EID Journal: Evaluating Border Entry Screening for Infectious Diseases in Humans

Thermal Scanner – Credit Wikipedia

 

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

 

# 9276

 

Over the years I’ve probably written about the futility of trying to prevent entry of infectious diseases into a country by airport or border screening at least a dozen times.   A few recent examples include:

 

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

MERS: The Limitations Of Airport Screening

Head ‘Em Off At The Passenger Gate?

It is not the message that most people want to hear. But the truth is we possess no technology that can reliably detect someone who is infected – but not yet overtly symptomatic – with an infectious disease like influenza, MERS, or Ebola. With luck, you might delay entry of an emerging pandemic virus by a few days or weeks, but even that may be overly optimistic. 

 

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.

 

While fever scans tend to reassure the public, they are easily fooled (see Vietnam Discovers Passengers Beating Thermal Scanners), and non-specific – resulting in a lot of false alarms.  Last June, in WHO: IHR Committee Statement On Thermal Screening For MERS-CoV), we saw the following opinion regarding the effectiveness of thermal screening at airports and borders.

 

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.

 

Yesterday the CDC’s EID Journal posted a detailed perspective, which looks back over earlier attempts with SARS and the 2009 H1N1 influenza virus to interdict infected arrivals through screening. Follow the link to read their reasoning in its entirety.

 

Volume 21, Number 2—February 2015

Perspective

Evaluation of Border Entry Screening for Infectious Diseases in Humans

Linda A. Selvey , Catarina Antão, and Robert Hall

Author affiliations: Curtin University, Perth, Western Australia, Australia (L.A. Selvey, C. Antão); Monash University, Melbourne, Victoria, Australia (R. Hall)

Abstract

In response to the severe acute respiratory syndrome (SARS) pandemic of 2003 and the influenza pandemic of 2009, many countries instituted border measures as a means of stopping or slowing the spread of disease. The measures, usually consisting of a combination of border entry/exit screening, quarantine, isolation, and communications, were resource intensive, and modeling and observational studies indicate that border screening is not effective at detecting infectious persons. Moreover, border screening has high opportunity costs, financially and in terms of the use of scarce public health staff resources during a time of high need. We discuss the border-screening experiences with SARS and influenza and propose an approach to decision-making for future pandemics. We conclude that outbreak-associated communications for travelers at border entry points, together with effective communication with clinicians and more effective disease control measures in the community, may be a more effective approach to the international control of communicable diseases.

<SNIP>

Conclusion

Historically, most attempts at border screening have been ineffectual, as demonstrated by the pandemic spread of SARS and influenza A(H1N1)pdm09 to many countries despite the use of border screening. Modeling and observational studies have indicated that border screening is likely to be unsuccessful in preventing or delaying the entry of such diseases into a country. Border screening generally has high opportunity costs, both financially and in terms of the use of scarce public health staff resources at a time of high need. We conclude that border screening should not be used. Instead, the less costly measure of providing information to arriving travelers is recommended, together with effective communication with local clinicians and more effective disease control measures in the community.

 

Politically, and in terms of reassuring the public, the screening of passenger arriving at airports and other points of entry probably has some benefits.  And it can provide an opportunity to educate arrivals about symptoms, and what to do should they fall ill.

 

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.

UK Statement On Airport Screening For Ebola

Credit UK.gov

 

# 9174

 

Three days ago the UK government was still openly resisting the idea of screening inbound passengers for Ebola symptoms  (see Ebola surveillance and contingency planning ongoing in UK) - but between public and media pressures to `do something’, and seeing the United States and Canada announce targeted enhanced screening (see Airport Screening Fact Sheet) – the decision to go ahead has finally been made.

 

While airport screening may be reassuring to the public, many public health experts question the value of these types of interventions, as they did little to prevent the importation of either SARS or the 2009 H1N1 pandemic virus  (see Why Airport Screening Can’t Stop MERS, Ebola or Avian Flu).

 

Given the limited scope, and targeted nature of these screenings (as they stand today, anyway) – while I don’t expect them to be terribly effective – I don’t view them as being a complete waste of time, either. 

 

It is possible that some symptomatic cases might be detected and isolated before they can spread the disease, and the contact information gleaned from recent travelers to West Africa might be helpful to public health officials.

