Updated

Officials say an American health care worker who contracted Ebola while volunteering in Sierra Leone has improved to good condition at a federal hospital.

The National Institutes of Health said Tuesday that the patient had been upgraded from fair condition. He was in critical condition at one point.

He is being treated at the NIH hospital in Bethesda, Maryland, where he arrived March 13.

The patient's name and age have not been released. He was working with Partners in Health, a Boston-based nonprofit organization treating patients in Liberia and Sierra Leone since November.

Health officials have been monitoring about 40 other Americans who may have been in contact with the infected man. None had tested positive by late last week. A call to the Centers for Disease Control about their status wasn't immediately returned Tuesday.