In the wake of the news that a patient in Dallas has been diagnosed with the Ebola virus, there have been calls for US airports to screen arriving international passengers for the disease before allowing them to enter the country. On September 30, Republican Senator Rob Portman tweeted that the CDC should act to implement screening at the border "immediately."
Today’s CDC announcement shows the need for active screening for Ebola at U.S. points of entry. The CDC should act to implement immediately.— Rob Portman (@senrobportman) September 30, 2014
On October 6, President Obama announced that the US is "working on protocols to do additional passenger screening" for Ebola, both in source countries, and for travelers arriving in the US.
However, the reality is that increased screening of travelers isn't going to keep Ebola out. The disease can only be detected in someone who already has symptoms — and people flying to the US from affected countries are already screened for symptoms before they depart. That means that "additional passenger screening" would not have prevented the Dallas patient from entering the US, because he did not have any detectable symptoms, and may not even have been aware that he'd been exposed to the disease.
These calls for screening are ultimately driven by a belief that the disease can be isolated in Africa, but that's impossible. Viruses don't respect international borders. The only way to keep Ebola out of the US is to end the outbreak in West Africa. When the people of Liberia, Guinea, and Sierra Leone are safe from Ebola, Americans will be too. Additional passenger screening at the US border may be comforting security theater, but it's not going to make us safer.
There's no way to screen for Ebola before symptoms develop
Ebola has a long incubation period between the time when a patient becomes infected and the time that person starts to show symptoms. During the incubation period, which can last up to 21 days, the virus isn't detectable: there are no symptoms and there isn't enough of the virus in the bloodstream to show up on a test.
That means that there just isn't a way for border screening to detect all cases of Ebola, because some people may enter the country while still incubating the disease. For instance, Thomas Eric Duncan, the patient in Dallas, traveled to the US while still incubating the virus. He had no symptoms and didn't realize he was sick — and there was no way for any screening process to have figured out that.
The good news, though, is that patients aren't contagious before they have symptoms. So even though Duncan's illness wasn't detected before he reached the US, it appears that there is no danger he could have infected other passengers on his flights.
Patients are already being screened for symptoms before they reach the US
But what about patients who do have symptoms and are contagious?
Travelers are already getting screened when they depart from the three major Ebola-affected countries: Guinea, Liberia, and Sierra Leone. Airport staff take their temperatures and ask them whether they are feeling ill and if they have had any contact with people who could be infected with Ebola. If they do have a fever or other symptoms, they aren't supposed to board their flights until they have been tested to make sure they're not infected. On an October 2 press call, CDC Director Tom Frieden confirmed that a number of travelers have been prevented from boarding their flights because they had fevers or were otherwise judged to be Ebola risks.
That system isn't perfect, of course. Passengers might not admit to symptoms or to their history of contact with Ebola patients. They might not even know if they've had contact with Ebola patients. Duncan's case is instructive about that issue: he went through exit screening in Liberia but he apparently didn't indicate on the screening form that he may have been exposed to Ebola. It's not clear whether Duncan knew he had been exposed — the AP reports that he might have contracted the disease when he helped carry his sick neighbor to a taxi, but apparently Duncan and the woman's family believed that her abdominal pain was due to pregnancy complications, not Ebola.
However, testing on arrival in the US would have the same weaknesses as testing before departure. Duncan still had no fever when he arrived in the US. There is no reason to believe that he would have responded differently on landing to the same questions he was asked before departing. US airport testing wouldn't have prevented him from entering the country.
Border officials already have the authority to quarantine patients who they suspect may have Ebola
If an individual does arrive in the US with symptoms, border officials already have the authority to detain and quarantine that person until infection is ruled out.
That means that travelers who arrive in the United States with fever, vomiting, or other Ebola symptoms can be quarantined, even if there is no comprehensive airport testing regime in place. Frieden confirmed that there are quarantine stations at international airports throughout the US and that if an ill traveler arrives in the country after traveling to an Ebola-afflicted region, officials will intervene to isolate that person as needed.
The only way to completely stop Ebola from coming to the US is to end the outbreak in West Africa
The reality is that calls to institute airport testing, just like previous demands to stop flights to and from West Africa or to close our borders to people from one of the affected countries, are fundamentally demands that US authorities take some action to keep Ebola in Africa.
The idea that there is some simple solution that could keep this disease out is comforting: we want to believe that we can isolate the disease by isolating the countries that are struggling with it. But even if that idea is appealing, it's still wrong.
The only way to prevent Ebola from coming to the US is to end the outbreak overseas. "The bottom line here, the plain truth," Frieden said, "is that we can't make the risk [to the US] zero until the disease has been controlled in West Africa." As long as people are being infected there, there is a chance that someone will unwittingly carry the disease to the United States.
That means that isolating Liberia, Guinea, and Sierra Leone would be a bad way to keep the US safe because it would make it more difficult to send desperately-needed supplies and medical staff to the region. By protecting people overseas, though, we will also protect ourselves.