Officials are investigating a potential case of Ebola at the Pentagon after a woman on a tour bus became sick. The woman, who recently arrived from Africa, began vomiting and was rushed by ambulance to Virginia Hospital Center in Arlington.

A hazmat team was called out of “a complete abundance of caution,” Pentagon Force Protection Agency spokesman Chris Layman told 

A large portion of the Pentagon south parking lot has been cordoned off with crime tape, and police are telling those who don’t work at the Pentagon to avoid the immediate area. The potential threat comes as officials are struggling to reassure the American public that the Ebola outbreak that has killed more than 4,400 people in West Africa will not erupt on U.S. soil.

A Liberian man who traveled to Dallas, Thomas Duncan, became the first person in the U.S. to die from Ebola earlier this month. Two nurses who treated him, Nina Pham and Amber Joy Vinson, contracted the deadly virus from him and are now being treated.

Pham, 26, was transported by flight from the Dallas hospital where she has been receiving treatment for the virus this week to a National Institutes of Health facility in Maryland, officials said Thursday. Vinson, 29, was transferred Wednesday to Emory in Atlanta.

Some 75 health care workers being monitored for Ebola after treating Duncan have been told to stay out of public places and avoid public transportation, officials said Thursday. The voluntary agreement with the workers from Texas Health Presbyterian Hospital comes after Vinson took a round-trip flight from Texas to Ohio before testing positive for Ebola.

Dr. Daniel Varga, chief clinical officer and senior vice president of Texas Health Resources, said there was no Ebola training for staff before Duncan was admitted.