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Mailman School Ebola Expert Models the Likely Spread of the Disease

Wednesday, October 29, 2014
Author: 
— Interviewed by William McGuinness

Since the first case of Ebola was diagnosed in New York City on Oct. 23, there has been a daily barrage of news reports about the deadly disease. Public officials including Govs. Andrew Cuomo of New York and Chris Christie of New Jersey, as well as New York City Mayor Bill de Blasio, have weighed in on a range of issues, from mandatory quarantines to how the disease is transmitted.

At Columbia’s Mailman School of Public Health, researchers have developed a computer model that tracks and forecasts the growth of Ebola cases in West Africa, the epicenter of the disease. For Jeffrey Shaman, an associate professor of environmental health sciences who led the development of the model, that means that much of his day is devoted to sometimes arcane epidemiological measures such as the “basic reproduction number,” or R0, the projected number of cases generated by a single infected person in a fully susceptible population. If R0 is less than 1, the disease will extinguish itself. If it is greater than 1, it will spread—and the larger the number, the harder it will be to control. Right now the R0 in the U.S. is close to zero.

Shaman’s team is one in a league of researchers and public health experts from Mailman and Columbia University Medical Center that have provided local and global authorities with a scientific basis for their policies and response. Columbia Engineering has partnered with Mailman faculty and staff on a design challenge to find solutions to health workers’ most common field medicine problems. Epidemiologists including Dr. Ian Lipkin and Dr. Abdul El-Sayed have provided institutional expertise to the news media and general information to a concerned public. And, Shaman’s group provides regular status updates on the virus’ strength in West Africa—forecasts predicting cumulative infections and deaths six weeks into the future are generated each week and posted online.

Shaman spoke to Columbia News to answer some basic questions about the likely course of the disease.

Q In September, your team developed a model to forecast the spread of the Ebola epidemic. What can it tell us about the spread of the virus?

We’ve been updating our site and forecasts each week as new data becomes available. In Sierra Leone, where the number of new cases grew exponentially in August and September, we have been forecasting continued exponential growth. In Liberia, there is some evidence of slowed growth, but this may reflect under-reporting of case levels. Future growth of the outbreak will depend on intervention and control efforts. The health systems in West Africa have been completely overwhelmed, so continued, aggressive support is needed from the developed world.

Q What other factors affect the spread of a disease?

What’s made Ebola particularly hard to contain geographically is its incubation period—the time that you’re infected but in good health. It can be as long as three weeks before people become contagious. In each country you have a lot of mobility, so people can travel huge distances before any symptoms of illness appear. If the medical infrastructure isn’t built up and agile, which it isn’t, then there won’t always be the recognition needed to respond to the emergence of Ebola in a new location. In Liberia, the data indicate a slowing of the outbreak, but conditions on the ground call that data into question—it may still be growing but under-reported. As more resources like critical care hospitals, nurses and doctors arrive, hopefully this situation will improve.

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Q Concerns about the transmission of Ebola in the U.S. are considered overblown by most experts. How would you compare the basic reproductive number of Ebola in West Africa to that of the virus here?

If our infrastructure can respond appropriately—that is, isolate the infectious and those who have been in contact with the infectious, properly train and protect health care workers, and not let anyone slip through the cracks – then the basic reproduction number for Ebola in the U.S. should remain well below 1. However, this doesn’t mean there won’t be more imported cases. As long as the outbreak continues in West Africa, that risk will persist. In some sense, the West African Ebola outbreak is akin to a fire that has been allowed to spread and has grown much more difficult to extinguish.

Q How long until response workers can extinguish it completely?

In the middle of the summer we were thinking this was going to be a six-to-nine month problem. In September, that estimate was revised to 12-18 months.

Q You and your team also study the transmission of viruses in New York City. How does the spread of airborne upper respiratory viruses differ from the transmission of Ebola, which is spread through bodily fluids?

The short answer is we don't know. I would imagine that airborne viruses are more broadly dispersed, whereas something like Ebola is highly localized to infected persons and their immediate environment.

Q How have you and your colleagues at Mailman and the Medical Center worked together to battle misconceptions about the virus?

It’s all about communication—taking the time to provide information to the public and quell rumors and fears. There have been many rumors about Ebola, both in West Africa and here. One common concern is that the virus will become airborne, but this is an incredibly remote possibility. This message needs to be repeated continuously.