In this article I want to address:
- The current status of air traffic from Ebola afflicted areas
- Mechanisms for spreading the disease
- Exactly where geographically Ebola has broken out
- The incubation period for Ebola
- The demographics of those dying from Ebola today
- The error of over confidence
It is very good news that Nigeria’s biggest airline Arik has suspended all flights to Liberia and Sierra Leone. We should remain hopeful that all airlines follow suit and suspend flights in and out of the afflicted areas. News reports concerning Ebola and their representation of difficulty in contracting the disease Global authorities on alert over Ebola outbreak from USA Today are likely false. Ebola has been shown to be spread through fluid droplets between monkeys and pigs and it is easily conceivable given a large enough density of afflicted people to be communicated the same way in humans. See From Pigs to Monkeys, Ebola Goes Airborne. For this reason it is clearly not a good idea to misrepresent the threat.
Yesterday I showed a chart of air traffic in the world but did not post an image of the afflicted regions. Below is an image posted by The Economist showing the areas afflicted by Ebola.
Yesterday in conversation I was asked what the demographics of those who die from Ebola are compared to those who die from wars. He also asked what the incubation period for Ebola was so as to understand the potential for spreading the disease without any knowledge of having it. His questions led me to reading research articles on Ebola and an understanding of the effect of research on our ability to protect ourselves from high risk situations. The best research I found was published by Centers of Disease Control and Prevention under the heading Emerging Infectious Diseases Volume 16, Number 7—July 2010 (*Note: This article has been pulled from the CDC website.)
The incubation period for Ebola, or the period between when you contract the disease and when you have symptoms, can be anywhere from 2 to 21 days with the medium period being 7 days. The incubation period reported is a data point with enough variance that we can accept it with extreme confidence. This makes the threat of accidental transport extremely high.
The information provided in the report about the demographics of those dying from Ebola are as follows:
Case-patients’ ages ranged from 3 weeks to 70 years (mean 34 years, median 35 years). Most 40 (36%) case-patients were crop farmers; 14 (12%) were healthcare workers.
Clearly, all members of society are at risk contracting the disease and it is not just the young or old that die from contracting Ebola.
The analysis of this report indicates that most contracted the disease because they participated in burial rituals and that the disease is, in general, hard to contract. It is on this point that we must be most careful. This is the point that USA Today is using to pacify our fears and misses the mark completely on the reality of how diseases and their interaction with the global auger of humanity spread. The spread of disease is much more like water poured on a table than water poured into a crafted channel. The water will spread according to least resistance and find invisible paths that our cursory observations of the table missed. Confidence and our desire to remain calm in this situation are our worst enemies. We do not have the luxury of believing that transmission is so difficult and our health care systems so robust that there is minimal threat.
Is it possible that somebody could be infected in one of these countries and fly to the U.S.? It is certainly possible. Given our health care system, it’s unlikely that we would have widespread disease as a result. We would be on top of it, and we would be able to contain it. Our health care system affords people access to gloves and gowns and personal protective equipment. I don’t think there’s reason for panic that we’re going to be hit with an outbreak of Ebola. – W. Ian Lipkin told National Geographic
Our analysis should be less concerned with what situation transmitted the disease and more with the percentage of contractions based on density without extreme mobility. The overall attack rate in some districts was 43 cases/100,000 population. What this number does not represent is the concept of acceleration and momentum that occurs in a population with enough density and rapid transportation escalating the probabilities of exponential growth. To exemplify this concept suppose Tom, a 35 year old business owner and long time allergy sufferer, contracts Ebola while on safari in Africa without having any idea that he has contracted the disease. Tom returns to New York city 3 days after being on safari and plays basketball at noon with a group of players he has played with for years. The players on the court change up from day to day and are known for entertaining business travelers in the finance industry from California, London, Tokyo, and Hong Kong. Within the first week of returning Tom plays basketball with 40 different men ranging in age from 20 to 55, half of whom travel back to their perspective cities clueless of their having been in contact with Ebola. How many people might have Ebola after three months if at the end of the first week 4 players, or 10%, have contacted Ebola from contact with Tom’s sweat while playing basketball? The number of possible people contracting Ebola after 3 months is 16 million people with a death rate of 40% amounting to approximately 6 million people. These numbers exaggerate the potential because they assume extreme body fluid contact at a rate of 40 people a week. It is not, however, unfathomable that the rate of close contact between the original 4 that contract Ebola is 1 person a week. The total number of people with Ebola under these circumstances is 1 million after 12 weeks.
Shutting down all air traffic in and out of the affected areas will greatly increase our ability to control the disease. More importantly, this situation is a situation to approach with caution, not over confidence. Our history is riddled with a reference to the past being our predictor of the future only to be surprised at the outcome. The past, even with respect to statistical analysis, is at best a potential predictor of outcomes. It is best not to place all our marbles in the basket of confidence.