Computer Model Predicts 2 Dozen Ebola Cases in U.S. This Month

There could be as many as two dozen people in the U.S. infected with Ebola by the end of the month, according to researchers tracking the virus with a computer model.

The actual number will probably be far smaller and limited to a couple of airline passengers who enter the country already infected without showing symptoms, and the health workers who care for them, said Alessandro Vespignani, a Northeastern University professor who runs computer simulations of infectious disease outbreaks. The two newly infected nurses in Dallas don’t change the numbers because they were identified quickly and it’s unlikely they infected other people, he said.

The projections only run through October because it’s too difficult to model what will occur if the pace of the outbreak changes in West Africa, where more than 8,900 people have been infected and 4,400 have died, he said. If the outbreak isn’t contained, the numbers could rise significantly.

“If by the end of the year the growth rate hasn’t changed, then the game will be different,” Vespignani said. “It will increase for many other countries.”

The model analyzes disease activity, flight patterns and other factors that can contribute to its spread.

“We have a worst-case scenario, and you don’t even want to know,” Vespignani said. “We could have widespread epidemics in other countries, maybe the Far East. That would be like a bad science fiction movie.”

The worst case would occur if Ebola acquires pandemic status and is no longer contained in West Africa, he said. It would be a catastrophic event, one Vespignani says he is confident won’t happen.

“Let’s be rational for the next couple of months,” he said. “We aren’t going to have an invasion of cases. After November, we need to reassess the situation and see what is the progress of containment in West Africa.”

It’s reasonable to expect one or two more imported cases in the next couple of months, plus related infections in health care workers, he said.

It’s unlikely that Ebola will ever exceed 20 cases in the U.S. or Europe because of their extensive health care infrastructures, said Ramanan Laxminarayan, director of the Center for Disease Dynamics, Economics & Policy, a non-profit think tank in Washington, D.C. The problem in the developed world will center more on the economic impact, he said.

“The damage is not as much in the number of deaths as much as in the panic it creates and all the disruption it creates in trade and travel,” he said. “It’s important for public health officials to strike a balance between being serious and certainly not creating panic.”

“It’s not going to be like the movie ‘Contagion,'” he said.

The infection of two nurses who cared for Thomas Eric Duncan, the first person to be diagnosed with Ebola in the U.S., has some worried that the virus may be mutating and becoming more infectious. When trying to extrapolate those cases, people should remember five other Americans were flown to the U.S. for care, said Eli Perencevich, professor of epidemiology at the University of Iowa Carver College of Medicine. None of them transmitted the virus.

Average Americans shouldn’t see any risk from the virus outside of the medical community because patients aren’t terribly infectious until the disease peaks, Perencevich said. In industrialized areas like the U.S., those people will be in the hospital, he said. Health care workers, though, are uniquely vulnerable.

“There’s a high probability that there will be another person who comes in, no matter what we do, but the risk is in the hospital,” he said in a telephone interview. “As long as people who know they have been exposed to the virus get themselves quickly to the hospital, even after they have started a fever, it should be OK because they aren’t that infectious.”

Getting to the hospital could be difficult for some people, said Maria Cristina Garcia, a professor of history at Cornell University, who has written extensively about refugees and immigrants. While any international traveler could import Ebola, Garcia worries that the outbreak may give Americans another reason to fear or lash out against immigrants.

“An immigrant, like any other person in the U.S., is concerned about cost and confidentiality,” she said. “If he cannot afford a hospital stay, he might avoid seeking treatment until it’s too late. He might also fear coming forward for fear of stigma. Those of us who lived through the 1980s remember how Americans responded to the AIDS crisis during the early years.”

It’s possible that a handful of infected travelers could spread the virus to new areas, especially given its long latency period, said Jeffrey Shaman, who is modeling the outbreak at Columbia University’s Mailman School of Public Health. The models that show a possible range of cases in various countries are a good place to start, although there are so many variables that to some extent they are flying blind, Shaman said.

“Human folly and human nature plays into this,” he said in a telephone interview. “All these chains of human error can lead to these things emerging in little clusters. The real question is can we contain it.”

For that to happen, people have to limit close contact with anyone who might have an infection and quarantine those who have been exposed, said Wayne Getz, a professor at the University of California, Berkeley, who studies environmental science and is modeling how the Ebola outbreak can be contained.

The U.S. has the health-care infrastructure to prevent an epidemic, as long as the disease is detected early.

“It’s very important to rapidly detect and isolate cases,” Getz said. “If this isn’t done properly, we have a big problem in the United States. If it is done properly, we can control the spread.”

The real risk is that Ebola continues to gather steam in Africa and expands globally, said Irene Eckstrand, director of the NIH Models of Infectious Disease Agent Study. A consortium of about 100 scientists, based at the National Institutes of Health, mobilized in July to model the virus’ spread.

“At the moment Ebola is spreading exponentially,” Eckstrand said. “There’s no convincing evidence that it’s beginning to slow down. It can get out of hand very fast.”