A greater number of people exposed to the Ebola virus than the four publicly identified patients have been evacuated to the United States.

Dent Thompson, vice president of Phoenix Air Group, a private company contracted by the State Department to transport the patients back to the U.S. says many more people who had an 'exposure event' have been flown from West Africa by his company.

Dr Kent Brantly, a medical missionary to Liberia, was the first Ebola patient returned to the U.S. for treatment, followed by Nancy Writebol, also a missionary, Dr Rick Sacra who is currently being treated in Nebraska and a fourth, as yet unidentified doctor.

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Isolation chamber: Patients exposed to Ebola are placed in an isolation chamber for the 12-14 hour flights back to the United States from Liberia

Safety first: The tent-like space where Ebola patients are kept while being transported back to the U.S.

However, THompson says the number of patients is actually much higher.

'We moved a lot of other people who had an exposure event,' Thompson told Yahoo News.

'Many times these people are just fine, they just had an exposure. But you have to treat it as though the disease is present.'

The actual number is unknown, as Thompson says medical privacy laws and Phoenix Air Group's contract with the State Department prevent him from speaking about it in detail.

He did tell Yahoo News that his company has flown 10 Ebola-related misisons to West Africa in the past six weeks.

'Not everything we do is

a sick person,' he told Yahoo News, adding that Phoenix has transported supplies. 'We do basically whatever needs to be done.'

Evacuees: Dr Kent Brantly (left) was the first Ebola patient transported back to the U.S.; Dr Rick Sacra has recently been admitted to a Nebraska hospital after being flown from Liberia by Phoenix Air Group

Survived: Missionary Nancy Writebol credits God with her recovery, but is likely also grateful for the services of Phoenix Air, which flew her back to the U.S. in a plane described as an 'intensive care unit with wings'

The World Health Organization (WHO) said Tuesday that the death toll from the worst Ebola outbreak in history stands at 2,296 and is already likely to be higher than that.

President Barack Obama is pledging more U.S. assistance to help contain the Ebola outbreak in West Africa.

The White House says the president made the pledge in a telephone conversation Monday with U.N. Secretary-General Ban Ki-moon.

Obama has said previously that the deadly outbreak is a U.S. national security priority and that the American military will help set up isolation units and equipment in West Africa and provide security for public health workers.

The Bill and Melinda Gates Foundation has also pledged $50 million, on top of $10 million it has already committed, to support the emergency response to the outbreak in West Africa.

'It became clear to us over the last 7 to 10 days that the pace and scope of the epidemic was increasing significantly,' Chris Elias, president of global development for the world's largest charitable foundation, told Associated Press.

Thompson said he expects his company to continue flying patients back into the U.S. for the foreseeable future as aidf agencies attempt to quell the rising epidemic.