All communicable diseases have a number assigned to them that tell scientists and doctors how fast a disease is spreading. This number is always based on past outbreaks to start with and then, as the outbreak continues numbers are produced for the current outbreak. These will be revised as an epidemic continues.
Depending on whom you are talking to this number is referred to as the infection rate or the reproduction rate, they are the same thing and can be interchanged in a medical context.
The number to remember is 2.
The number 2 represents exponential spread in the medical world. A two or higher is very bad news. the higher the reproduction number the harder it is to control an epidemic.
Assigning the number 2 to a disease means that every one person who has the condition passes it to two others. Those two will then infect four people between them, those four will infect eight and so on. this is what doctors mean by exponential spread.
As the reproduction rate heads up towards 2 then the doubling time of known cases reduces, this is what has been seen in the Ebola outbreak in West Africa.
Based on the latest figures from the World Health organization, if the outbreak continues at it’s current pace then the reproduction rate for Sierra Leone could be as high as 2.26, 2.01 for Guinea and 2.02 for Liberia. (source)
As a comparison: The basic reproduction rate for the 1918-1920 Spanish flu pandemic, that killed 50 million people worldwide, was between 1.5 and 5.4 depending on which region of the world the data was taken from. (source)
This variation in BRR (Basic reproduction rate) is simple to explain. Sparse areas of population and areas where people are geographically distant from one another would have a BRR far lower than highly populated areas.
The Ebola victims that have been repatriated to their home countries for treatment are called controlled cases. Uncontrolled cases are the ones that are most likely to cause an outbreak in areas that have not been touched by the disease before. These are the cases that arrive from holidays, come to visit relatives, come into the country on business bringing the virus with them.
The patient currently in isolation in Texas flew in from Liberia whose current BRR is 1.83. He or she sought treatment six days after arriving in the country. Although Ebola is not infectious during the incubation period as soon as any symptoms show up that changes. Ebola mimics many diseases and often the person suffering from it will have no more than a sore throat for a few days, they may feel a little achy, just generally under the weather. Only after this do the more major symptoms start. The tell tale bleeding, both internally and externally is actually the last stage of the disease and its usually the point of no return for sufferers.
The problem with this is that no country on the planet has the facilities to check out every person who reports suffering from a sore throat and general malaise. People are going to slip through the net and it’s at this point that an epidemic of Ebola is most likely to occur.
With the winter flu season rapidly approaching the medical profession will be hard pressed to stop this if it escapes into the community.
Dr Thomas Frieden of the CDC said at a press conference:
“It is certainly possible someone who had contact with this individual could develop Ebola in the coming weeks,” Frieden told a news conference. “I have no doubt we will stop this in its tracks in the United States.”
I agree with the first half of his statement, and I hope to God he’s right about the second part.
There are some excellent articles on the sites listed below and for your convenience I have listed other useful articles here at Underground Medic.
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Contributed by Lizzie Bennett of Underground Medic.
Lizzie Bennett retired from her job as a senior operating department practitioner in the UK earlier this year. Her field was trauma and accident and emergency and she has served on major catastrophe teams around the UK. Lizzie publishes Underground Medic on the topic of preparedness.