Health officials say two more American aid workers arrived in the United States on Wednesday night to be monitored for Ebola.
The two bring to 17 the number of Americans flown back from West Africa’s Sierra Leone since Friday for monitoring. None have tested positive.
All are connected to an unidentified American who returned to the U.S. last week after he came down with Ebola. He is in critical condition at a government hospital in Bethesda, Maryland.
The other aid workers are staying near hospitals with special isolation units in Bethesda, Atlanta, and Omaha, Nebraska, in case they get sick.
However, a Centers for Disease Control and Prevention (CDC) spokeswoman on Wednesday said two are now considered to be at low risk. They will go home for the 21-day monitoring period.
The virus is transmitted through direct contact with bodily fluids — saliva, sweat, blood, semen and other secretions — from a person who is experiencing symptoms. Those include high fever, diarrhea, vomiting, severe headaches, muscle pain, weakness, abdominal pain and unexplained bleeding, according to CDC.
The virus has killed nearly 9,000 people during its latest and deadliest outbreak largely centered in Guinea, Liberia and Sierra Leone.
Sierra Leone has accounted for two-thirds of the world’s cases recently. In the coming weeks, researchers plan to enroll 6,000 to 8,000 health workers there in an Ebola vaccine trial, supported by local researchers, the U.S. Centers for Disease Control and Prevention (CDC) and the Merck pharmaceutical company.