Corrections & Clarifications: An earlier version of this story incorrectly stated the number of new Ebola cases and the survival rate for those infected.
A second American health worker infected with Ebola was likely to arrive for treatment in Atlanta on Tuesday.
Health officials reported more deaths and cases worldwide, and more details surfaced on an experimental treatment.
Meanwhile, officials at Mt. Sinai Hospital in New York said they had admitted a man who had recently been to West Africa after he arrived at the emergency room early Monday with symptoms that are consistent with Ebola - high fever and gastrointestinal problems.
In a statement, Mt. Sinai said, "The patient has been placed in strict isolation and is undergoing medical screenings to determine the cause of his symptoms. All necessary steps are being taken to ensure the safety of all patients, visitors and staff."
The week ending Aug. 1 saw 163 new cases and 61 deaths, the health agency said.
The newest numbers mean the overall death rate stands at 55%. Some previous Ebola outbreaks have had death rates up to 90%, and medical experts have speculated that faster, improved medical care may play a role.
There is no approved medicine or vaccine specifically for Ebola, but supportive care, including maintaining fluids, can help.
Two Americans stricken with the virus in Liberia may be showing signs of improvement after receiving additional experimental treatments there.
Emory wouldn't comment on the condition of the patient in isolation, to protect the patient's privacy, says Vince Dollard, a hospital spokesperson.
Infection with the Ebola virus causes fever and headache in early stages but can lead to hemorrhaging, liver failure and kidney failure and death in rapid progression.
CNN said the experimental treatment given to Brantly and Writebol is an antibody drug called ZMapp and was developed by Mapp Biopharmaceutical.
That is one of several experimental therapies under development and previously untested in humans, says Thomas Geisbert, a professor at the University of Texas Medical Branch in Galveston. Geisbert says he plans to test ZMapp in combination with other therapies.
If the two patients are improving after the treatment, "that's fantastic," he says – but it may be difficult to determine whether the treatment made the difference. "There are a reasonable number of people who live even without treatment. … The longer you can keep someone alive, the more likely your immune system kicks in and fights this off."
Brantly is the first person to be treated for the illness in the USA. Most of the cases in the current outbreak have originated in Guinea, Liberia and Sierra Leone. Nigeria reported a second confirmed case Monday and three health workers who may be showing symptoms.
Meanwhile, Guinea President Alpha Cone and senior officials from Liberia and Sierra Leone broke away from the U.S.-African Leaders Summit in Washington, D.C., for private discussions about the Ebola outbreak with Health and Human Services Secretary Sylvia Mathews Burwell and CDC's Frieden, the State Department said.
"The group identified national and regional priorities and held intensive discussions on the types of assistance needed to mount an effective response," the State Department said.
Contributing: Donna Leinwand Leger