Health care workers have more than 100 times the risk of catching Ebola in Sierra Leone as the general public there does, according to a new report.

And it's not necessarily down to failed protective measures in hospitals. Health care workers form their own community, and when one gets sick or dies, he or she can infect fellow medics, the report finds.

The World Health Organization has been saying that health care workers such as doctors and nurses are at special risk of Ebola. It says 622 health-care workers have been infected and 346 of them have died in all the affected countries.

"They can ill afford to lose health care workers."

Sierra Leone already has far too few health care workers just about 2,400 for a country of 6 million people.

"They can ill afford to lose health care workers," said Dr. Peter Kilmarx of the U.S. Centers for Disease Control and Prevention, who led an investigation into the high infection rate in Sierra Leone.

Ten physicians have died of Ebola in the current epidemic, including Dr. Martin Salia, who died after being evacuated to the University of Nebraska for emergency treatment last month.

Salia wasn't even treating Ebola patients. He was a primary care doctor at a Methodist hospital, probably infected, experts believe, when he was treating a patient for other symptoms without suspecting he or she had the virus.

It's a story that CDC experts found over and over in their investigation of health care worker deaths.

"We think of health care worker infections as a failure of personal protective equipment," Kilmarx told NBC News. "But there are so many different ways that they are exposed there."

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High Risk: Health Care Workers Have 100x Ebola Rate