As the Ebola outbreak in West Africa continues to spread, isolated cases will likely make their way to the United States, with new estimates showing there is a nearly 20 percent chance this will occur by the end of September, according to researchers from several institutions, including the University of Florida.
The analysis, published September 2 in the journal PLOS Currents: Outbreaks, combined patterns of international travel with estimates of how fast Ebola is spreading to calculate how quickly the disease might move to different locations.
Although some unexpected cases in the U.S. are likely inevitable, researchers anticipate they will be quickly isolated, not reaching any sort of outbreak level currently found in West Africa. Currently, the U.S. has imported three cases knowingly for treatment.
“We would assume that the U.S. would have sufficient capacity to test people and treat them. We would not expect any real transmission in the U.S.,” said Dr. Ira Longini, a professor of biostatistics in the UF colleges of Public Health and Health Professions and Medicine.
Initially, the disease is expected to spread to currently unaffected African countries, which further increases the likelihood of it spreading beyond the continent’s borders. There is not a high level of international travel among some of the affected countries, such as Liberia and Sierra Leone. But Nigeria, where the outbreak has also spread, is linked to many countries across the globe.
In fact, according to the study, as many as 6,000 passengers travel from Nigeria to the U.S. each week. In addition, many airline passengers go from Nigeria to other countries outside of Africa. Within the past week, Ebola also spread to Senegal, home to a major international hub in Dakar, its capital.
As the outbreak affects more metropolitan areas with international airports, the chances of unknowingly infected passengers bringing the virus with them to new locales is highly probable, said Dr. Longini, the co-director of the Center for Statistics and Quantitative Infectious Diseases at UF’s Emerging Pathogens Institute. Dr. Longini collaborated with senior author and physicist Dr. Alessandro Vespignani of Northeastern University, and other colleagues on the study.
Although it seems logical to assume that stopping international air travel would stem the spread of the outbreak, the researchers’ analysis showed it actually would have little effect. For example, reducing air travel by 80 percent would only prevent Ebola from spreading temporarily.
“Studies have shown the quarantining of entire villages and countries is highly ineffective, and this analysis shows that yet again,” Dr. Longini said. “Surveillance and containment, which includes the isolation of cases and quarantine of close contacts, is the only intervention strategy that works that is available.”