A widening outbreak of deadly Ebola fever is threatening to overshadow next week's summit between African leaders and President Obama.
The three-day conference will bring nearly 50 African officials to Washington, D.C., for an unprecedented gathering that officials said could be a turning point in U.S.-Africa relations.
At least two African leaders will forgo the conference as a result, with the death toll topping 700.
And while the event's agenda has not changed, President Obama said Friday that some international guests will undergo additional screenings next week to ensure safety.
"We are taking the appropriate precautions," Obama said at a press conference.
"Folks who are from these countries that have even a marginal risk, or an infinitesimal risk of having been exposed in some fashion, we're making sure we're doing screening."
An administration official described additional steps to ensure the disease does not travel to the United States.
First, the government worked with international partners to ensure that no one who may be ill or exposed to the virus will attend the summit.
In addition to screening at ports of entry, health officials will be available to provide medical care to all attendees, and the White House will learn when anyone seeks outside treatment.
Members of the Secret Service and the Diplomatic Security Service are also receiving special briefings on Ebola.
The preparations highlight fears that a sick guest could cross the Atlantic, though officials said the likelihood is very small.
Centers for Disease Control (CDC) Director Tom Frieden downplayed the risk, noting that Ebola is a "dreadful disease" but does not spread through casual contact.
"You will not get Ebola from someone who is not showing obvious symptoms," Frieden told The Hill.
"There is no carrier stage as there is with other diseases. Someone is usually desperately ill and bleeding or has already died if they spread it."
Ebola emerged in Africa in the 1970s and wrecks the body by causing extensive bleeding. Nearly every victim dies from the virus, as there is no vaccine and no cure.
The United States is leading the response against the current outbreaks alongside the World Health Organization (WHO).
While U.S. officials have been upbeat about the possibility of containing the disease, WHO Director General Margaret Chan warned Friday that the rash of cases is getting worse.
"This outbreak is moving faster than our efforts to control it," Chan said in remarks at a meeting in Conakry, the capital of Guinea.
"If the situation continues to deteriorate, the consequences can be catastrophic in terms of lost lives ... and a high risk of spread to other countries."
"It has demonstrated its ability to spread via air travel," she added.
Frieden said the best way to protect Americans is to prevent the virus from spreading further in West Africa.
The agency is "surging" its resources on the ground, including sending 50 epidemiologists and other personnel over the next month.
"It's a big undertaking," Frieden said. "It's a big deal to do that safely and securely."
Ebola will not stay off American soil permanently. Two Americans infected with the virus will arrive for treatment in Atlanta in the next week.
Health officials are also working to educate the Transportation Security Administration and border control workers about how to spot symptoms.
Anyone traveling from affected countries to the United States this weekend will receive an initial Ebola screening prior to departure, U.S. officials said.
After that, anyone showing symptoms could be quarantined at U.S. or other airports.