The head of the top U.S. public health institute said Sunday he is confident the United States will not see an outbreak of the fast-moving Ebola virus.
Speaking to NBC 's Meet the Press program on Sunday, Dr. Tom Frieden of the Centers for Disease Control and Prevention noted that infection control in U.S. hospitals and public health interventions will prevent the disease from spreading widely.
Frieden believes the response in West Africa is "getting more and more effective" in containing the virus that has killed nearly 3,500 people since the outbreak began late last year.
His comments come as the condition of the first known Ebola patient in the United States worsened. Thomas Eric Duncan, who arrived in the United States from Liberia two weeks ago, is now in critical condition in a Texas hospital.
A university study published in September in the journal PLoS Current Outbreaks estimates that Ebola is most likely to spread to nearby Ghana and Gambia next.
The study analyzes airline passenger traffic from the Ebola-stricken countries of Guinea, Liberia and Sierra Leone.
Outside of Africa, Britain, Belgium, France and the United States are at the most risk, according to the report that was published before the first U.S. case was identified.
By Oct. 3, the World Health Organization had documented cases in only two other countries: Nigeria, with 19, and Senegal with one.