Ebola outbreak: The limitation of airport screenings

The arrival in Dallas of Thomas Duncan, the first person to be diagnosed with Ebola in the U.S., has raised concerns over air travel's potential to spread a deadly disease across countries and continents.

Duncan's case has prompted some U.S. lawmakers to demand screening procedures at U.S. airports, while others, like Louisiana Governor Bobby Jindal, have called on the government to impose a travel ban from Ebola-stricken countries. 

The case also illustrates the possible limitations of airport screening along with its reliance on passengers to follow the honour system.

"We do rely on people to be honest," said Amesh Adalja, an infectious disease physician at the University of Pittsburgh Medical Centre. "When someone isn't truthful about their contact with Ebola patients, we are limited by that."

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So far, because Ebola is not an airborne disease and can only be transmitted by direct contact with the body fluids of a person who is sick, the World Health Organization and the Center for Disease Control have been opposed to any kind of travel ban. 

During the outbreak of SARS in 2003, a disease that is spread more easily by airborne transmission like coughing, the risk of contracting that disease in an aircraft was found to be very low, WHO said. 

It also said that the risk of contracting Ebola from a plane is the same as contracting it in any confined space, including a movie theatre, bus, train or at the office.

The Ebola virus can be destroyed by disinfectants, but it can also survive on contaminated surfaces outside an infected person for several hours, some studies have found.

In West African countries like Liberia, Sierra Leone, Guinea and Nigeria, departing passengers are subject to exit screening, which includes taking a person's temperature multiple times prior to them boarding an aircraft. Taking the temperature more than once increases the likelihood of detecting a fever, one of the symptoms of Ebola. 

Screeners can use different types of thermometers, the most common being ones that take the temperature through the ear or that is pointed at the individual like a gun. Thermal full-body scanners have been used in the past, including at some Asian airports during the SARS epidemic. 

But taking an individual's temperature is hardly a foolproof way to detect whether someone has Ebola, as the symptoms for the disease may not develop for days. This means an infected individual may not show any signs of fever. 

In Duncan's case, his temperature had been taken three times at the airport, and all his readings were considered to be within normal levels.

The effectiveness of screening has been questioned by some researchers. Last year Dr. Kamran Khan, an infectious diseases specialist at Toronto's St. Michael's Hospital, released a study that suggested airport screening for disease control rarely makes sense.

"In most situations, screening doesn't make sense. In a handful of situations, it may be justifiable," Khan told the Canadian Press last year. "And if you are going to consider screening, doing it as people leave the source area is a much simpler and a much more efficient way of doing it than when people arrive" somewhere.

The research, based on a study of air travellers departing from Mexico in the early days of the 2009 H1N1 flu pandemic, found that screening was a poor use of resources.

"The fever-screening instruments run low and aren't that accurate," infection control specialist Sean Kaufman, president of Behavioral-Based Improvement Solutions, a bio-safety company in Atlanta, told Reuters.

"And people can take ibuprofen to reduce their fever enough to pass screening, and why wouldn't they? If it will get them on a plane so they can come to the United States and get effective treatment after they're exposed to Ebola, wouldn't you do that to save your life?"

Other problems arise when connecting airports do not screen. For example, Kaufman said he flew from Monrovia to Casablanca to London to Atlanta. He was fever-screened in Monrovia and Casablanca, but not London's Heathrow, he said, and not when he arrived in Atlanta.

"At Heathrow, there were no questions about where I had come from," he said. "I offered the information to the official in Atlanta, and he said, 'Thank you. Be safe.'"

While Adalja, the infectious disease doctor, believes exit screening can be effective, he said entry screening is "like finding a needle in a haystack. A lot of false positives. Different strategy than exit screening which is to prevent people from leaving."