The National Institutes of Health “expects to admit a patient with exposure to the Ebola virus” later Thursday into its facility in Bethesda, Maryland, “for observation and to enroll in a clinical protocol,” the NIH said.

The patient is an American nurse who volunteered at an Ebola treatment unit in the West African nation of Sierra Leone.

The NIH hospital outside Washington is one of a handful in the United States specially equipped to treat patients with highly infectious diseases like Ebola.

The vast majority of the more than 18,000 confirmed and suspected cases, and the more than 6,500 deaths, in the latest Ebola outbreak have been in West Africa, according to the World Health Organization. And at more than 8,000 cases, Sierra Leone has had the most cases of any country.

Several people who have been treated at American hospitals were first diagnosed with the virus in the region. There have been some exceptions, like Liberian national Thomas Eric Duncan, who was diagnosed at a Dallas hospital, where he died.

One of the nurses who treated Duncan, Nina Pham, caught Ebola and underwent treatment at the National Institutes of Health facility in Maryland. The NIH declared her Ebola-free in late October.

In September, the same NIH facility admitted an unnamed American doctor who was exposed to Ebola while volunteering in Sierra Leone. But there was no indication that this doctor ever contracted the virus.