Two to 21 days. If a person is exposed to the Ebola virus, that's the timeframe in which the symptoms of the disease can manifest. The disease kills about half of those it infects.
That's the reality for the friends of Thomas Eric Duncan, the first victim of Ebola to die in the United States, who made contact with him before his hospital admission. According to NPR, the family that made contact with Duncan "has been ordered not to leave their home and is banned from hosting any visitors until the 21-day incubation period for Ebola has passed." So does that mean that on the 22nd day, they are in the clear, completely safe from contracting Ebola?
No. Sadly, it's isn't so simple.
"There is no quarantine time that will provide absolute assurance of no residual risk from contagion," Charles N. Haas, a microbiology threat researcher at Drexel University, writes in a recently published paper in the Journal PLOS Current Outbreaks.
Symptoms typically begin to appear after nine days, but the World Health Organization has even recorded instances of a person contracting the disease after 30 days.
A few weeks ago, when Ebola was starting to permeate the news, Haas began to wonder how WHO came to its 21-day quarantine recommendation for Ebola. Haas then compiled all the available data on previous outbreaks. What he found was that, thankfully, there aren't many data on past outbreaks. In the past, Ebola has affected a few hundred people at a time; not the thousands who have been blighted in the current crisis. The small number of data points means that while health authorities may have a good idea of how long Ebola can remain dormant in the body, they do not know the upper limits of what is possible.