02/22/2015 11:42 EST | Updated 04/24/2015 05:59 EDT

To Prevent the Spread of Ebola, We Need Better Airport Screening

Ebola Zaire virus
SCOTT CAMAZINE via Getty Images
Ebola Zaire virus

Anyone who has watched the captivating program, Border Security knows thousands of men and women are this country's first line of defense against international threats. These individuals work tirelessly -- and as the show reveals, calmly -- to keep out a plethora of potential problems from illegitimate workers to illegal drug smuggling to weapons. Without them, the country would be far less safe.

While preventing these social issues is fairly simple, when it comes to microbiological protection of health, the process is somewhat more complex. The Canada Border Services Agency works with the Public Health Agency of Canada to ensure infections are kept out of the country, as prescribed by the Quarantine Act. For the most part, this part of the screening regimen is invisible and causes no impedance. But last year, during the height of the Ebola worry, the Public Health Agency of Canada strengthened its use of the Act to help prevent any importation of the virus.

The practice did not go forward without some controversy with some suggesting it was a waste of time. This was partly due to the nature of the procedure, which naturally focused on the history of travel as well as the current health state. Issues such as lying about one's past movements and lack of symptoms could render the screening ineffective and the virus would have little trouble crossing the border. Indeed, over the course of last year, several individuals were put into isolation due to fears of having the virus. Yet as of today, no cases have appeared on Canadian soil.

The other problem with screening is the issue of a pathogen's incubation period, which is the time between exposure and onset of symptoms. For Ebola and several other viruses, this can be days if not weeks. Unless the timing is perfect -- symptoms appear on the plane -- the likelihood of catching the virus is quite low.

The compiled information suggests airport screening may not be effective. But this may be simply due to the rareness of the situation. Though millions of people cross the border every single year, only a handful might have come from a suspect region and of those, even fewer would have had any potential exposure. Finally, of those exposed, few to none would exhibit symptoms. Unfortunately, carrying out a more comprehensive study as one might do in the clinical world is not an option.

But last week, an international trio of researchers provided an in-depth look at the potential of airport screening using not human but mathematical models. They attempted to identify the effectiveness of the border protection measures against six different pathogens, pandemic influenza H1N1, avian influenza H7N9, SARS, Ebola and two others making global health headlines, the Middle East Respiratory Syndrome (MERS) and a virus related to Ebola, Marburg.

The team looked at two different scenarios; a person with symptoms and one without. They then took these modeled cases through several points of observation including departure screening, activities on the plane, and at the destination's border. Based on research from previous outbreaks, fixed values could be used for exposure risk and incubation period. But when it came to behaviour, the team had to make an estimate, particularly the likelihood of a traveler being honest on a questionnaire -- which was estimated at 25 per cent. The final parameter was the extent of the epidemic, whether emerging or stable.

At that point, the model was put into place with three possible screening methods. One was detection of fever (symptoms), the other was an exposure risk questionnaire, and the third was both. For robustness of data, each simulation looked at 50 infected individuals with a range of incubation times and also honesty on the questionnaire form.

After repeating the simulation 2,000 times, the authors had enough information to provide some conclusions. First and foremost, screening worked but not entirely well. Not a single measure would be able to detect more than 60 per cent of cases meaning the majority of people would be able to pass through both departures and arrivals without any concern. For those who are flagged, fever was the most likely means for detection. That being said, the combination of fever assessment and questionnaire was better than either one alone.

Taking a closer look at the data revealed the best results came from infections with short incubation times, such as the flu. When that time increased, the effectiveness dropped. In addition, the actual awareness of the public to the nature of an epidemic was also important. If emerging, few might know the risk factors and could end up inadvertently falsifying documents. In this case, fever checks would be the main method of detection. In contrast a stable epidemic would likely result in more people being identified through questionnaires.

The authors conclude screening are not solely effective or ineffective but depend on a number of factors outside of the control of border officials. At the policy level, each pathogen needs to be given attention and procedures designed for its unique properties. At the human level, these measures need to be accompanied by awareness campaigns to ensure the public knows of the infectious threat and also how lying can affect not only themselves but others.

There is also one more point the authors make and this goes to the heart of the screening process. For a public concerned about the introduction or emergence of a particular pathogen such as Ebola, an increased security presence is always welcome. Though the actual numbers of picked up by these measures may be low, from a public confidence perspective, the prevention of even one case from coming into the country and causing potential havoc is well worth the time and effort.


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