 

Still, no one should be overly reassured by these measures.  They have a low probability of ultimately preventing Ebola – or any other infectious disease – from entering a country.

 

Here then is the statement from UK.GOV.

 

A statement on the introduction of screening at UK travel destinations has been issued following advice from the Chief Medical Officer.

A Downing Street spokesperson said:

“The UK is continuing to monitor the outbreak of Ebola closely, including the protection of the UK against people travelling here who may be infected.

Airport screening at airports in Liberia, Sierra Leone and Guinea has been in place for some weeks to ensure all passengers leaving affected countries are checked.

Further screening has been kept under review throughout this period and advice from the Chief Medical Officer today is that enhanced screening arrangements at the UK’s main ports of entry for people travelling from the affected regions - Liberia, Sierra Leone and Guinea - will offer an additional level of protection to the UK.

Enhanced screening will initially be implemented at London’s Heathrow and Gatwick airports and Eurostar terminals and will involve assessing passengers’ recent travel history, who they have been in contact with and onward travel arrangements as well as a possible medical assessment, conducted by trained medical personnel rather than Border Force staff. Passengers will also be given advice on what to do should they develop symptoms later.

As the Chief Medical Officer’s advice makes clear, these measures will help to improve our ability to detect and isolate Ebola cases. However, it is important to stress that given the nature of this disease, no system could offer 100% protection from non-symptomatic cases.

It is important to remember that the overall risk to the public in the UK continues to be very low, and the UK has some of the best public health protection systems in the world with well-developed and well-tested systems for managing infectious diseases when they arise. Contingency planning is also underway including a national exercise and wider resilience training to ensure the UK is fully prepared.”

Advice from the Chief Medical Officer

The Chief Medical Officer said:

“In line with international health requirements, exit screening arrangements have already been implemented in the affected countries in west Africa to ensure that any passenger showing signs of Ebola is prevented from leaving the country.

Although the risk to the UK remains low, in view of the concern about the growing number of cases, it is right to consider what further measures could be taken, to ensure that any potential cases arriving in the UK are identified as quickly as possible. Rapid access to healthcare services by someone infected with Ebola is not only important for their health but also key to reducing the risk of transmission to others.

These measures could include a further UK based package of measures to identify and assess the health status of passengers arriving from the affected countries and to ensure that those individuals know what to do should they be taken ill whilst in the UK.

We remain alert and prepared, should an Ebola case be identified here. We have well tested processes in place but anything that means that people are more likely to present early are to be welcomed.”

Airport Screening Fact Sheet

 

# 9168

 

Although it won’t detect asymptomatic carriers of Ebola (the incubation period runs up to 21 days) or those less than forthright about their previous Ebola exposures, the US has announced limited targeted screening of visitors with recent travel history to Liberia, Guinea, or Sierra Leone (see CDC Statement On Airport Screening Of Arrivals From West Africa).

 

While there are some benefits to this type of screening, no one should be overly reassured that this will completely block the entry of Ebola cases into the United States. 

 

Eric Duncan was reportedly asymptomatic when he left Liberia and again when he arrived stateside, only falling ill several days later. So he would have likely passed through this type of screening. Still, even when the benefits may be limited, it is often better to do something rather than nothing.

 

Yesterday the CDC and DHS released a fact sheet outlining the screening process.

 

SCREENING OF TRAVELERS AT AIRPORTS

This fact sheet helps explain the measures the Centers for Disease Control and Prevention (CDC), the Department of Homeland Security’s Customs and Border Protection, and their partners are taking at airports both in the United States and in affected countries in West Africa to prevent the spread of Ebola.

Exit screening in countries with Ebola outbreaks

Since the beginning of August, CDC has been working with airlines, airports, ministries of health, and other partners to provide technical assistance to countries with Ebola outbreaks. CDC has helped affected countries screen departing travelers from these countries (exit screening). Exit screenings are conducted at airports in these outbreak-affected countries to look for sick travelers or travelers exposed to Ebola and to delay them from boarding an airplane until it is safe for them to travel.

We continue to support and strengthen exit screening in these countries with CDC staff, protocols, and educational materials. What exit screening looks like Exit screening might look a little different in each country but contains the same basic elements.

