WASHINGTON, Oct. 15 -- A second nurse in the U.S. state of Texas has tested positive for Ebola after taking a flight a day before she was ill, U.S. health officials said Wednesday, as President Barack Obama hurried to convene a Cabinet meeting to discuss the government's response to the deadly disease.

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.

Even 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. Both of the nurses provided care for 42- year-old Thomas Eric Duncan, the first Ebola patient diagnosed on American soil who had recently arrived from Liberia and died last Wednesday.

"At that point, that patient, as well as the rest of the healthcare team, were undergoing self-monitoring," he said, adding: "The second healthcare worker reported no symptoms and no fever. However, because at that point she was in a group of individuals known to have exposure to Ebola, she should not have traveled on a commercial flight."

He also noted that the woman found her temperature to be 99.5 ( 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.

"But we're putting into place extra margins of safety, and that 's why we're contacting everyone who was on that flight," said Frieden.

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."

He also said the second nurse with Ebola will be transported later in the day to Emory University Hospital in Atlanta, where other Ebola patients brought back from West Africa have been successfully treated.

With regard to the first nurse, Frieden said she is "in improved condition."

Meanwhile, U.S. President Barack Obama on Wednesday canceled a scheduled trip to New Jersey and Connecticut on the East Coast to hold a Cabinet meeting on Ebola, said the White House.

"The President's travel today to New Jersey and Connecticut has been postponed," the White House said in a statement. "Later this afternoon, the President will convene a meeting with cabinet agencies coordinating the government's Ebola response."

Obama was originally scheduled to speak at a Democratic Senatorial Campaign Committee event in New Jersey and then travel to Connecticut to attend a campaign rally with Dannel Malloy, a Democrat, who is also the governor of Connecticut.