American Who Contracted Ebola in Africa Now in Critical Condition

Twelve other health care workers are under observation, officials said.

An additional 12 individuals transported from West Africa are being monitored for the Ebola virus, officials said.

The current Ebola outbreak in West Africa is the deadliest in history. Though it has slowed down since its peak last year, there have been nearly 25,000 confirmed cases and more than 10,000 deaths, according to the latest numbers from the CDC.