American Ebola patient at NIH hospital in Maryland

BETHESDA, Md. -- The National Institutes of Health said Friday that an American health care worker who contracted Ebola while volunteering in a Sierra Leone treatment unit had arrived safely at its hospital in Maryland.

The NIH said the patient arrived at the hospital in Bethesda, north of Washington, before 5 a.m. Friday and their condition was still being evaluated. The patient's name, age and gender have not been released.

Officials said the patient was transported to the United States in isolation on a chartered plane. The patient is the 11th person with Ebola to be treated in the U.S.

The NIH has one of the few containment facilities nationwide set up to treat Ebola patients. Previously, an American nurse was treated there after she contracted Ebola while caring for a patient in a Dallas hospital. The nurse, Nina Pham, survived and is Ebola-free.

Word of the latest U.S. Ebola patient came as the World Health Organization marked a grim milestone in the epidemic. It announced Thursday that the virus has now killed more than 10,000 people since the outbreak began last year. Almost all of the victims have been in the three West African nations of Guinea, Liberia and Sierra Leone.

WHO reported last week that Ebola remains "widespread" in Sierra Leone and more cases are still occurring in Guinea. However, Liberia has been making strides in controlling the disease and released its last known Ebola patient from the hospital on March 5.