A recent study in PLoS Currents: Outbreaks suggests that the chance of getting at least one imported case of Ebola in the United States by late September could be as high as 18%.
The latest on the Ebola outbreak
According to data from the World Health Organization (WHO), there were 4,336 confirmed cases of Ebola and 2,218 confirmed deaths in West Africa as of Sept. 7. The international health agency says that controlling the outbreak could take as long as nine months, and the case total could reach 20,000 in that time.
However, U.S. experts say the WHO estimate is conservative. Researchers at several institutions say the case total could reach 20,000 in one month rather than nine.
Researchers at Virginia Tech say that scientists working on a National Institutes of Health-sponsored project called Midas, or Models of Infectious Disease Agent Study, estimate that the outbreak will last 12 to 18 months and that the case total will be very high.
"We hope we're wrong," Bryan Lewis, a Virginia Tech epidemiologist involved in the project, told the New York Times.
Could Ebola spread outside the African continent?
This month, a group of researchers published a report in PLOS Currents: Outbreaks that outlines the risk of Ebola spreading outside of Africa.
For the report, researchers analyzed the flow of airline passengers coming from West Africa to countries such as China, Egypt, France, Germany, India, Italy, Spain, South Africa, Saudi Arabia, and the United States.
Overall, they wrote, "[r]esults indicate that the short-term (three and six weeks) probability of international spread outside the African region is small, but not negligible."
Of the 13 countries analyzed, the United States was among the least likely to see an Ebola case. The researchers determined that there is a 1% to 18% chance that one case will enter the United States by Sept. 22.
But with time, the risk will increase, the researchers warn. "What is happening in West Africa is going to get here. We can't escape that at this point," says lead author Alessandro Vespignani.
However, the researchers do not anticipate a large outbreak in the United States. "What we could expect, if there is an importation, would be very small clusters of cases, between one and three," Vespignani says.
The researchers estimated that there was a more than 50% chance of Ebola spreading to Ghana by the end of the month. Gambia, Ivory Coast, Kenya, Morocco, and South Africa also have a high chance of seeing Ebola cases soon, according to the study. The risk of an Ebola case appearing in the United Kingdom by late September is about 25%, according to the report.
Reducing the number of air travelers from the area by 80% would delay the spread of Ebola by a few weeks, the researchers estimated.
Even if an Ebola case appears in the United States, health systems say the country is well-equipped to contain the outbreak. Still, U.S. health experts need to be vigilant.
"We certainly need to make sure that staff and leadership of American medical centers understand the implications of Ebola," says study co-author Ira Longini, explaining, "We need to have diagnostics in place to identify Ebola quickly. We need quite a few local labs to do this and not just rely on sending samples to the CDC. And we need to make sure isolation and quarantine of contacts takes place. If it doesn't, we could have a small cluster of cases" (McNamee, Medical News Today, 9/10; Knox, "Goats and Soda," NPR, 9/4; Belluz, Vox, 9/7; Grady, New York Times, 9/12).