worth on Oct. 13, the day before she reported symptoms.

"This second health care worker case is very concerning," Director of the U.S. Centers for Disease Control and Prevention Tom Frieden told a teleconference.

He said the patient traveled to Ohio before it was known that the first nurse was ill and at the moment the healthcare team that provided care for 42-year-old Thomas Eric Duncan, a Liberian, was undergoing self-monitoring.

Duncan became the first person diagnosed with Ebola on American soil on Sept. 30. He arrived in the U.S. from Liberia on Sept. 20 and died Oct. 8.

Frieden also noted that the woman found her temperature was 99. 5 Fahrenheit (37.5 degrees Celsius) before she traveled Monday. It did not meet the fever threshold of 100.4 (38 degrees Celsius), but it did underscore the nurse "should not have traveled, should not have been allowed to travel" given her recent exposure to an Ebola patient, the CDC chief said.

He insisted that there was an "extremely low likelihood" that the 132 passengers on the Frontier Airlines flight would have been exposed because the nurse did not have nausea or vomiting symptoms at that time.

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.