WASHINGTON — The United States is tightening health screening protocols for international travel, implementing a new certification mandate designed to prevent the potential spread of Ebola.

According to a memo reviewed by Reuters, the U.S. Centers for Disease Control and Prevention (CDC) will require all air passengers traveling from foreign countries to the United States to formally attest that they have not visited the Democratic Republic of Congo (DRC) within the preceding 21 days.

The requirement addresses public health concerns linked to Ebola risks in the region. Previously, federal health rules outright barred travelers—including U.S. citizens and nationals—who had been in the DRC within a 21-day window from boarding commercial flights bound for the United States.