New study suggests 21-day Ebola quarantine is off-base, virus could incubate longer

Hospital workers and public health officials in the U.S. have come under fire for a series of missteps in their response to the Ebola crisis, from initially misdiagnosing Thomas Eric Duncan to allowing a nurse who cared for him at a Dallas hospital to fly on a commercial airliner shortly before she too was diagnosed with the deadly illness.

Now an engineering professor with expertise in assessing the risks posed by pathogens claims he's identified another big problem with authorities' response to the crisis.

In a paper published Oct. 14 in the journal , Drexel University's Dr. Charles N. Haas argues that there's not enough evidence to support the recommended 21-day quarantine period for people suspected of harboring the virus.

"Twenty-one days has been regarded as the appropriate quarantine period for holding individuals potentially exposed to the Ebola virus to reduce the risk of contagion, but there does not appear to be a systemic discussion for the basis of this period," Hass said in a written statement.

Hass argues in the paper that outbreaks of Ebola in Zaire (1976) and Uganda (2000), as well as data from the first nine months of the current outbreak, suggest that there could be up to a 12-percent chance that someone could begin showing symptoms of Ebola after 21 days, according to the statement.

As Haas put it in an email to The Huffington Post, "the risk is certainly not zero of anyone beyond 21 days converting to symptomatic."

And as reported by the , a paper published recently in the indicates that Ebola incubation times can be longer than that. According to the paper, "approximately 95%" of patients studied began to show symptoms within 21 days of exposure.

If 21 days is too short, what's the right length for an Ebola quarantine? Haas doesn't say.

"This is really a policy decision that needs to be made balancing the various costs, and other considerations such as personal liberty, that are involved," he told HuffPost Science. "There needs to be a formal deliberative process involving quantitative modelers along with economists and those familiar with regulatory and legal considerations."

An email seeking comment from the federal Centers for Disease Control and Prevention went unanswered. Check back for updates.