With a confirmed case of Ebola in Texas everyone is buzzing about Ebola's potential spread in the United States. Due to differing social practices and a vastly superior healthcare system the chances of a major epidemic in the United States are negligible. The effective transmission rate of other vector borne diseases in the United States compared to Central Africa is an order of magnitude lower. Excluding malaria which is endemic to Africa and inflates this number even more, for every 40 hours of life lost by the average American to similar diseases the average African loses a year of life. It is reasonable to assume that Ebola transmission and treatment would be similar.
However, Ebola is here and it is possible that more people will be infected. What are the chances that 100 or more people contract Ebola? The reproductive number of a disease is the average number of additional cases caused by each infection. For perspective, pertussis' number is typically around 15 and smallpox's reproductive number was around 6. The current outbreak in Africa has an estimated reproductive number close to 1.7; over the epidemic threshold. Based on awareness of the disease and the lower transmission rate of similar diseases, assuming a reproductive number under 1 in the United States is reasonable. Reproductive numbers less than 1 have a well-studied model know as the Borel distribution. If the reproductive number is .5 then the chance of over 100 total cases is around 1 in 42 billion; the chances of winning the Powerball jackpot are a mere 1 in 175 million. As the reproductive number approaches 1, the rate in Sierra Leone, the chances of over 100 people contracting Ebola approaches 7.96%. That may sound alarming but the United States isn't Sierra Leone. Instead of worrying about Ebola follow some simple advice to live a longer life, get a flu shot.
--S. Bradley Cole is a mathematician at Pivit, the gaming app that uses advanced algorithms to predict outcomes and percentages in real-time.
(Editor's Note: Want to know more about how things go viral? Here's a less frightening scenario.)
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