Projecting the path of Ebola is not a simple task. There is a lack of historical data to accurately model an outbreak as large as the current one in West Africa meaning all predictions and projections should be treated as speculative. The data used to model any prediction is based off official statistics and does not generally take into consideration under reporting or incorrect data.
The simplest of models use basic but unfortunately inaccurate mathematics to calculate the number of cases at a point in time by adding the growth rate daily. This is simple mathematics and a good way to get a quick idea of the potential number of cases but a virus does not always continue to spread in an exponential fashion. Several factors can change the growth rate including geography, intervention, weather and human behavior.
More accurate models will attempt to factor in the doubling rate of the virus and perhaps include basic limits around populations of an affected area. These models provide more realistic data to work with but still do not provide an accurate model.
The following projections forecast the Ebola outbreak and potential case count for October as follows:
20000 Variable Transmission
11000 Exponential Smoothing
15000 Exponential Cumulative
It is very likely that we will see more than 15000 cases by the end of October 2014 based on current reporting. The CDC report which predicted between 550000 and 1.4 million case by early next year factored in under reporting. Adjusting the 15000 by a factor of 2.5 to reach 37500 potential cases of Ebola within the next 30 days with as many as 26000 dead.
Predictions around the spread of Ebola in the USA are impossible at this stage. It is possible that the first case of Ebola in the USA will have a first wave of infections based on reports that the patient was infectious for as many as 4 days and further reports indicating that he was in contact with family members including children. It is likely that 3-12 cases could have been generated based on the current information available.