By Alexandra Sifferlin
September 2, 2014

The window of opportunity to stop the Ebola outbreak in West Africa is “closing quickly,” a top health official said Tuesday.

“The number of cases is so large, the epidemic is so overwhelming and it requires an overwhelming response,” Dr. Tom Frieden, the director of the Centers for Disease Control and Prevention (CDC), told reporters Tuesday after returning to the U.S. Monday from a trip to the affected countries.

Despite the efforts of health workers from the affected countries and elsewhere, cases of Ebola will continue to increase, Frieden said. Moments after his remarks, an aid group announced that another American doctor fighting the outbreak in Liberia has been infected.

Groups like Doctors Without Borders that are treating patients are overwhelmed by the high number of cases, and have had to turn away infected people because of lack of space. Frieden said he saw patients lying on the ground in some West Africa clinics. He stressed that Ebola is a global problem, and that closing off affected countries like Guinea, Liberia and Sierra Leone — many airlines have stopped flying there — will only worsen the outbreak by cutting off access to needed supplies.

“Getting supplies and people in is a big challenge,” Frieden said. “The more the world isolates and stops contact with these countries, the harder it will be to stop the outbreak.”

Contact us at editors@time.com.

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