One of the tenets for minimizing the risk of spreading the disease has been a 21-day quarantine period for individuals who might have been exposed to the virus.

But a new study by Charles Haas, a professor in Drexel University's College of Engineering, suggests that 21 days might not be enough to completely prevent spread of the virus.
Haas's study looked at previous outbreaks in Africa in 1976 (Zaire) and 2000 (Uganda) as well as the first 9 months of the current outbreak.
In both cases, data gathered by the World Health Organization (WHO) reported a 2-21 day incubation period for the virus - meaning that after 21 days if the individual hasn't presented symptoms they are likely not to be infected or contagious, researchers said.
"Twenty-one days has been regarded as the appropriate quarantine period for holding individuals potentially exposed to Ebola Virus to reduce risk of contagion, but there does not appear to be a systemic discussion of the basis for this period," said Haas.
Haas suggests that a broader look at risk factors and costs and benefits should be considered when setting this standard. With any scientific data of this nature there is a standard deviation in results.
In the case of Ebola's incubation period the range of results generated from the Zaire and Uganda data varied little, researchers said.
This might have contributed to the health organizations' certainty that a 21-day quarantine period was a safe course of action.
But looking more broadly at data from other Ebola outbreaks, in Congo in 1995 and recent reports from the outbreak in West Africa, the range of deviation is between 0.1 and 12 percent, according to Haas.
This means that there could be up to a 12 percent chance that someone could be infected even after the 21-day quarantine.

"While the 21-day quarantine value, currently used, may have arisen from reasonable interpretation of early outbreak data, this work suggests reconsideration is in order and that 21 days might not be sufficiently protective of public health," Haas said.
In its latest situation report on the disease, WHO reported 8,376 cases and 4,024 deaths from Ebola based on information provided by the Ministries of Health of Guinea, Liberia, and Sierra Leone.

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