1. All travelers

• Have their temperature taken
• Answer questions about their health and exposure history
• Are visually assessed for signs of potential illness

2. Travelers with symptoms or possible exposures to Ebola are separated and assessed further.

3. This assessment determines whether they are

• Allowed to travel
• Not allowed to travel on a commercial flight and referred to public health authorities for further evaluation

Entry screening in the United States

Looking for sick travelers at U.S. airports Every day, CDC works closely with partners at U.S. international airports and other ports of entry to look for sick travelers with possible contagious diseases. These measures will be enhanced to detect possible cases of Ebola.Because of the Ebola outbreak, CDC and Customs and Border Protection (CBP) are beginning enhanced entry screening of travelers who have traveled from or through Guinea, Liberia, and Sierra Leone. By doing enhanced entry screening at 5 U.S. airports, we will evaluate over 94% of travelers from the affected countries. Our staff at all airports remain trained and ready to respond to any reports of ill travelers, and our robust public health system is prepared to respond and assist.

What enhanced U.S. entry screening looks like

For each arriving traveler who has been in Guinea, Liberia, or Sierra Leone:

1. CBP will give each traveler health information that includes

• Information about Ebola
• Symptoms to look for and what to do if symptoms develop
• Information for doctors if travelers need to seek medical attention

2. Travelers will undergo screening measures to include:

• Answer questions to determine potential risk
• Have their temperature taken
• Be observed for other symptoms of Ebola

3. If a traveler has a fever or other symptoms or has been exposed to Ebola, CBP will refer to CDC to further evaluate the traveler. CDC will determine whether the traveler

• Can continue to travel
• Is taken to a hospital for evaluation, testing, and treatment
• Is referred to a local health department for further monitoring and support

Entry screening is a part of a layered approach. When used with other public health measures, entry screening can strengthen our efforts to battle this virus. It is important that we act as global citizens, continuing to put our full weight behind response efforts in West Africa and providing support for those traveling here from that region.

###

CDC Statement On Airport Screening Of Arrivals From West Africa

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

 

# 9165

 

Since we’ve discussed the limitations of airport screening many times in the past (see Why Airport Screening Can’t Stop MERS, Ebola or Avian Flu), I won’t rehash all of that information again today.  The take-away from that blog was that while screening won’t prevent the entry of many infected individuals, it can have some value:

 

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.

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 given the extended incubation period of many infectious diseases - don’t expect it to catch all  . . . or even the majority . . . of infected individuals entering this, or any other country.

That said, sometimes doing something – even if it has limited value – is better than doing nothing. And airport screening –particularly when targeted at a relatively small number of travelers coming from a handful of Ebola affected nations – isn’t going to be terribly difficult or disruptive. 

 

Here is a press release, emailed out by the CDC this afternoon, explaining how five major international airports will add additional levels of screening for arrivals from the Ebola affected nations of West Africa.   

 

ENHANCED EBOLA SCREENING TO START AT FIVE U.S. AIRPORTS AND NEW TRACKING PROGRAM FOR ALL PEOPLE ENTERING U.S. FROM EBOLA-AFFECTED COUNTRIES

New layers of screening at airports that receive more than 94% of West African Travelers

The Centers for Disease Control and Prevention (CDC) and the Department of Homeland Security’s Customs & Border Protection (CBP) this week will begin new layers of entry screening at five U.S. airports that receive over 94 percent of travelers from the Ebola-affected nations of Guinea, Liberia, and Sierra Leone. 

New York’s JFK International Airport will begin the new screening on Saturday.  In the 12 months ending July 2014, JFK received nearly half of travelers from the three West African nations. The enhanced entry screening at Washington-Dulles, Newark, Chicago-O’Hare, and Atlanta international airports will be implemented next week.

“We work to continuously increase the safety of Americans,” said CDC Director Tom Frieden, M.D., M.P.H. “We believe these new measures will further protect the health of Americans, understanding that nothing we can do will get us to absolute zero risk until we end the Ebola epidemic in West Africa.”

“CBP personnel will continue to observe all travelers entering the United States for general overt signs of illnesses at all U.S. ports of entry and these expanded screening measures will provide an additional layer of protection to help ensure the risk of Ebola in the United States is minimized,” said Deputy Secretary of Homeland Security Alejandro Mayorkas. “CBP, working closely with CDC, will continue to assess the risk of the spread of Ebola into the United States, and take additional measures, as necessary, to protect the American people.”

