dr. kevin decock, an american, is country director for the centers for disease control in kenya.and members of his team have been in liberia and the other affected countries in recent weeks. jeffrey brown spoke to him this weekend in nairobi, kenya. >> brown: dr. kevin decock, thanks for talking with us am there is a report that a new estimate is in the works that may i have a worst case scenario-- scenario as high as half a million people am you can comment on that? >> yes. the doubling time of new cases of ebola virus disease in liberia is about every 20 days. so there is a total number of cases doubling about every three weeks. we're now up to 3, 4,000 cases, reported cases which may be a slight underestimate. so a very rapidly we do expect to see some tens of thousands of cases, and quite possibly by the end of the year, early next year, some hundreds of thousands unless this is-- unless this is slowed down. >> brown: this is exponential growth. so at this point this is out of control? >> at the moment, the increase in cases has been described as exponential, yes. and yes, cl