American woman infected with Ebola arrives in U.S.

[Breaking news update, posted at 1:03 p.m. ET]

Nancy Writebol, the missionary infected with Ebola in Liberia, has arrived at Atlanta's Emory University Hospital. She was taken on a stretcher from an ambulance into the building.

[Earlier version, posted at 12:05 p.m. ET]

(CNN) -- While international health workers scramble to contain the deadliest Ebola outbreak in history, an American woman infected with the virus in Africa has arrived back in the United States -- making her only the second human Ebola patient ever in the country.

A specially equipped air ambulance delivered missionary Nancy Writebol to Georgia's Dobbins Air Reserve Base late Tuesday morning, having left Liberia earlier in the day. She will be taken to Atlanta's Emory University Hospital, where the other American Ebola patient, Dr. Kent Brantly, also is being treated.

Writebol and Brantly were caring for Ebola patients in Liberia last month when they became sick, and the same plane brought Brantly from Liberia to Georgia on Saturday.

Emory is just blocks from the Centers for Disease Control and Prevention, which helped Emory design an isolation unit -- one of four of its kind in the United States designed to optimize care for those with highly infectious diseases.

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"We're just grateful and very cautiously optimistic about how she's doing right now," Bruce Johnson, president of SIM USA, a Christian mission group Writebol is affiliated with, told CNN's "Erin Burnett OutFront" Monday night.

Though there is no proven treatment or vaccine for Ebola, both Brantly and Writebol were recently given a experimental, U.S.-manufactured drug in Liberia while they were awaiting evacuation to the United States. Both have since shown significant improvement, sources said on condition of anonymity.

What the inside of the evacuation plane looks like

But the gruesome disease that can torment victims with profuse vomiting, uncontrollable bleeding and organ failure still is ravaging West Africa. Ebola is believed to have infected 1,603 people in Guinea, Liberia, Sierra Leone and Nigeria, killing 887 of them as of Friday, the World Health Organization said.