Sheldon H. Jacobson is a computer science professor in the College of Engineering, University of Illinois at Urbana‐Champaign. He has conducted research on aviation security for more than 20 years.

The heightened security at airports after 9/11 could serve as a model for preventing the import of the Ebola virus. (Photo by Tom Pennington/Getty Images)

Ebola, once an abstract disease on a far-off continent, has now reached the United States. The recent disclosure that Thomas Eric Duncan flew in from Liberia while infected with the deadly virus has sparked calls for airports and airlines to take drastic action to prevent Ebola from entering the country again. Similar calls are being made around the world: In France, some airline crew members want flights to affected African nations to be grounded. In India, news reports say there has been discussion of giving some travelers blood tests. And in certain airports in west Africa, passengers are asked detailed questions about their health and submitted to temperature readings.

There is precedence for some drastic security measures in U.S. airports. Following the 9/11 terrorist attacks, for instance, the Federal Aviation Administration grounded all flights to prevent more air security breaches. At that time, this call was necessary and justified for a limited period because of uncertainty surrounding the day’s events. But halting flights to and from affected countries in western Africa would be a draconian measure, given the economic and health effects of such a move. The affected countries are already relatively poor and have limited resources for health care; isolating them would have tremendous humanitarian consequences.

Security measures implemented after 9/11 taught us a lot about what not to do. We learned that finding the one person who intends to do harm out of several million passengers is akin to finding a needle in a haystack. The Transportation Security Administration abandoned such an untenable objective many years ago when it terminated the Computer Assisted Passenger Prescreening System II, or CAPS II, due to overwhelming privacy concerns and the potential to ground many innocent travelers. U.S. airports have used risk-based security since then, but instead of looking for that needle, the TSA now identifies passengers who pose no risk to the air system – about 60 percent to 70 percent of travelers. The remaining passengers, for whom there is not enough information to rule out their threat, are subject to increased screening. That strategy focuses the right security resources on the right people. The result is a more secure air system at a lower cost, with less inconvenience to the majority of travelers.

Can the same concept be applied to screening for Ebola? The simple answer is yes. Screening passengers before they get onto an airplane is the best weapon available for limiting the spread of Ebola. Some African countries are already doing this, and the United States can augment that security once international travelers land or switch planes. The least intrusive approach would be to question passengers on their travel histories over the previous three weeks. Those with verifiable documentation indicating that they have not been exposed to Ebola during recent trips, such as hotel receipts from unaffected areas, should be permitted to continue their travels.

Those who cannot provide such detailed information or whose answers suggest an elevated Ebola risk should be subject to more severe restrictions, beginning with blood tests and, in extreme cases, required quarantine for up to three weeks. This may seem severe, but such consequences would also serve as an incentive for future travelers to document and create a paper trail for themselves to avoid unnecessary delays in entering the United States. Given the severity of the Ebola situation, the onus of proof must reside with the traveler to provide the necessary documentation to establish their level of exposure. Once in place, these measures should subject fewer than 10 percent of travelers to greater scrutiny.

Certainly, there are challenges to this approach, including determining what level of Ebola exposure requires quarantine. Targeting anyone who has been in a country affected by Ebola would be unnecessarily strict, since Ebola is only transferred by direct contact with an infected person’s bodily fluids. Quarantining travelers who have had interactions with people who have or may have the disease will be difficult. It relies on people to be honest about their level of Ebola exposure, and exposed people may be motivated to cover up their travel history to gain access to the American health systems, even if it exposes others to risk. Requiring verifiable documentation would help cut down on this problem.

Ultimately, it’s unlikely that the first case of Ebola in the United States will be the last case, whatever actions we take. Still, preventing the import of the virus into the country is an important goal in containing Ebola. Certainly, implementing the various levels of screening for Ebola will require a delicate balance between public health and personal freedom — similar to the debates that occurred when aviation security was augmented following the 9/11 terrorist attacks. But the severity of the Ebola threat requires vigilance. The challenge of Ebola prevention occurs at the interface of critical issues that include protecting the public, personal privacy, appropriate screening for a threat, and unpredictable human behavior. The ensuing days and weeks will be ripe for thoughtful and necessary discussion on these aspects of Ebola prevention.

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