Why Airport Screening Can’t Stop MERS, Ebola or Avian Flu

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

 

# 9132

 

Whenever there is an outbreak of a potentially deadly, highly infectious disease somewhere in the world - and cases begin to show up elsewhere as a result of modern air travel -  the question is always raised:

Why can’t we stop infected individuals from entering the country by screening at airports and the border?

 

It is, after all, an idea that is promoted by the manufacturers of thermal scanning devices, and often pulled out of the rabbit hat by governments around the world when a disease threat appears. 

 

During the SARS epidemic of 2003, the H1N1 pandemic, and more recently with MERS and H7N9, many countries have employed fever scanning technology on incoming passengers.

 

Thermal Scanner – Credit Wikipedia

 

Last year, in Head ‘Em Off At The Passenger Gate?, we looked at a Reuters story called Support high for travel screening to stem MERS spread: poll, that found:

 

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.

 

The problem is, while the technology can detect (most) people with fevers, their track record of detecting and preventing infected individuals from entering a country has been only slightly better than dismal.  The biggest obstacle being:  not everyone who is infected with the fear du jour will exhibit a fever.

 

• Some may be silently incubating the virus, and will become symptomatic hours or days after arrival
• Others may have other symptoms, but no fever
• Some may be taking antipyretics (fever reducers) to ease symptoms or evade detection
• And some may simply be asymptomatic carriers of the virus.

And since MERS, Avian Flu, and Ebola outbreaks don’t happen in a vacuum – and there are likely to be a far greater number of passengers less dire fever producing infections (colds, flu, WNV, teething babies, etc.) – trying to determine who to quarantine and who to let through becomes a nightmare.

A strict `any fever=no entry’ policy would quickly turn any busy airport or entry point into a shambles, cause massive travel delays for everyone, and incur great economic costs. 

All the while `silent’ infections would  pass through undetected.

 

We know this because previous attempts to interdict SARS and H1N1 using airport screeners and/or thermal scanners have been well studied. In 2010, in  Japan: Quarantine At Ports Ineffective Against Pandemic Flu, I wrote about a study that found 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.

 

In April of 2012, in EID Journal: Airport Screening For Pandemic Flu In New Zealand, we looked at a study that found that 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.

 

Unlike some other countries in 2009, New Zealand did not employ thermal scanners, which look for arriving passengers or crew with elevated temperatures.  But even countries that employed thermal scanners and far more strict interdiction techniques during the summer of 2009 failed to keep the flu out.

 

Since there is nothing worse than being sick away from your own country and your own doctor, to little surprise in Vietnam Discovers Passengers Beating Thermal Scanners, we saw evidence of flyers taking fever-reducers to beat the airport scanners in order to get home.

 

In December of 2009, in Travel-Associated H1N1 Influenza in Singapore, I wrote about a a study in the CDC’s  EID Journal  entitled: Epidemiology of travel-associated pandemic (H1N1) 2009 infection in 116 patients, Singapore that determined that airport thermal scanners detected only 12% of travel-associated flu, and that many travelers boarded flights despite already experiencing symptoms.

 

And in June of 2010 CIDRAP carried a piece on a study of thermal scanners in New Zealand in 2008 (before the pandemic) presented at 2010’s ICEID called Thermal scanners are poor flu predictors.

 

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.

 

It should be stressed that there is a role for screening passengers departing a known outbreak location for fever or other signs of illness, and that passengers who are visibly ill should always be attended to, and isolated if necessary. 

 

The WHO’s advice in their August 18th Statement on travel and transport in relation to Ebola virus disease (EVD) outbreak.

Affected countries are requested to conduct exit screening of all persons at international airports, seaports and major land crossings, for unexplained febrile illness consistent with potential Ebola infection. Any person with an illness consistent with EVD should not be allowed to travel unless the travel is part of an appropriate medical evacuation. There should be no international travel of Ebola contacts or cases, unless the travel is part of an appropriate medical evacuation

 

And finally,  a statement  I wrote about last June in  WHO: IHR Committee Statement On Thermal Screening For MERS-CoV, which said:

 

Finally, the Committee indicated that there was no solid information to support the use of thermal screening as a means to stop or slow the entry of MERS-CoV infections, and that resources for supporting such screening could be better used to strengthen surveillance, infection control and prevention or other effective public health measures.

 

Airport screening isn’t useless, as it can identify acutely ill individuals when they are likely to be the most contagious so they can be promptly isolated,  and it can provide important surveillance information. And it might even help slow the rate of entry of an emerging disease into a region, allowing additional time to mount public health interventions. 

 

But as far as preventing an infectious disease like MERS, Ebola or Avian Flu from entering this - or any other country -  airport screening is apt to prove a major disappointment.

