Another four U.S. Ebola aid workers flown back to U.S. for monitoring

CHICAGO (Reuters) - Another four U.S. healthcare workers were flown back to the United States for monitoring for possible exposure to the Ebola virus, U.S. Centers for Disease Control and Prevention said on Tuesday.

The return of the four U.S. healthcare workers brings to 16 the number of Americans who have returned to the United States from Sierra Leone since Friday, the CDC said.

That includes a healthcare worker in critical condition who is being treated for Ebola in a Maryland biocontainment unit run by the National Institutes of Health.

Most of the healthcare workers are employed by the aid group Partners in Health.

Only one of the 16 has tested positive for Ebola. The rest are being flown to Atlanta and Maryland, which have special biocontainment units. They are all undergoing monitoring for Ebola in self-imposed isolation as they wait out the remainder of the 21-day Ebola incubation period.

CDC spokesman Tom Skinner said the agency is still investigating the circumstances surrounding the exposures.