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04/10/2013

As bird flu cases mount, a new tool for containing global outbreaks

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Source: St. Michael's Hospital

Another day, another handful of new H7N9 cases, another death to report in eastern China.

The new bird flu strain continues to puzzle and alarm health officials in China and around the world. But thankfully, H7N9 isn't spreading easily between people -- yet.

Public health authorities are tightly crossing their fingers that the virus fails to mutate into a more dangerous form and will eventually just sputter out. The fear is that it will evolve into something more infectious -- like H1N1, which popped up in Mexico and caused a pandemic in 2009.

Luckily, H1N1 wound up being a pretty wimpy virus and caused mostly just mild disease -- but from the looks of it, an H7N9 pandemic would prove much more devastating.

You can bet public health officials worldwide are already preparing for that eventuality, which is why there is no better timing for this new paper, published in the Bulletin of the World Health Organization.

The paper comes from a group of scientists led by Dr. Kamran Khan, an infectious disease physician at St. Michael's Hospital and founder of BioDiaspora, a really interesting program that uses global flight patterns to predict the spread of new infectious diseases. (Khan spoke to the Toronto Star earlier this week about the likelihood of an H7N9-infected traveller from China coming to Canada -- for now, the chances of that are pretty low).

When outbreaks hit, public health officials have to make difficult but necessary decisions to prevent a virus from spreading further. They might consider airport screening, for instance -- but such measures should not be taken lightly, because they are hugely disruptive and require major resources.

So such actions need to have a strong scientific basis -- and that's where Khan's paper comes in. Looking at the 2009 H1N1 pandemic, Khan and his co-authors analyzed flight itineraries for more than 580,000 at-risk travellers who flew out of Mexico in May 2009.

They concluded it is much more efficient to screen passengers exiting an outbreak country than those arriving at their destination airports. According to Khan's estimates, all at-risk travellers during H1N1 could have been assessed with exit screening at Mexico's 36 international airports.

And 90 per cent of all at-risk travellers worldwide could have been captured by screening at just six of Mexico's largest international airports, coupled with targeted screening at two airports in Shanghai and Tokyo.

On the other hand, trying to screen those same travellers when they arrived at their destination airports would have required setting up checkpoints at 82 international airports in 26 countries.

And screening all international travellers at their arrival destinations would have been staggeringly difficult. During the H1N1 pandemic, this would have meant screening 67.3 million grumpy travellers at 1,111 airports -- and for every one person who actually had exposure to H1N1, 116 people would have been unnecessarily screened.

Using their findings, Khan and his co-authors developed a basic tool to help public health officials decide whether, and how, to set up airport screening. The tool takes three things into account: 1) whether there is effective exit screening at the source of the outbreak 2) whether a city receives direct flights from the outbreak country 3) the incubation period of the disease.

"One never waits for a fire to spread before putting it out," Khan said in a press release. For now, the H7N9 situation is just a few dozen sparks in eastern China -- let's hope it doesn't become a flame we have to snuff out.

Update: Canadian Press reporter Helen Branswell has written a great article about Khan's study, which has now been posted on the Toronto Star's website here.

Jennifer Yang is the Star’s global health reporter. She previously worked as a general assignment reporter and won a NNA in 2011 for her explanatory piece on the Chilean mining disaster. Follow her on Twitter: @jyangstar

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