Hong Kong CHP Takes Notice Of Taiwan’s H7N9 Case

Thermal Scanner – Credit Wikipedia

 

# 8118

 

 

As you might expect, today’s big story out of Taiwan (see Taiwan CDC Reports Second Imported H7N9 Case) has not escaped the notice of the public Health Officials in Hong Kong.  The following statement has been posted on their http://www.info.gov.hk website, which also contains details on Hong Kong’s border security measures designed to identify and isolate potential carriers of the virus.

 

First, the statement, then I’ll return with a bit more on the value and history of thermal screening for disease.

 

 

CHP closely monitor a human case of avian influenza A(H7N9) in Taiwan

The Centre for Health Protection (CHP) of the Department of Health (DH) tonight (December 31) noted a confirmed human case of avian influenza A(H7N9) affecting a man aged 86 in Taiwan.

The patient, who lives in Jiangsu Province in Mainland China, travelled to Taiwan on December 17. He had onset of symptoms including loss of appetite and chest discomfort since December 19. He sought medical consultation from a local hospital on December 24. His specimen tested positive for the avian influenza A(H7N9) virus upon testing by the health authority in Taiwan today. He is currently admitted for further management.

"Locally, enhanced disease surveillance, port health measures and health education against avian influenza are ongoing. We will remain vigilant and maintain liaison with the World Health Organization (WHO) and relevant health authorities. Local surveillance activities will be modified upon the WHO's recommendations," a spokesman for the DH remarked.

All border control points (BCPs) have implemented disease prevention and control measures. Thermal imaging systems are in place for body temperature checks of inbound travellers. Suspected cases will be immediately referred to public hospitals for follow-up investigation.

Regarding health education for travellers at BCPs, distribution of pamphlets, display of posters in departure and arrival halls, in-flight public announcements, environmental health inspection and provision of regular updates to the travel industry via meetings and correspondence are all proceeding.

"Travellers, especially those returning from avian influenza A(H7N9)-affected areas and provinces with fever or respiratory symptoms, should immediately wear masks, seek medical attention and reveal their travel history to doctors. Health-care professionals should pay special attention to patients who might have contact with poultry, birds or their droppings in affected areas and provinces," the spokesman advised.

(Continue . . . )

 

 

Hong Kong has recently seen two imported cases of H7N9 themselves, and with the traditional peak of the `bird flu season’ still ahead, finds itself – like Taiwan – is very much on the front lines against this emerging virus.

 

Since fever is often a hallmark of infection, thermal imaging has been promoted as a way to protect the public and (hopefully) delay introduction of a virus into a country during a pandemic. Unfortunately, these checks haven’t produced much in the way of compelling results in the past. 

 

The problem is, not everyone who is infected will exhibit a fever.

 

• Some may be silently incubating the virus, and will become symptomatic in another 24-48 hours
• Others may have other symptoms, but no fever
• Some may be taking antipyretics (fever reducers) to ease symptoms or evade detection
• And some may simply be asymptomatic carriers of the virus.

 

Added to these, scanners can be foiled by other factors including the consumption of hot beverages or alcohol, pregnancy, menstrual period or hormonal treatments.  All of which can increase the external skin temperature and cause a false positive.

 

Inversely, intense perspiration or heavy face make-up can have a cooling effect on the skin temperature which can cause a false negative.

 

Over the years we’ve looked at a number of thermal screening studies that have tried to quantify their value.  A few highlights include:

 

In April of 2012, in EID Journal: Airport Screening For Pandemic Flu In New Zealand, we looked at a study that found that 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.

 

Unlike some other countries in 2009, New Zealand did not employ thermal scanners, which look for arriving passengers or crew with elevated temperatures.  But even countries that employed thermal scanners and far more strict interdiction techniques during the summer of 2009 failed to keep the flu out.

 

Since there is nothing worse than being sick away from your own country and your own doctor, to little surprise in Vietnam Discovers Passengers Beating Thermal Scanners, we saw evidence of flyers taking fever-reducers to beat the airport scanners in order to get home.

 

In December of 2009, in Travel-Associated H1N1 Influenza in Singapore, I wrote about a a study in the CDC’s  EID Journal  entitled: Epidemiology of travel-associated pandemic (H1N1) 2009 infection in 116 patients, Singapore that determined that airport thermal scanners detected only 12% of travel-associated flu, and that many travelers boarded flights despite already experiencing symptoms.

 

And in June of 2010  CIDRAP carried a piece on a study of thermal scanners in New Zealand in 2008 (before the pandemic) presented at 2010’s ICEID called Thermal scanners are poor flu predictors.

 

None of which is to suggest that Hong Kong shouldn’t try to interdict infected travelers at the border, because even if the success rate is low, there may be some value in trying to limit the number of infected persons arriving into a country, particularly during the opening days and weeks of an outbreak.

