There are some particularly encouraging trends emerging in the WHO sitreps on the West Africa ebola outbreak, which suggest a break from the exponential curve and increase in the doubling time initially seen.
Using the data from the reports on the total number of cases and the percentage of cases in the past 21 days, we see this for the total number of cases:
Early on, we were near 50% for total cases - if we took 50% as the value (to keep the math easy), that would have indicated that cases had doubled over the last 21 days as of that report. As of the last sitrep, if that number was about 25% (math simplification op. cit.), which would indicate a doubling time about twice as long. At the value of 20% that we observe, this would ballpark a doubling time about 2,5 times as long.
Disaggregating the data by country is revealing, with what appears to be unambiguous slowing of transmission in Liberia:
Somewhat equivocal slowing in Sierra Leone:
And re-acceleration in Guinea:
These conclusions are all subject to the accuracy of the data collection, but it would seem that as more world attention and resources begin to be focused on stopping the current outbreak that initial signs of improvement can be seen. This should not lead to complacency but rather encourage the investment of additional resources.
WHO Situation reports: Ebola response roadmap