The U.S. State Department on May 21 said that all American citizens and legal residents who have been in areas affected by the Ebola outbreak in Africa must go through a single airport in the United States when returning to the country.

All Americans and lawful permanent residents who have been in Congo, Uganda, or South Sudan within 21 days of arriving in the United States “must only enter through Washington Dulles International Airport (IAD) for enhanced screening,” the department said in an alert.

Federal authorities with the Department of Homeland Security and the Centers for Disease Control and Prevention will carry out the enhanced screening, officials said.

People should be prepared for flight changes or cancellations due to the development, according to the government.

Dulles is one of three airports serving the District of Columbia and its surrounding regions. Dulles is located in Northern Virginia, about 26 miles from the U.S. Capitol.

Ebola is a disease caused by orthoebolaviruses. It can cause symptoms such as fever, vomiting, and unexplained bleeding.

A meta-analysis of studies published May 20 and covering previous Ebola outbreaks in Africa found a mortality rate of 54 percent.

Most of the cases in the current outbreak so far have been in Congo, although two have been confirmed in neighboring Uganda.

An American doctor caring for patients at a hospital in Congo’s Ituri province, the epicenter of the outbreak, tested positive for Ebola over the weekend and has been flown to Germany for treatment.

“Before I was evacuated I was feeling really concerned I wasn’t going to make it. And now I’m cautiously optimistic,” Dr. Peter Stafford, the doctor, said in a statement released Thursday by Surge, a Christian organization with which he works.

Stafford’s children and his wife, also a doctor, are with him in a hospital in Berlin, officials said.

Acting CDC Director Dr. Jay Bhattacharya signed an order that outlined the rationale behind the move as “the serious risk posed by the introduction of Ebola disease into the United States by covered aliens.”

“This pause includes applications for immigrant visas as well as nonimmigrant visas for tourists, business travelers, students, exchange visitors, and all other nonimmigrant categories,“ the agency stated. ”Affected visa applicants have been notified.”

The State Department has also said that people should not travel to Congo, South Sudan, and Uganda due to the outbreak and rampant civil unrest.