Dr. Kent Brantly, Nancy Writebol and Dr. Rick Sacra all contracted the disease while working in Liberia -- and all survived.
Spanish nurse's aide Teresa Romero Ramos got the virus while tending to stricken patients. She too lived.
But like the patients above, Thomas Eric Duncan and Spanish priest Miguel Pajares also received treatment in the West. Yet, they died.
While there might not be a single, conclusive answer, a series of factors may contribute to survival.
Early, high-quality treatment
This may be the most critical factor in beating Ebola.
The survivors in the United States all have one thing in common -- they were rushed to two of the country's four hospitals that have been preparing for years to treat a highly infectious disease like Ebola.
Brantly and Writebol were successfully treated at Emory University Hospital in Atlanta; Sacra was released from The Nebraska Medical Center in Omaha.
Duncan didn't go to one of those four hospitals. He went Texas Health Presbyterian Hospital Dallas with a fever and told them he'd recently returned from Liberia. Yet, the hospital initially sent him home with antibiotics.
Then, after he returned to the hospital much more ill, two nurses caught the virus. They have since been moved to more specialized facilities like Emory and the National Institutes of Health in Maryland.
But that doesn't mean someone who goes to a different hospital is doomed, CNN Chief Medical Correspondent Dr. Sanjay Gupta said.
"Keep in mind that this is still a very deadly disease," Gupta said. "In West Africa, the mortality rates are above 60%. I think it is better in the United States. But they're not going to be zero, I think no matter where somebody is."
After finding a hospital capable of treating Ebola, those who survive are usually rehydrated quickly.
"The most important care of patients with Ebola is to manage their fluids and electrolytes, to make sure that they don't get dehydrated," said Dr. Tom Frieden, director of the Centers for Disease Control and Prevention. "And that requires some meticulous attention to detail and aggressive rehydration in many cases."
And if an infected patient getting proper care normally has a strong immune system, the chance of surviving goes up.
But what may seem basic in the United States can be difficult to come by in West Africa, where Ebola has already killed more than 4,500 people-- because access to health care is limited.
Three Ebola patients -- Dr. Rick Sacra, NBC cameraman Ashoka Mukpo and Texas nurse Nina Pham -- all received plasma donations from Brantly. And all three have survived.
The theory is that Brantly's plasma contains the antibodies necessary to fight the virus.
"It's very fortunate that the three patients I've been able to donate to, they and I share the same blood type," Brantly told CNN's Anderson Cooper.
"I'll keep doing it as much as it's needed, as much as I can."
There was some controversy about why Brantly didn't give plasma to Duncan. But the problem came down to blood type, Texas Health Presbyterian Hospital Dallas said.
Drugs that haven't gone through clinical trials can be risky. But with a mortality rate of 50% in the current Ebola outbreak, a World Health Organization panel said it is ethical to offer medications to fight the virus -- even if their effectiveness or adverse effects are unknown.
The experimental drugs at the center of this Ebola outbreak are ZMapp, favipiravir, brincidofovir and TKM-Ebola.
Brantly and Writebol both took ZMapp, and both survived. But Pajares also took ZMapp, and he died.
The director of Emory's Infectious Disease Unit cautioned against viewing ZMapp as a surefire cure.
"They are the very first individuals to have ever receive this agent," Dr. Bruce Ribner said. "There is no prior experience with it, and frankly, we do not know whether it helped them, whether it made no difference, or even, theoretically, if it delayed their recovery."
Spanish nurse's aide Teresa Romero Ramos took the anti-viral drug favipiravir and also received antibodies from a survivor in West Africa. She is now free of the virus
In addition to getting a blood transfusion, Sacra received an experimental drug called TKM-Ebola, which the FDA recently approved for wider use.
Duncan took a different untested drug, brincidofovir. But he didn't receive it until six days after he was admitted
to the Texas hospital. Had he taken it earlier, the outcome might have been different.