CDC is sending additional staff to each of the five airports and the new measures begin with CBP officers reviewing travelers’ passports. After passport review:

• Travelers from Guinea, Liberia, and Sierra Leone will be escorted by CBP to an area of the airport set aside for screening.
• Trained CBP staff will observe them for signs of illness, ask them a series of health and exposure questions and provide health information for Ebola and reminders to monitor themselves for symptoms. Trained medical staff will take their temperature with a non-contact thermometer.
• If the travelers have fever, symptoms or the health questionnaire reveals possible Ebola exposure, they will be evaluated by a CDC quarantine station public health officer. The public health officer will again take a temperature reading and make a public health assessment. Travelers, who after this assessment, are determined to require further evaluation or monitoring will be referred to the appropriate public health authority.
• Travelers from these countries who have neither symptoms/fever nor a known history of exposure will receive health information for self-monitoring, be asked to complete a daily temperature log, and be asked to provide their contact information.

Entry screening is part of a layered process that includes exit screening and standard public health practices such as patient isolation and contact tracing in countries with Ebola outbreaks.  Successful containment of the recent Ebola outbreaks in Nigeria and DRC demonstrate the effectiveness of this approach.

In addition, exit screening measures have been implemented in the affected West African countries, and CDC experts have worked closely with local authorities to implement these measures. Since the beginning of August, CDC has been working with airlines, airports, ministries of health, and other partners to provide technical assistance for the development of exit screening and travel restrictions in countries with Ebola. This includes:

• Assessing the capacity to conduct exit screening at international airports;
• Assisting countries with procuring supplies needed to conduct exit screening;
• Supporting with development of exit screening protocols;
• Developing tools such as posters, screening forms, and job-aids; and
• Training staff on exit screening protocols and appropriate personal protective equipment (PPE)

Today, all outbound passengers are screened for Ebola symptoms in the affected countries. Such primary exit screening involves travelers responding to a travel health questionnaire, being visually assessed for potential illness, and having their body temperature measured.  In the last two months since exit screening began in the three countries, of 36,000 people screened, 77 people were denied boarding a flight because of the health screening process. None of the 77 passengers were infected with Ebola and many were diagnosed as ill with malaria, a disease common in West Africa, transmitted by mosquitoes and not contagious from one person to another.

Exit screening at airports in countries affected by Ebola remains the principle means of keeping travelers from spreading Ebola to other nations.  All three of these nations have asked for, and continue to receive, CDC assistance in strengthening exit screening.

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.

Shakes On A Plane

 

Credit Wikipedia

 

 

# 8614

 

The news yesterday that a second MERS infected Health Care Worker (HCW) flew into the United States from Saudi Arabia is additional proof (as if we needed it) that airlines are a competent vector of infectious diseases, and that oceans and borders offer little protection against the proliferation of emerging viruses.

 

The early (prodromal) presentation of MERS can be mild and non-specific enough (typically fever, chills, malaise) to convince most patients – even HCWs who have recently worked in a MERS hot zone – that what they have is nothing more than a `summer cold’. 

Add in the fact that these early symptoms don’t present until days after exposure – well, short of placing Samuel L. Jackson on every international flight - there’s not much hope (warning: gratuitous movie reference ahead) in eliminating Shakes on a Plane.  

 

Granted, one would hope that in this age of emerging infectious disease, anyone feeling unwell on an airline flight would request - and be provided with - a surgical facemask.  HCWs, particularly those coming from an area where MERS is active, should certainly give extra consideration to the fact that they might be infected.

Hopefully some appropriate signage at airports informing passengers of the symptoms of MERS, and that they should notify the flight crew if they feel unwell, will lead to these sorts of measures.

 

But the reality is, denialism – combined with an overwhelming desire to `get home’ – may induce some people to wait to see if they feel worse before saying anything that might endanger their itinerary.  During the initial outbreak of H1N1, we saw airline passengers taking fever-reducers to beat the airport scanners in order to get home (see Vietnam Discovers Passengers Beating Thermal Scanners).

 

During yesterday’s CDC press conference, CDC Director Tom Frieden addressed the topic of airport screening for possible MERS cases:

 

In terms of the border issues, CDC has quarantine stations at all of the major airports of entry in the U.S.  If someone has symptoms, we are immediately contacted.  If need be, we will go on board the plane.  We do not recommend screening of people coming off. We don't find that to be productive.  First off, many people who may be ill may not be identified as being ill.  And second, many people who will be ill with routine colds and minor conditions would be.  So we've looked at that and not found that to be something we would recommend at this time.

