TORONTO – Canadian research has pioneered a new formula that could be used around the world to help decipher when to screen passengers at airports for disease control.
Screening airports for potential disease outbreaks has been seen as disruptive to travel and the economy. But a St. Michael’s Hospital researchers says that officials can ask themselves a few key questions to help them select only a handful of airports to screen departing passengers. That’s the key to successful monitoring, he says.
Infectious disease expert Dr. Kamran Khan developed the tool after analyzing all international airplane traffic at the onset of 2009’s H1N1 pandemic.
He scoured the air traffic flights of nearly 600,000 people who flew out of Mexico in May 2009 when H1N1 started.
He says exit screening at only a handful airports could have stopped the swine flu pandemic, which swept most of the globe that year.
“What we identified was that you could actually assess 90 per cent of all the people who would have been at risk of carrying H1N1 outside of Mexico to other countries simply by intervening at eight airports,” Khan told Global News.
Read more: Canadian researchers develop disease outbreak surveillance
It’s catching the outbreak before passengers board planes that matters: if all passengers at risk of H1N1 were screened as they left one of Mexico’s 36 airports, the disease could have been stopped in its tracks from crossing international borders.
But if passengers were screened upon landing, passengers at 82 airports and in 26 countries would have to be screened.
The tool is based on a three-pronged approach: is the country where an outbreak has started taking on effective exit screening? If not, is this city receiving direct flights from the source of an outbreak? And what is the incubation period of a disease?
“One never waits for a fire to spread before putting it out. It only makes sense to intervene as early as possible right at the source,” Khan said.
“The same principle applies to infectious disease outbreaks. To prevent or slow the spread of infectious disease, the most efficient strategy is to control an outbreak at its source,” he said.
Screening passengers as they enter a country – which is in place in some countries – isn’t as useful, as people leaving an outbreak site have hours on planes and airports mingling with others.
If all international travellers were screened upon arrival, 116 people would have to be screened for every traveller exposed to H1N1. That makes for 67.3 million travellers at 1,111 international airports.
Outbreak monitoring currently in place relies on thermal screening and self-reported information. Khan says these systems have their flaws.
Keep in mind, most flights are no longer than 12 hours. The incubation period for H1N1, and most influenzas, is about two days. Up to 91 per cent of people potentially carrying the swine flu virus out of the country were on flights about six hours long.
In that short window of time, the virus flies under the radar, it being too soon to notice any symptoms of illness.
On the heels of the SARS outbreak in 2003, 194 countries joined a global treaty to protect against the spread of infectious disease but with a promise that doing this wouldn’t put unnecessary restrictions on international travel and trade.
It’s been difficult figuring out how to officials can balance these for health safety and economic growth.
International cooperation needs to be in place to make this approach work, Khan says.
Poor countries where most outbreaks may start, for example, will need the help of affluent nations to fund the expertise and equipment for screening.
Khan points to the current H7N9 bird flu in China. The United States’ Centers for Disease Control has been actively providing diagnosis and support in an attempt to stifle the influenza.
Khan’s research doesn’t recommend a screening procedure.
His complete findings were published in the May issue of the Bulletin of the World Health Organization.
beatrice.politi@globalnews.ca
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