BETHESDA, Md. – An American nurse who was exposed to the Ebola virus while volunteering in Sierra Leone is being admitted to the National Institutes of Health near Washington, D.C.

The NIH says in a statement that the nurse was expected to be admitted to the Bethesda, Maryland, facility on Thursday. The NIH says the nurse has not tested positive for the deadly virus. The nurse’s identity was not released.

An NIH spokeswoman says the nurse will be taken to a special unit designed to isolate transmissible diseases.

The hospital previously helped treat a Dallas nurse infected while caring for Thomas Eric Duncan, a Liberian man who fell ill with Ebola shortly after arriving in the U.S. and later died. The nurse, Nina Pham, survived and is Ebola-free.