UNITED NATIONS — Secretary-General Ban Ki-moon said Monday the international community urgently needs better early warning and rapid response to the next outbreak of disease — "a test that is sure to come."

The U.N. chief, who just visited Ebola-hit countries in West Africa, said the world must learn the lessons from the deadly outbreak, which go beyond strengthening public health systems.

Ban said he intends to explore with the 193 U.N. member states "what we can do to stay ahead of the next outbreak of disease."

The World Health Organization identified the first Ebola case in Guinea on March 21; on March 30 the virus crossed the border into Liberia; Sierra Leone reported its first two cases on May 30.

On June 20, with some 330 recorded deaths, Doctors Without Borders warned that the outbreak was "totally out of control." WHO didn't declare Ebola a health emergency until Aug. 8.

The epidemic in West Africa has become the largest in the world with some 18,500 people infected, mainly in Liberia, Sierra Leone and Guinea. Of those, more than 6,800 have died.

The secretary-general returned Sunday from visiting the three hardest-hit countries as well as Mali and Ghana, where the U.N. mission helping to eradicate Ebola is headquartered.

"My presence in the office today is meant to send an important message: where people show no symptoms, others should show no fear," Ban said.

He said the rate of transmission is coming down, but not fast enough.

"Ebola remains an emergency and there can be no let-up in our efforts," he said.