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Seattle Scientists Predict Spread of Ebola Outbreak

October 30, 2014

As infectious disease epidemics and outbreaks grow more numerous and more complicated, specialized scientists continue to figure out ways to track, predict and prevent them. 

Harborview Medical CenterThe Ebola outbreak in West Africa is just one of a number of infectious diseases that erupt in outbreaks, epidemics and pandemics every year. As viral and bacterial infections have grown more numerous and the way they spread more complicated, scientists have had to has had to adapt and modify their methods of predicting, tracking and preventing them. As doctors at Harborview Medical Center prepare for the possible arrival of Ebola, a team of mathematicians and computer programmers use ever more complicated models to predict the spread of disease and advise policy makers on the ground. They are even beginning to predict where and when outbreaks might happen. But when they occur unexpectedly, like Pertussis or ‘Whooping Cough’ in the pacific northwest in 2012, epidemiologists must use different scientific means of bringing them under control. 

Nils Cowan: In Seattle, at the renowned Harborview Medical Center, Director of Infectious Disease Control, Dr. John Lynch, is preparing for one of the biggest events in the hospital’s history – an event he would rather not see happen.

Dr. John Lynch: Here at Harborview we see patients from all over the world and all over our community with pretty much any infectious disease you can name, ranging from tuberculosis to herpes zoster, shingles, chicken pox, meningitis. You name it, we’ve pretty much seen it – except for the one we’re talking about today.

Nils Cowan: Harborview has already modified its protocol based on current Ebola cases.

Dr. John Lynch, Director of Infectious Disease Control at Harborview Medical Center.

Dr. John Lynch: So this is the clean site.  This is the place where healthcare workers put on all their gear.  Full coverage of the body, boots, double gloves. If you look at nurses who are working with Ebola, they’re spending hours in the room.  And what we’re really recognizing is that masks like these aren’t quite comfortable enough to maintain that for that amount of time, so we’re moving towards gear more like this, this is a PAPR mask which goes over your head, and is attached with a hose back to this filtration unit which pumps air in and it makes it more comfortable, kind of free flowing air.  The room where the patient will be taken care of is considered a potentially infectious area and all precautions are taken when you go through that threshold.

A negative pressure room at Harborview Medical Center, potentially used to treat Ebola patients.

Nils Cowan: Inside, everything is focused on treating the patient while containing the spread.

Dr. John Lynch: This is a negative pressure room, which means all of the air is pulled from the outside in.  That way any airborne infectious diseases are contained in here.  Ebola virus is not one of those but we just take extra precautions for all those types of situations.  We also want to make the room very easy for cleaning, easy for getting around and not having anything extra that needs to be disposed of.  For instance some of these extra backup blood pressure cuffs, this, the normal garbage you see over here would also be removed and we really focus on the idea of a single waste stream.

Our engineering staff is building a prefabricated wall that would go right in this space which would provide an area for the healthcare worker to decontaminate their gear in a very specific way with bleach and our other protocols, and then when they leave the space they would be told how to remove all their gear in a very prescribed fashion by a site director.

Nils Cowan: While the staff at Harborview readies themselves for individual Ebola cases coming into the U.S., another specialized team only a few miles north at the Fred Hutchinson Center is tasked with tracking and predicting the spread of outbreaks throughout the globe. Led by Dr. Betz Halloran, Fred Hutch’s newly designated Models of Infectious Disease or MIDAS center tracks epidemics of all kinds, including Ebola.

Dr. Betz Halloran: We are interested in the dynamics of infectious disease, the spread in populations, and also in particular how interventions would work to slow down the spread.

Nils Cowan: And when the future of any outbreak is being debated, experts like Dr. Halloran and her team turn to mathematics.

Nearly every epidemic follows a similar bell curve pattern corresponding to a key number for epidemiologists, the reproductive rate, or how many people on average are given the disease by each infected individual.

At the beginning, or exponential phase, experts use various mathematical formulas to predict the potential spread in cases.

Dr. Betz Halloran: Once it starts spreading then we use an exponential growth function and then we can see how it will take off if there’s no intervention and there’s no saturation of disease.

Nils Cowan: Equations like this allow disease specialists to present a range of potential scenarios for the early phase of an outbreak. But to get the most accurate picture of how an epidemic might evolve, Halloran and her team take advantage of modern computing power to create what are called stochastic models, which can simulate entire worlds.

Dr. Betz Halloran: In those models, every individual appears in the model.  We actually can follow a person they go to work, they can live in a house, they can go to a funeral.  If they get sick they can go to a hospital. So we have hospitals.  We’re now working on modeling Liberia and so we have to have all of these different areas that people can go to and different behaviors that they follow.

Specialized Team at Fred Hutchinson Center

Nils Cowan: Using census data and demographics, travel patterns and statistics, and all of the known information about a particular disease, modelers can alter the simulation in millions of different ways.

Dennis Chao, Senior Staff Scientist, Fred Hutch: The model does exactly what you tell it to do, so if you know the disease really well, like Influenza we know how it transmits reasonably well, there’s a lot of experience, we can predict it pretty accurately, but for other diseases that we know less about, like say Ebola, there’s a lot of uncertainty.  Instead of saying well that model’s right and that model’s wrong, you run the model with a range of parameters saying we think that Ebola’s this transmissible, but it might be even more transmissible than that, we run the two scenarios, you can see the difference and say, well here’s the consequence of the uncertainty of what we know about the disease.

Nils Cowan: But these elaborate models don’t only predict the spread of diseases, their main interest for policy makers is to test different ways of stopping them.

Dr. Betz Halloran: You can see what happens when you do interventions like now they’re putting together these Ebola treatment units which are going to keep people out of the hospitals and so now we can also model Ebola treatment units and put those into the model and see what happens if people go to those instead of going to the hospitals, or in the case of flu of course, we have vaccines.  And then you have to make all the assumptions about how the vaccine works and exactly, you know, who would get vaccinated and so there’s a lot of options.

Nils Cowan: And with the increasing cost in both dollars and human suffering from infectious diseases worldwide, this field of expertise is growing quickly.

Dr. Betz Halloran: The amount of demand for modeling at the population level of interventions is almost unlimited right now, and I think it’s going to continue to grow and it’s our responsibility as good scientists to make sure we do the best job possible and to make our results accessible to the population as a whole.

Nils Cowan: Specialists like Halloran and Dr. Lynch are careful to look at Ebola in its historical context, as yet another epidemic that we have the knowledge and tools to defeat.

Dr. John Lynch: To be successful in my specialty it would actually result in having no infectious diseases anywhere.  We know that’s just not true. Infectious diseases are part of humanity, they’ve been with us forever.  And so recognizing that where one may be taken care of, a new one will arise.  And so we have to think about what’s in the past but we also have to think that this is going to continue on into the future.  As much as I want these diseases to go away, we’ll never extinguish them all.

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Nils Cowan

A native of Calgary, Canada who cut his teeth in the documentary industry of Washington, D.C., Nils moved to the Pacific Northwest in 2009 after working on a National Park Service film about Mt. Rainier and falling in love with the area. He has been producing non-fiction content for thirteen years, from broadcast and independent documentaries to museum films and non-profit PSAs. One of his most recent films, 'Beyond the Visible’ which reveals the inner workings and transformational science of the Very Large Array Telescope in New Mexico, was just awarded the 2014 Cine Golden Eagle Award for non-fiction storytelling.  Nils lives in Seattle with his wife and two kids.

More stories by Nils Cowan

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