The World Health Organization issued a dire Ebola warning on Monday concerning Liberia, saying that the number of afflicted patients was increasing exponentially, that nearly all the country has confirmed cases and that all new treatment facilities were overwhelmed, “pointing to a large but previously invisible caseload.”

The description of the crisis in Liberia, which along with Sierra Leone and Guinea are the three West African countries at the center of the worst Ebola outbreak ever recorded, suggested an even more chaotic situation in Liberia than had been thought, with the highest cumulative numbers of reported cases and deaths.

In another ominous piece of news, the organization said one of its own doctors working at a government-run Ebola treatment center in Freetown, the capital of Sierra Leone, would be evacuated after having tested positive for the disease.

Emory University Hospital in Atlanta, which recently treated and discharged two American missionary health workers infected with Ebola, said in a separate announcement that it would be receiving a third patient by air ambulance from West Africa on Tuesday. It was unclear if that patient was the same person, whose identity was not disclosed. At the same time, the authorities in Sierra Leone elaborated on their three-day plan, announced Saturday, for a nationwide curfew this month to allow emergency teams to visit every home in the country of six million from Sept. 19 to 21 to find people infected with Ebola and remove the dead.