Top medical experts studying the spread of Ebola say the public should expect more cases to emerge in the United States by year's end as infected people arrive here from West Africa, including American doctors and nurses returning from the hot zone and people fleeing from the deadly disease.
But how many cases? No one knows for sure how many infections will emerge in the US or anywhere else, but scientists have made educated guesses based on data models that weigh hundreds of variables, including daily new infections in West Africa, airline traffic worldwide and transmission possibilities.
This week, several top infectious disease experts ran simulations for The Associated Press that predicted as few as one or two additional infections by the end of 2014 to a worst-case scenario of 130.
"I don't think there's going to be a huge outbreak here, no," said Dr David Relman, a professor of infectious disease, microbiology and immunology at Stanford University's medical school. "However, as best we can tell right now, it is quite possible that every major city will see at least a handful of cases."
Relman is a founding member of the US Department of Health and Human Services advisory board for biosecurity and chairs the National Academy of Sciences forum on microbial threats.
Until now, projections published in top medical journals by the World Health Organization and the US Centers for Disease Control have focused on worst-case scenarios for West Africa, concluding that cases in the US will be episodic, but minimal.
But they have declined to specify actual numbers. The projections are complicated, but Ebola has been a fairly predictable virus, extremely infectious, contagious only through contact with body fluids, requiring no more than 21 days for symptoms to emerge.
Human behavior is far less predictable, people get on airplanes, shake hands, misdiagnose, even lie.
So far, eight Ebola patients have been treated in the US and one has died. Six became infected in West Africa: three doctors, a nurse, an NBC News cameraman and a Liberian man, Thomas Eric Duncan, the first to arrive undiagnosed and the first to die. He was cared for at a Dallas hospital, where two of his nurses were also infected but have recovered.
Dr Ashish Jha, a Harvard University professor and director of the Harvard Global Health Institute, said he's not worried about a handful of new cases in the US. His greatest worry is if the disease goes from West Africa to India. "If the infection starts spreading in Delhi or Mumbai, what are we going to do?"
Dr Peter Hotez, founding dean of the National School of Tropical Medicine at Baylor College of Medicine and director of the Texas Children's Hospital Center for Vaccine Development, pegs the range of cases in the US between five and 100.
The Centers for Disease Control and Prevention prefers not to focus on a particular number. But spokeswoman Barbara Reynolds said Ebola will not be a widespread threat as some outside the agency have warned.
"We're talking about clusters in some places but not outbreaks," she said.
