Updated

Health officials on Saturday were preparing to receive an American stricken with the Ebola virus while in Africa, marking the first time a patient with the deadly disease will be treated on U.S. soil.

One of the Americans is expected to arrive at a U.S. military base Saturday afternoon on a small private jet outfitted with a special, portable tent designed for transporting patients with highly infectious diseases that can only hold one person at a time. It was not immediately clear when the second patient would arrive.

The U.S. State Department and the Centers for Disease Control and Prevention are helping to arrange the evacuation.

"The safety and security of U.S. citizens is our paramount concern," said the State Department spokeswoman Marie Harf, in a statement released Friday morning. "Every precaution is being taken to move the patients safely and securely."

The two Americans - Dr. Kent Brantly and Nancy Writebol - are in serious condition and were still in Liberia on Friday, said the charity Samaritan's Purse.

Brantly, who works for Samaritan's Purse, treated Ebola patients at a Liberia hospital. Writebol also worked at the hospital for another U.S. mission group called SIM.

The Americans will be treated at Atlanta's Emory University Hospital, which has a special isolation unit.

In a press conference Friday afternoon, Emory’s Dr. Bruce Ribner, said the facility had been informed that two patients were coming to the facility; one in a few days, the next a few days after that. Ribner, a professor of infectious diseases who oversees the isolation unit, was told that the patients were safe for transport.

The patients will be placed in the hospital’s containment unit, which is discrete from the rest of the hospital. This will be the first time a patient with the Ebola virus will be treated in the U.S. and Emory is taking safety precautions seriously, Ribner said.

“From the time the air ambulance arrives in the metro Atlanta area, up to and including being hospitalized at Emory University Hospital, we have taken every precaution we know and that our colleagues at the CDC know to ensure no spread of this pathogen,” he said.

The patients will be under the care of four infectious disease physicians, including Ribner. At any given time, there will be two nurses available for each patient and subspecialists are available if more care is needed. Ribner noted that, at this time, they do not know how long the patients will be under their care, as degrees of illness complications affect patients’ ability to stabilize and recover.

“Based on our experience, policies, procedures, I have no concern about either my personal health or the health of the other health care workers,” Ribner said.

Ribner repeatedly emphasized that Emory is not concerned about potential spread of the disease.

“We are talking about a viral pathogen that does not have some exotic mode of transmission. [Ebola has] a mode of transmission we are well familiar with with other viruses,” he said. “We have special policies and procedures from the transport side and health care side in the hospital to ensure there is a safe environment to take care of these patients. [I] don’t believe there’s any likelihood at all there would be any secondary [transmission] at all of these patients coming to us.”

The Emory isolation unit is one of about four around the country for testing and treating people who may have been exposed to very dangerous viruses, said Dr. Eileen Farnon, a Temple University doctor who formerly worked at the CDC and led teams investigating past Ebola outbreaks in Africa.

“It is physically separate from other patient areas and has unique equipment and infrastructure that provide an extraordinarily high level of clinical isolation,” CDC director, Dr. Tom Frieden told ABC News.

The Pentagon said said Friday that a chartered flight with the patients will land at Dobbins Air Base in Marietta, Ga. sometime over the coming days, according spokesman, Rear Admiral John Kirby.

While he did not give a specific time of arrival, Kirby said no military personnel would be involved and that the U.S. State Department had requested use of the runway for security purposes.

A statement from SIM Missionary Friday said Writebol’s husband, David, will stay close by as plans are made to bring his wife back to the U.S. for treatment. But with her condition, he will only be able to visit his wife through a window or dressed in a haz-mat suit.

No others from SIM who are returning to the U.S. have tested positive for Ebola.

“We are so heartened that Nancy is in stable condition and that plans are underway to bring her back to the U.S.,” said Bruce Johnson, president of SIM USA in the release. “We are grateful for the help and support of the U.S. State Department in this endeavor. As believers in the power of prayer, we covet the prayers of people around the world, not only for Nancy and Kent, but also for all those fighting this brutal virus.”

Although nonessential SIM personnel are leaving the country, SIM is sending in another of its doctors to help with the treatment of Ebola patients at its ELWA treatment center in Monrovia.  SIM currently has two doctors caring for Writebol and Brantly, and its Liberian staff is still engaged in the region.

According to Dr. Jean Patterson, chair of the department of virology and immunology at Texas Biomedical Research Institute in San Antonio— whose lab has worked with both government agencies and medical institutions to develop therapies and vaccines against pathogens that can cause lethal outbreaks since 2001— there’s no cause of concern for the spread of Ebola in the U.S. She added that exhaustion and a resource-diminished environment in Liberia could be the cause behind the transmission of the virus from infected patients to health workers like Brantly and Writebol.

“…You don’t have all the infrastructure we have here in the U.S., it’s very difficult to maintain all the standards,” she told FoxNews.com. “There have been scenarios that were developed by the Army many years ago with the possibility of an American citizen developing a deadly disease.”

Ebola is a highly fatal disease, but it does not spread easily from person to person, according to the CDC. The virus is most often transmitted through bodily fluids, meaning that the highest risk for becoming infected lies with the medical staff treating the patients.

The current outbreak in the West African countries of Liberia, Guinea and Sierra Leone has killed more than 700 people.

The Associated Press contributed to this report.