Americans seeking to return home from the Ebola-stricken Democratic Republic of Congo (DRC) will be prevented from boarding flights to the United States under new restrictions. U.S. citizens and non-citizens who have been in the DRC within the past 21 days must now wait in a third nation for that period before entering the U.S.

This measure comes as the U.S. Department of State issued a 'Level 4: Do Not Travel' advisory for the DRC, citing health risks, crime, unrest, terrorism, and kidnapping. The advisory specifically mentions the Ebola outbreak as a reason for the heightened travel warning.

Travelers who have been in the DRC within 21 days of their intended flight to the U.S. will be denied boarding on commercial flights. The Centers for Disease Control and Prevention (CDC) stated that American citizens departing the DRC may be subject to a "DO NOT BOARD" order and are able to return to the United States 21 days after leaving the country.

Previously, U.S. citizens traveling from the DRC were permitted to return to the U.S. if they arrived at one of four designated airports for enhanced screening: Washington-Dulles International Airport in Virginia, Hartsfield-Jackson Atlanta International Airport in Georgia, George Bush Intercontinental Airport in Texas, and John F. Kennedy International Airport in New York.

The new restrictions were announced shortly after a second American citizen, a humanitarian worker in the DRC, tested positive for Ebola and was flown to Germany for treatment. An American doctor in the DRC who previously tested positive for the virus also recovered after being treated in Germany.

The current Ebola outbreak in the DRC is described as the fastest-growing on record, with nearly 2,000 people infected and 719 deaths attributed to it, according to the Africa Centres for Disease Control. The outbreak is caused by the Bundibugyo strain, which has a mortality rate of up to 50 percent and for which no vaccine or treatment exists.

While the CDC maintains that the risk to the general U.S. public is low, it urges travelers to avoid areas with sick individuals. Cases have also been reported in neighboring Uganda and South Sudan.

This is the 17th Ebola outbreak in the DRC since the virus was first discovered there in 1976. The most severe Ebola outbreak occurred in West Africa from 2014 to 2016, resulting in over 28,600 cases and 11,000 deaths.