Thermal Scanner – Credit Wikipedia
# 7109
While one of the first visible public health reactions we often see whenever a novel disease outbreak occurs somewhere in the world are the setting up of `fever screenings’ at airports, Helen Branswell brings us a report this morning on the limited benefits that these sorts of operations provide.
Airport disease screening rarely worthwhile, study suggests
Helen Branswell, The Canadian Press
Published Wednesday, April 10, 2013 10:11AM EDTTORONTO -- A new study suggest airport screening for disease control rarely makes sense, but if it's undertaken, it should be done at the source of the outbreak.
The researchers say the screening of passengers leaving via a few key airports near the epicentre of an outbreak is a better approach than having hundreds of airports around the world screen arriving passengers.
Those with good memories may recall that in 2009 Helen wrote about another study that found thermal scanning technology wanting (see Fluing The Friendly Skies).
Studies show little merit in airport temperature screening for disease
Monday, 16 February 2009 - 11:58am.
By Helen Branswell
TORONTO — Using temperature scanners in airports to try to identify and block entry of sick travellers during a disease outbreak is unlikely to achieve the desired goal, a report by French public health officials suggests.
Both articles are well worth reading in their entirety.
Scheduled airline traffic around the world, circa June 2009 – Credit Wikipedia
The world’s airlines carry 2.6 billion passengers each year, on more than 17 million flights. And as the map above indicates, millions of them are international flights.
With most viral diseases having an incubation period of several days or longer, someone who is newly infected with a virus could easily change planes and continents several times before showing their first signs of illness.
And as we saw during the 2009 H1N1 pandemic, passengers anxious to get home during a crisis will often go to great lengths to hide the fact that they might be infected (see Vietnam Discovers Passengers Beating Thermal Scanners).
Last July, in MIT: Contagion Dynamics Of International Air Travel we looked at a study appearing in PloS One, that simulated the early spread of a pandemic virus via air travel and ranked U.S. airports based on how much they contributed to the spread of the illness.
An excerpt from a report that appeared in MIT News.
New model of disease contagion ranks U.S. airports in terms of their spreading influence
Airports in New York, Los Angeles and Honolulu are judged likeliest to play a significant role in the growth of a pandemic.
Kennedy Airport is ranked first by the model, followed by airports in Los Angeles, Honolulu, San Francisco, Newark, Chicago (O'Hare) and Washington (Dulles). Atlanta's Hartsfield-Jackson International Airport, which is first in number of flights, ranks eighth in contagion influence. Boston's Logan International Airport ranks 15th.
All of which begs the question, can we really screen, identify, and isolate infectious airline passengers before they can spread a pandemic virus?
Sadly, the evidence to date has not been very encouraging.
Last April, 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.
New Zealand did not employ thermal scanners, although countries that did, didn’t fare much better.
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.
A dismal success rate.
Despite the aggressive use of thermal imagers, passenger interviews, and other screening methods - Japan found it impossible to prevent entry of the H1N1 virus into their country during the early days of the 2009 pandemic.
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.
Politically, and in terms of reassuring the public, the screening of passenger arriving at airports and other points of entry probably has a lot of merit. And they can provide valuable surveillance information as well.
But practically, as an effective way to keep an emerging virus out of a country, studies continue to show just how unlikely that outcome really is.
