Updated at 12:30 p.m. ET.

An American health care worker who contracted Ebola while volunteering in Sierra Leone is now receiving care at the National Institutes of Health Clinical Center in Maryland. The patient's condition is serious, the NIH says.

The patient is the second to be treated for Ebola at the Bethesda facility, which previously cared for — and eventually released — Nina Pham, a nurse who contracted Ebola in Dallas. The hospital has also monitored two patients who were seen as being at high risk of having the deadly disease. They were later released.

NPR's Richard Harris reports:

"The medical worker was flown back to the United States in a private jet and admitted to an isolation ward that's designed to treat highly infectious patients. NIH is not releasing any information about the patient."The aid group Partners in Health said the clinician was one of 100 expatriates it had deployed in West Africa and the first to contract the disease."Also this week, Britain airlifted a medical worker back to the UK from West Africa after that person became infected with Ebola. The World Health Organization says more than 10,000 people have died of Ebola in West Africa. The epidemic is on the wane, but is not yet fully under control."Copyright 2016 NPR. To see more, visit http://www.npr.org/.