A flight bound for Detroit was diverted to Canada overnight after a passenger from the Democratic Republic of Congo (DRC) “incorrectly” boarded the plane amid restrictions in place over the Ebola outbreak, U.S. officials say.

A U.S. Customs and Border Protection spokesperson said in a statement that the agency “took decisive action” to divert Air France Flight 378, which departed Paris on Wednesday evening.

“Air France boarded a passenger from the Democratic Republic of Congo in error on a flight to the United States,” the statement said. “Due to entry restrictions put in place to reduce the risk of the Ebola virus, the passenger should not have boarded the plane.”

The U.S. Centers for Disease Control and Prevention has temporarily banned travel to the United States for people without American passports who have been in DRC, South Sudan or Uganda in the past three weeks.

The CDC confirmed that an American doctor working in DRC, identified as Peter Stafford, had tested positive for Ebola and was taken to Germany for treatment. Six other U.S. citizens have been exposed.

A Christian missionary group that Stafford works with reported on Thursday that he was “critically ill but not acutely deteriorating.” Stafford’s wife, who is also a doctor, and their four children are asymptomatic and quarantining in Germany as a precaution, the group said.

According to the World Health Organization, there have been more than 500 reported Ebola cases and more than 130 deaths as of May 18.

Earlier this week, Tedros Adhanom Ghebreyesus, WHO director-general, said he was “deeply concerned about the scale and speed” of the outbreak and declared it a public health emergency.

While the risk of a global outbreak remains low, the risk of it spreading nationally and regionally in DRC and Uganda is high, he added.

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