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Airport Screening Would Not Have Stopped Ebola at the U.S. Border

Asymptomatic patients make the virus tough to detect

Mike Stone/Getty Images

The U.S. has its first case of Ebola and Senator Rob Portman, Republican from Ohio, thinks the officials at the Centers for Disease Control should take that as a signal to do more:

This wasn't just some random tweet. Portman made a similar call several weeks ago, via a letter he sent to CDC Director Thomas Frieden. As he noted at the time, border patrol agents at ports of entry already conduct “passive screening.” That means they look for obvious signs of Ebola when travelers report that they have been to affected areas of the world, like Liberia or Sierra Leone.

Travelers go through more aggressive screening when they leave West Africa, as Olga Khazan of the Atlantic explains. If you get on a plane from one of those countries, you'll have your temperature taken. If you have a fever, you'll get a blood test to see if you have Ebola antibodies. This is what most people interpret "active screening" to be, although Porter's office exlpained to me later that's not actually what he has in mind. (See note below.)

Problem is, this sort of active screening would almost certainly not have kept the Dallas patient from entering the U.S., for the very same reason it didn't prevent him from getting on a plane in the first place. According to the CDC, the infected traveler to the U.S. had no symptoms when he arrived in the U.S. on Saturday, September 20. A temperature test at a U.S. airport woudn’t have picked up anything—and that would have been true for at least another four days, because it wasn’t until Wednesday the 24th that he started to feel sick and run a fever. 

Public health experts I consulted quickly on Tuesday thought that was entirely predictable, given that Ebola has a long asymptomatic period of up to 21 days. Short of putting all travelers from affected areas into quarantine for three weeks, they said, airport screening isn’t likely to do much. “The idea is misguided,” said Howard Markel, a professor of medicine and communicable diseases at the University of Michigan and author of When Germs Travel. “It would not have worked in the case of an asymptomatic person. Airport screeners look for obvious signs, such as high fever and other visible or measurable signs of illness.”

Dan Kelly, an infectious disease specialist at the University of California-San Francisco, had a similar take. "Increased border control measures wouldn't have made a difference in this case and in cases like this one which were considered by CDC guidelines as a 'no known exposure,' " said Kelly, who for years has worked at a clinic in Sierra Leone. "There is still a small risk of developing symptoms during the incubation period, [but] self-monitoring and a clear emergency protocol for onset symptoms are adequate protection for returning health workers and those around them."

Screening might be more successful if it involved blood tests. But that would have enormous practical implications, for reasons Patrick Tucker explained in DefenseOne over the summer:

The presence of antibodies in the blood is a much more conclusive sign of the deadly virus. Unfortunately, subjecting hundreds or possibly thousands of passengers to a blood test for Ebola would be practically impossible in a major airport without slowing International air travel to a halt. The current method for performing one of these tests, also called a polymerase chain reaction test, can take eight hours or longer, requires results to be sent to a lab, and is prohibitively expensive in many cases.

There are times when much more aggressive measures might make sense, regardless of implications for costs or civil liberties, experts told me. But this outbreak doesn't appear to be one of them. Ebola doesn't spread easily, through the air. The only way you get Ebola is by coming into contact with bodily fluids from somebody who has the disease. That makes it a very different kind of threat.

Of course, it’s not clear that active airport screening and quarantines would be enough to keep a more highly communicable, airborne disease from coming to the U.S. Public health officials ramped up airport screening during the bird flu and it didn’t seem to do much good. “I think that thermal screeners help people feel safe,” Noreen Hynes, an infectious disease expert at Johns Hopkins, told DefenseOne.

If anything, Ebola’s arrival in the U.S. should be a reminder of what the U.S. and other developed countries should be doing to protect themselves—sending more aid overseas. In the short-term, it can help afflicted countries contain the outbreak, by providing them with basic supplies (like gloves) and personnel necessary to treat the infected. In the long-term, such investments can help those countries build the necessary infrastructure—and recruit the right professionals—to fight outbreaks in the future. Julia Belluz and Steven Hoffman recently sketched out what such an effort would entail in an article for Vox.

As Markel, who is editor-in-chief of the Milbank Quarterly, writes in an upcoming issue:

Long after Ebola is contained, the wealthier nations (and those fortunate enough to live in them) must get to work in righting the unacceptable injustice of a continent where health care is inaccessible for too many; where fresh, running water is scarce; and where electrification and modern roadways are inadequate.  Such infrastructural problems make the overwhelming majority of epidemics worse and undermine efforts to fight them. This is precisely what we are seeing in western Africa today. 

In the long run, the best strategy for stopping epidemics like Ebola from coming to the U.S. is to contain them within the countries where they start.

Update: I just heard back from Chris Woods, an infectious disease specialist at Duke University. Like the other experts I consulted, he was skeptical that airport screening would have caught this case. But he was less dismissive of the idea overall: 

There is potentially a long incubation period and, as evidenced by the case in Dallas, an incubating patient can pass through such active surveillance.

Personally, I still believe there is some benefit to active screening at airport disembarkation because that is the last opportunity to limit exposures.  The costs and benefits need to be considered carefully though.

Later on Wednesday, a member of Porter's staff e-mailed to provide more details of what the senator has in mind:

Portman has called for “active screenings” at U.S. ports of entry so that all passengers from countries with known outbreaks of Ebola are questioned as they arrive. Just as incoming international passengers are now asked where they have been, whether they are bringing in fruits or vegetables or have been in contact with livestock, travelers from West Africa would be asked if they were in contact with someone with Ebola or someone displaying symptoms of Ebola, or if they demonstrated any symptoms.

If the answer is yes or suspicions are raised, the passenger would be referred to CDC officials for additional questioning, medical screening, and quarantine, if necessary. Active screening would have given the CDC the ability to quarantine the patient upon his entrance to the U.S. which would have prevented him from coming into contact with additional people before he entered the Texas hospital four days later. Furthermore, even if the CDC chose not to quarantine him, the knowledge that the patient had traveled from Liberia and had come into contact with others with Ebola could have prevented the Texas hospital from initially discharging the patient after his initial examination.

This actually sounds more effective than temperature screening, though I'm not sure how different it is from current procedures. I'll update again if I learn more.