A man who recently worked to help those infected with the Ebola virus in eastern Congo exhibited flu-like symptoms on Sunday and potentially could have exposed the ambulance crew and others, The Denver Post reported.

The initial tests came back negative, but the man and the crew were placed in isolation at the Infectious Disease Department of Medicine at Denver Health. The hospital—which is one of ten in the country designated to handle an outbreak– is reportedly “on normal operations” and there “is no threat or concern for patient, staff or visitor safety.”

The federal Centers for Disease Control are assisting and assessing the risks, the report said. The hospital’s lab tests have come back negative but a final determination will be made by the state health department, KDVR.com reported.

There is no specific treatment for Ebola, which is spread via contact with the bodily fluids of those infected, including the dead. Symptoms include fever, vomiting, diarrhea, muscle pain and at times internal and external bleeding. The virus can be fatal in up to 90 percent of cases, depending on the strain.

There were 54 Ebola cases, including 33 deaths, in the outbreak that was declared in early May in northwest Equateur province, Congo’s health ministry said. The outbreak is considered over.