Ebola has an incubation period of up to 21 days with many cases becoming symptomatic far earlier. Generally an infection will become apparent between days 8-10. Considering what we already know about the current case in the USA of Thomas Duncan and the history of the patient we can start to grasp when the next possible cases will appear in the event that transmission of the virus occurred.

Duncan first noticed symptoms on the 24th of September. He presented himself for treatment on the 26th at which point it can be assumed his symptoms were severe enough to motivate a trip to the emergency room. The patient was isolated on the 28th of September and reports indicate that various clean up activities of his apartment only concluded today. The following table will provide the possible second case dates:

Start Date 8-10 Range 21 Day Limit
24th September – Initial Symptoms 14/10/01-03 14/10/14
26th September – First Medical Trip 14/10/03-05 14/10/16
28th September – Isolation 14/10/05-07 14/10/18
3rd October – Final Clean-up 14/10/10-12 14/10/24

From the above table of possible date ranges and based on current information it can be concluded that any cases spreading from the first US case of Ebola will become symptomatic between the 1st of October 2014 and the 24th of October 2014. This only takes into account the potential for transmission prior to his isolation. There is a chance that transmission can occur during isolation as we have seen with health care workers in West Africa.

The most likely date range would begin today, the 3rd of October, and run until the 16th of October. Samples of close contacts will be sent for testing even if symptoms are not visible as a safety precaution. There is very little historical data confirming the exact point at which a test for Ebola would be positive in relation to the appearance of symptoms.