An American health care worker who contracted the Ebola virus as a volunteer in Sierra Leone arrived safely at the National Institutes of Health Clinical Center's Special Clinical Studies Unit in Maryland shortly before 5 a.m. EDT Friday. A private-charter medevac aircraft flew the patient in isolation from West Africa. 

The NIH said in a statement that the patient's condition was still being assessed. NIH would not release further details about the individual, but the New York Times has reported that the patient was part of the U.S. medical aid organization Partners In Health, which, until now, had yet to report a case of Ebola among its workers. The NIH did not disclose the patient's name or gender.

The Special Clinical Studies Unit is designed specifically for high-risk cases such as this one, with sophisticated isolation abilities and staff who are specialists in critical care and in treatment of infectious diseases. This is the second confirmed Ebola patient to be admitted to the NIH Clinical Center, which is one of few medical facilities in the U.S. with the capacity to handle Ebola cases, the Associated Press reported. The first patient was treated successfully. Two others who were exposed to Ebola were also admitted to the center after being exposed to the virus but eventually tested negative.

Ten other Ebola patients have been treated in the United States. Most of them tested positive for the virus after traveling outside the U.S, and two of them died. "NIH is taking every precaution to ensure the safety of our patients, NIH staff, and the public," the institute said in its statement Friday.

The health care worker being treated in Maryland was the second to be flown home from Sierra Leone this week after contracting Ebola. A British military nurse who tested positive for the virus was flown back from the West African country Thursday, along with two of the four colleagues who had come into close contact with her but were not diagnosed as having Ebola. The other two were flown back to Britain early Friday and are being monitored. More than 10,000 people have died in the West Africa Ebola outbreak, the origins of which have been traced to December 2013, with the first cases reported in March 2014. Liberia, Guinea and Sierra Leone have been the countries hardest hit by the virus.