Former Centers for Disease Control and Prevention Director Robert Redfield warned on Wednesday that the Ebola outbreak spreading in central and eastern Africa could expand into three more countries and become a "very significant pandemic."

Redfield Warns Outbreak Could Spread Further

"I suspect this is going to become a very significant pandemic, probably going to leak into Tanzania, leak into southern Sudan, maybe leak into Rwanda," Redfield said on NewsNation's "Elizabeth Vargas Reports." "So, it's going to be very disruptive."

Most cases remain concentrated in the Democratic Republic of Congo and Uganda. The CDC said local health officials had reported 536 suspected cases, 105 probable cases, 34 confirmed cases and about 134 suspected deaths. The agency's latest situation update said the DRC and Uganda had reported 575 suspected cases, 51 confirmed cases and 148 suspected deaths as of May 21.

Late Detection Raises Public Health Concerns

Redfield said the outbreak had become a matter of "significant public health international concern" partly because authorities did not identify it quickly. He said he was not sure why the outbreak escaped early detection.

The former CDC chief said the outbreak is "moving very rapidly." The CDC said the current outbreak, caused by the Bundibugyo virus, marks Congo's 17th Ebola outbreak in the past 50 years. The country's most recent outbreak ended last December.

"Normally when we have these Ebola outbreaks, and I had three of them when I was CDC director, all of which were in the DRC, normally we recognize them when we have five, 10 cases, you know, at most," Redfield said. "This one really wasn't picked up until there was over 100 cases."

U.S. Screening Rules Tighten For Travelers

The former CDC chief's comments came after WHO chief Tedros Adhanom Ghebreyesus pushed back on Secretary of State Marco Rubio's claim that WHO was "a little late" in identifying the outbreak, saying WHO supports countries rather than replacing their surveillance systems.

The State Department said Thursday that U.S. citizens and lawful permanent residents who were in Congo, Uganda or South Sudan within 21 days of arriving in the United States must undergo enhanced CDC and Customs and Border Protection screening.