 

But no one should be over-comforted by the thought of thermal scanners deployed at borders or airport terminals, as their impact on the spread of any infectious disease is likely to be limited.

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.

Pathogens At the Gate

Thermal Scanner – Credit Wikipedia

 

# 6593

 

While there are no indications that the coronavirus detected recently in the Middle East has spread beyond the first two cases, some places around the world are taking this threat very seriously.

 

For example, local media is reporting that thermal scanners have been deployed at the Ninoy Aquino International Airport in the Philippines in an attempt to screen arrivals from the Middle East for possible infection.

 

Whenever a novel virus appears, people’s thoughts understandably turn to a pandemic scenario, even though experience has shown that most emerging viruses don’t have the `legs’ to spark a global epidemic (see Novel Viruses & Chekhov’s Gun).

 

Nevertheless, history tells us that pandemics come along several times each century, and another pandemic is all but inevitable.

 

And so the world’s attention this week has quite naturally focused on the novel coronavirus that killed one man in Saudi Arabia last July and has a Qatari man currently hospitalized in London.

 

Memories of the SARS outbreak in 2002 and 2003 remain vivid, particularly in Asia, where the virus hit hardest.

 

Fortunately, while there is still much we don’t know about this emerging pathogen, there are no immediate signs that this virus poses a pandemic threat.

 

While we may not know when - or which virus - will spark the next global health crisis, we have pretty good idea how it will arrive in most countries.

 

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 change planes and continents several times before showing their first signs of illness.

 

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 examined 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.

  

Proving that `there’s no place like home’ during a global crisis, in Vietnam Discovers Passengers Beating Thermal Scanners, we saw evidence of passengers taking fever-reducers to beat the airport scanners in a desperate attempt to get home.

 

In December of 2009, in Travel-Associated H1N1 Influenza in Singapore, I blogged on a NEJM Journal Watch article on of a new study that has 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 June of 2010  CIDRAP carried this piece on a study of thermal scanners in New Zealand in 2008 (before the pandemic) presented at 2010’s ICEID.

 

Thermal scanners are poor flu predictors

Thermal scanners for screening travelers do moderately well at detecting fever, but do a poor job at flagging influenza, according to researchers from New Zealand who presented their findings today at the International Conference on Emerging Infectious Diseases (ICEID) in Atlanta.

 

And in early 2009, Helen Branswell penned an article for the Canadian Press, that stated:

 

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.

(Continue. . .)

 

 

The evidence is pretty clear.

 

With the technology of today, coupled with likelihood of having many pre-symptomatic and asymptomatic carriers, there isn’t much hope to identify more than a fraction of infected travelers.

 

As far as the risk of catching a pandemic flu virus while a passenger on an airliner, in May of 2010 we saw a study that appeared in the BMJ that looked at that very topic (see BMJ: Flu Transmission Risks On Airplanes)

 

BMJ 2010;340:c2424

Research

Transmission of pandemic A/H1N1 2009 influenza on passenger aircraft: retrospective cohort study

Conclusions

A low but measurable risk of transmission of pandemic A/H1N1 exists during modern commercial air travel. This risk is concentrated close to infected passengers with symptoms. Follow-up and screening of exposed passengers is slow and difficult once they have left the airport.

 

Another study, conducted by researchers at UCLA and published in BMC Medicine in late 2009:

 

Calculating the potential for within-flight transmission of influenza A (H1N1)

Bradley G Wagner, Brian J Coburn and Sally Blower^*

Results

The risk of catching H1N1 will essentially be confined to passengers travelling in the same cabin as the source case. Not surprisingly, we find that the longer the flight the greater the number of infections that can be expected. We calculate that H1N1, even during long flights, poses a low to moderate within-flight transmission risk if the source case travels First Class.

(Continue . . .)

 

 

While there will likely be intense public clamor to try to block the entry of a pandemic virus into this, or any other country, the truth is – it is highly unlikely that it will work.

Areas that receive a very small number of arrivals might be able to institute a quarantine system (see Can Island Nations Effectively Quarantine Against Pandemic Flu? ), but even then the ability to identify and isolate infected travelers won’t be 100%.

 

Still, even if the success rate is likely to be low, there may be some value in trying to limit the number of infected persons arriving into a country, particularly during the opening days and weeks of an outbreak.

 

The more introductions of a virus into a population, the more points it will have from which to spread.

 

Since it takes months to produce and deploy a vaccine, and time to prepare a society to deal with a pandemic, any delaying action that can reduce the speed and spread of the virus has value.

 

The takeaway from all of this is that we ignore global healthcare and infectious disease outbreaks – even in the remotest areas of the world – at our own peril.

 

Vast oceans and extended travel times no longer offer us protection, and there is no technological shield that we can erect that would keep an emerging pandemic virus out.

 

The place to try to stop the next pandemic is not at the 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 ever so important, no matter where on this globe you happen to live.