An American health care worker who contracted Ebola while volunteering in a Sierra Leone treatment unit has been downgraded to critical condition at the National Institutes of Health, doctors said Monday.  The agency said in a statement that the patient's status was changed from serious condition. He is being treated at the National Institutes of Health's hospital near Washington.  "We are intensively treating the patient," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at NIH.