The search for people who may have been exposed to the deadly Ebola virus continued to widen Friday with Frontier Airlines and both federal and state officials reaching out to over 700 passengers and crew, following the diagnosis of a second Dallas nurse who took two commercial flights between Dallas and Cleveland — while possibly showing symptoms of the disease.

Nina Pham and Amber Vinson, both nurses who treated Thomas Eric Duncan at Texas Presbyterian Hospital before his death on Oct. 8, are in isolation at separate facilities following their diagnoses. But the Centers for Disease Control and Prevention is frantically working to trace those who may have had contact with them in an ever-widening circle of people potentially exposed to the disease which has killed more than 4,000 people in west Africa.

On Friday, sources told Fox News that all four U.S. Ebola patients— Pham, Vinson, NBC cameraman Ashoka Mukpo and an unnamed patient at Emory University Hospital—  were in "stable" condition.

So-called “contact tracing” involves tracking down everyone who came in direct contact with a confirmed Ebola patient and monitoring them for signs of illness for 21 days from the last day they came into contact with the Ebola patient. If any of those contacted develop fever or other Ebola symptoms, which can include vomiting and diarrhea, they are immediately isolated and tested while the CDC begins anew the process of tracking down all of their recent contacts.

With only two confirmed diagnoses, the number of people potentially exposed is manageable, but authorities caution that any subsequent confirmed cases could exponentially widen the circle. Pham appears to have had little contact with others prior to her diagnosis, but Vinson flew on two commercial domestic flights after possibly becoming symptomatic, and visited friends and relatives in Ohio. Those people are being sought for monitoring. And a lab worker from the hospital who was one of the original group of health care workers identified for monitoring is now aboard a Carnival Cruise Lines ship in the Caribbean, although she is quarantined and has not believed to have shown any symptoms.

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“She is deemed by the CDC to be very low risk,” Carnival said in a the statement. The passenger has been in isolation on the ship “in extreme abundance of caution and they are in close contact with the CDC, who has advised them at this time that the appropriate course of action is to keep the passenger in isolation on board.

Vinson flew from Dallas/Fort Worth to Cleveland on Oct. 10 and flew back to Dallas on Monday. Because she had a low-grade fever around the time of the second flight, the CDC has reached out to 132 fellow passengers on the Frontier Airlines flight. The airline is reaching out to approximately 750 additional passengers via email who flew on the same plane before it was disinfected on Oct. 13. According to a statement from Frontier, the CDC has no concerns that these passengers are at risk, however, if they have risks, they should contact local health authorities.

On Friday, Texas Governor Rick Perry said that health officials are actively monitoring eight people who had close contact with Vinson onboard the flight from Dallas to Cleveland. These eight passengers were in close proximity, within three feet, of Vinson.

Frontier took the plane out of service on Wednesday morning for cleaning and put two pilots and four flight attendants on a paid 21-day leave of absence as a precaution, the letter said, even though CDC guidance stated the crews were safe to fly.

At a press conference Wednesday morning, officials said the second health care worker was interviewed quickly to identify contacts or potential exposure.

At a press conference Thursday afternoon, officials in Summit County, Ohio, said that while in Ohio, Vinson intentionally kept her distance from family members and friends— not hugging or kissing anyone— even before she began feeling sick. The bridal shop she visited with her five friends has voluntarily self-quarantined itself and there are now eight local individuals under voluntary quarantine.

On Friday, Ohio officials announced that they are monitoring 16 contacts in Summit and Cuyahoga counties. All are healthy and they noted that those who are contacts do not have the disease and could have been exposed but not infected. None of the contacts have symptoms of Ebola. One person remains under voluntary quarantine.

A CDC doctor on the scene predicted that there will be no outbreaks of Ebola there and that "this is going to come under wraps."

Dallas County has been monitoring 48 close contacts of Duncan’s since his diagnosis on September 29. Four of Duncan’s family members were put under a control order and were legally quarantined on October 3 after refusing to comply with Dallas health official requests that they stay home. The family’s home was disinfected on October 4, at which time they were moved a private residence in a gated community that was offered by a volunteer.

“Those contacts have now passed more than two-thirds of their risk period. They have all passed more than 14 days. While it wouldn't be impossible that some of them would develop the disease, they have now passed through the highest risk period and it’s decreasingly likely that any of them will develop Ebola,” Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention (CDC) said in a press conference Tuesday.

A spokesperson for Dallas County Health & Human Services confirmed to FoxNews.com that the group of 48 are being monitored twice a day.

An additional group of 77 individuals came under monitoring after the first health care worker, Nina Pham, was diagnosed on Monday, including the second health care worker who was confirmed as infected on Tuesday evening, a CDC spokesperson confirmed with FoxNews.com.

As of Thursday, Dallas County Health & Human Services were monitoring a total of 135 contacts. Taking into account the individuals who were previously being monitored before Vinson’s diagnosis, an additional 10 contacts had been added to the county’s initial watch list.

“You can do the math,” Dallas County spokesperson Erikka Neroes told FoxNews.com.

Pham, who contracted the virus while caring for Duncan, is believed to have had only one contact while she was in an infectious state and that person is being monitored. In a press conference Wednesday,  Dr. David Lakey, commissioner for the Texas Department of Health said the contact was doing well and had no symptoms.

“That is a representation of what happens when you do active monitoring, when you do contact tracing, and when you encourage people to come in for care promptly,” Frieden said Tuesday.

Pham had been monitoring her own temperature and went to the hospital Friday night with a low fever. She was moved from Texas to the National Institutes of Health hospital in Bethesda, Maryland on Thursday. Vinson was moved to Emory University Hospital on Wednesday.

According to Dallas County Judge Clay Jenkins, the other health care workers who treated Duncan are employed but not working.

Notices handed out to Vinson’s neighbors advise them that "a health care worker who lives in your area has tested positive for Ebola."

Despite calls from lawmakers for a travel ban on flights to and from three African countries ravaged by Ebola to keep stricken passengers off America-bound planes, the White House said it's not a measure currently being considered.

"So far, no one with Ebola symptoms has entered this country," White House press secretary said. "So I recognize that you might describe that as a zero percent success rate, but to date, it's evident to me that we have a 100 percent success rate."

The disease has killed more than 4,000 people in West Africa, with most of the deaths coming in the nations of Liberia, Sierra Leone and Guinea.

Fox News's Nicole Kwan contributed to this report.