Sunday, July 28, 2013

Head ‘Em Off At The Passenger Gate?


Scheduled airline traffic around the world, circa June 2009 – Credit Wikipedia


For every complex problem there is an answer that is clear, simple, and wrong. - H. L. Mencken


# 7522


With MERS-CoV (along with H7N9 & H5N1) still making headlines, this week a new poll indicates that at least 80% of respondents supported the screening of inbound airline passengers from affected countries for this emerging virus.


A Reuters story this week (see Support high for travel screening to stem MERS spread: poll) has the details (excerpt below).


More than 80 percent of people questioned in developed countries said inbound travelers from countries with cases of MERS should be screened for the illness. The number rose to 90 percent in less industrialized countries.


Support was highest in China, Indonesia and Saudi Arabia, where the illness has been reported, and Italy, which has also been affected, as well as in Australia, Canada and Argentina.


While an understandable reaction by the public, there is scant evidence to suggest that screening passengers would do much, if anything, to prevent the entry of a viral illness into a country.


It’s not that it hasn’t been tried.  It has. But the success rate has been, well . . .  dismal.


The world’s airlines carry 2.6 billion passengers each year, on more than 17 million flights.  And as the graphic at the top of this post indicates, millions of these are international flights.


With most viral diseases having an incubation period that ranges from a couple of days to a week or longer, someone who is newly infected with a virus could easily change planes and continents several times before ever they ever show signs of illness.



And as we saw during the 2009 H1N1 pandemic – even those who are symptomatic will often go to great lengths to get to their destination (see Vietnam Discovers Passengers Beating Thermal Scanners).


In April of 2012, in EID Journal: Airport Screening For Pandemic Flu In New Zealand, we looked at a study that found the screening methods used at New Zealand’s airport were inadequate to slow the entry of the 2009 pandemic flu into their country, detecting less than 6% of those infected.


Admittedly, New Zealand did not employ thermal scanners.  But countries that did, didn’t fare much better.



Thermal Scanner – Credit Wikipedia


In December of 2009, in Travel-Associated H1N1 Influenza in Singapore, we saw a NEJM Journal Watch article on of a new study that had been published, ahead of print, in the CDC’s  EID Journal  entitled:


Epidemiology of travel-associated pandemic (H1N1) 2009 infection in 116 patients, Singapore. Emerg Infect Dis 2010 Jan; [e-pub ahead of print]. Mukherjee P et al

Travel-Associated H1N1 Influenza in Singapore

Airport thermal scanners detected only 12% of travel-associated flu cases; many travelers boarded flights despite symptoms.


In Japan: Quarantine At Ports Ineffective Against Pandemic Flu  I wrote about a study that suggests between asymptomatic or mild infections, and a silent incubation period of several days, there wasn’t much chance of long-term success.


For every person identified, and quarantined, by port authorities  - researchers estimate 14 others infected by the virus entered undetected.


This is a topic that Helen Branswell of the Canadian press has written about often, including last April in:


Airport disease screening rarely worthwhile, study suggests

Helen Branswell, The Canadian Press
Published Wednesday, April 10, 2013 10:11AM EDT


Despite little evidence to suggest that passenger screening would be effective, many governments will probably find it difficult not to be seen at least making the attempt.


On a slightly positive note, while they may not stop a virus, passenger screening might provide some interesting surveillance data.


But practically, as way to keep a pandemic virus from entering a country, it has a low probability of success.


The place to try to stop the next pandemic is not at the inbound passenger gate, but in the places around the world where they are likely to emerge.


Which makes the funding and support of international public health initiatives, animal health initiatives, and disease surveillance hugely important, no matter where on this interconnected globe you happen to live.