Are 21 days enough? Ebola quarantine period comes into question



With the first cases of Ebola Virus (EV) hitting the United States and the threat of a West African epidemic heightening to a global pandemic, every effort is going into assessing and reassessing strategic priorities to curtail the spread of this deadly virus.

The current quarantine period for individuals with suspected exposure to EV is 21 days, a number based on the maximum incubation time observed in previous outbreaks. However, a recent study by Charles Haas, PhD, from Drexel University suggests that this may not be sufficient to retard the dissemination of the virus.

His study, published in PLoS Currents: Outbreaks outlines earlier systematic studies on the incubation time of various pathological agents and their corresponding incubation time distributions. The data revealed that none of the distribution times had an upper limit. Therefore there is no quarantine time that can provide an absolute assurance of no risk from contagious transmission.

Obviously, an acceptable residual risk point needs to be set when deciding upon a suitable quarantine time and therefore considerations such as degree of transmissibility and degree of severity need to be assessed for a given contagion.

The current quarantine period for individuals with suspected Ebola Virus of 21 days comes from the World Health Organisation’s (WHO) assessment based on earlier disease outbreaks in Zaire and Uganda in 1976 and 2000, respectively, where the maximum observed incubation period was 21 days with little to no variation.

The quandary with regards to the correct quarantine period comes from data from other EB outbreaks in Congo, in 1995, and the current outbreak in West Africa where there is a deviation in incubation times of between 0.1 – 12 %. In real terms this means there exists up to a 12 % chance that someone can remain infectious after the proposed 21 day period.

Clearly then, a re-examination of a suitable quarantine time, based on all available data from previous outbreaks, may be needed to ensure maximum efforts are being made to minimize the spread of Ebola Virus.


The full Drexel report is available at image licensed for reuse from




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Joanne Euden

I am a postdoctoral research associate, funded by the British Heart Foundation (BHF) at Cardiff University where I work on the structure-function relationship of the cardiac Ryanodine Receptor. I completed my doctorate in 2007 in biophysics from the Univeristy of Southampton where I studied protein-lipid interactions of the mechanosensitive channel (TbMscL). I am currently considering my next career move.

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