Story highlights

American was flown from Africa to Maryland hospital

NIH has one of only four U.S. hospital biocontainment units

CNN  — 

An American health care worker who came down with Ebola while volunteering in West Africa arrived Friday at a National Institutes of Health hospital in Maryland for treatment, the NIH said.

A chartered aircraft flew the patient to the United States from Sierra Leone, where the person tested positive for the deadly hemorrhagic fever while volunteering at an Ebola treatment center, the NIH said.

The patient was in serious condition Friday, the NIH said. Details about the patient’s identity weren’t released.

The patient is the second with Ebola admitted to the NIH hospital. Nina Pham, a nurse at Texas Health Presbyterian Hospital Dallas, was admitted to NIH in October after she contracted the disease while treating Liberian national Thomas Eric Duncan. Pham recovered and was released free of disease. Duncan died.

Nurse who contracted Ebola sues hospital company

NIH is one of only four hospitals in the United States that have biocontainment units and has been practicing for years to treat a highly infectious disease such as Ebola.

More than 10,000 people have died in a West Africa epidemic of Ebola that dates back to December 2013, according to the World Health Organization. Most of the deaths have been in the countries of Guinea, Liberia and Sierra Leone.

Ebola is spread by direct contact with the bodily fluids of an infected person.

CNN’s Athena Jones and John Newsome contributed to this report.