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A 21-Day Quarantine for Ebola May Not Be Enough, Study Says

Quarantine times are a murky science.

The recommended 21-day quarantine period for Ebola is likely based on data from just two previous outbreaks in Zaire and Uganda, and we don't even know that for sure, according to a new study published in PLOS: Outbreaks.

A new analysis of more Ebola outbreaks suggests that 21 days might not be long enough—there's a 12 percent chance a patient could still manifest symptoms later.

Quarantine periods are meant to last long enough for a patient to manifest symptoms of a virus. If they don't, they're likely not infected. According to Charles Haas of Drexel University, who authored the study, the exact scientific origins of the World Health Organization's recommended quarantine period for Ebola are murky.

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The recommendation could be traced to data from the 1976 Ebola outbreak in Zaire and the 2000 outbreak in Uganda, both of which reported incubation periods of 2-21 days, but nobody can be certain.

A more concrete approach is needed to determine an appropriate quarantine period, Haas wrote, so he analyzed data from the 1995 outbreak in the Congo and the current one in West Africa.

After examining the newly expanded data set, Haas discovered that the probability of excedence for Ebola incubation was .1 to 12 percent. "In other words," he wrote, "from 0.1 to 12 percent of the time, an individual case will have a greater incubation time than 21 days."

Data from the 1995 Congo outbreak suggests that a quarantine period of 31 days might be more appropriate.

Moreover, data from the 1995 Congo outbreak, which documented more than twice as many patients as the '76 Zaire study, suggests that a quarantine period of 31 days might be more appropriate.

According to Haas, the 21-day quarantine time was reasonably arrived at based on the data available, but lack of a systematic conversation has led to an inadequately robust estimate. The ongoing outbreak in West Africa, as morbid as it sounds, could provide an opportunity for scientists to come up with a better number; so far, it's produced more than four thousand cases with usable data.

"Outbreaks such as the current West Africa EBOV [Ebola Virus] are presenting an opportunity for careful collection of data sufficient to revise and update (perhaps in an adaptive fashion) such recommendations," Haas wrote.

The spread of Ebola in West Africa has been attributed to lapses in procedure: not enough doctors, resources, knowledge, and broken protocol. Fear mongering doesn't do anybody any good, and Haas' findings shouldn't be taken as an invitation to panic. Instead, they point to the need for rigorously followed procedures, and an equally rigorous vetting process for them.