The status of a patient with Ebola who was recently admitted to a specialized federal facility in Bethesda, Md., has changed from serious to critical condition. The American health care worker, whose identity hasn't been publicly released, was taken to the Clinical Center at the National Institutes of Health last week.

The patient being cared for in Bethesda contracted Ebola while volunteering in Sierra Leone, where the aid worker had been with the group Partners in Health. The person was flown back to the U.S. Thursday, aboard a private jet.

"No additional details about the patient are being shared at this time," the NIH says, adding that it has "no pending admissions of additional individuals with Ebola virus disease or exposed to the Ebola virus."

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