 

A bit of a misnomer, `quarantine stations’  aren’t actually quarantine facilities, but are stations - located at 20 ports of entry and land-border crossings (see map below) - that are staffed by CDC medical and public health officers.

 

Location of US CDC Quarantine Stations

 

The CDC Quarantine Station  FAQ lists their Mandate:

 

Authority and Scope

CDC has the legal authority to detain any person who may have an infectious disease that is specified by Executive Order to be quarantinable. If necessary, CDC can deny ill persons with these diseases entry to the United States. CDC also can have them admitted to a hospital or confined to a home for a certain amount of time to prevent the spread of disease.

Daily Activities

Medical and public health officers at U.S. Quarantine Stations perform these activities:

Response

• Respond to reports of illnesses on airplanes, maritime vessels, and at land-border crossings
• Distribute immunobiologics and investigational drugs
• Plan and prepare for emergency response

Quarantinable Diseases by Executive Order

• Cholera
• Diphtheria
• Infectious tuberculosis
• Plague
• Smallpox
• Yellow fever
• Viral hemorrhagic fevers
• SARS
• New types of flu (influenza) that could cause a pandemic

Migration

• Monitor health and collect any medical information of new immigrants, refugees, asylees, and parolees
• Alert local health departments in the areas where refugees and immigrants resettle about any health issues that need follow up
• Provide travelers with essential health information
• Respond to mass migration emergencies

Inspection

• Inspect animals, animal products, and human remains that pose a potential threat to human health
• Screen cargo and hand-carried items for potential vectors of human infectious diseases

Partnerships

• Build partnerships for disease surveillance and control

 

Although it isn’t what most people want to hear, there is no technological barrier that can effectively keep infected people from traveling internationally.  It is the price we pay for having an increasingly mobile, and interconnected, society.

 

Last month, in MERS: The Limitations Of Airport Screening, we looked at the poor performance of airport screening programs during the H1N1 pandemic, and the scientific consensus that screening programs are unlikely to provide much benefit (see Helen Branswell’s Airport disease screening rarely worthwhile, study suggests).

 

 

The good news – at least as far as we know today – is that MERS shows no signs of being anywhere near as contagious as influenza, and that the risks of contracting it through casual contact with an infected person is thought exceedingly low.  Family members, care givers, those with close, prolonged contact, and HCWs appear to be most at risk.

 

Meaning that simply sharing the same air flight, or standing in queue at the air terminal with someone who is infected, is unlikely to present much risk.

The concern is, that over time MERS may gain transmissibility, making it a greater public health threat.   If that will happen is unknowable, but each human infection gives the virus another opportunity to `figure us out’.

 

But whether the next pandemic threat turns out to be due to MERS, one of the many strains of avian or swine flu (or something completely out of left field), our best defense is for emerging viruses be identified and quashed at the source, before they have the opportunity to board a plane and spread globally.

 

Making investments in global health, research, and human (and animal) surveillance relatively cheap insurance for a world that is increasingly vulnerable to another great pandemic.

 

 

Apparently I’m not the only one with MERS and Travel on the brain this morning, as Dr. Ian Mackay has his own offering called:

 

MERS-CoV on a plane!

"Assessment of the MERS-CoV epidemic situation in the Middle East region."
Reprinted with kind permission of author (Dr Vittoria Colizza, pers comm).Click on image to enlarge.

 

This is perhaps a timely reminder of where cases of MERS-CoV may pop-up if we look at the author's analysis of destinations from major departure airports in the Kingdom of Saudi Arabia, Jordan, Qatar and the United Arab Emirates.

(Continue . . . )

MERS: The Limitations Of Airport Screening

 

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

 

 

# 8548

 

As the graphic above illustrates, airline traffic is a very effective conduit for infectious disease, able to transport someone to nearly anyplace in the world in less than 24 hours.  The world’s airlines carry 2.6 billion passengers each year, on more than 17 million flights.

 

In 2003, we saw the SARS virus hop the Pacific on a flight taken by a 78-year-old woman who fell ill in Toronto after visiting Hong Kong, and before that outbreak was contained, 251 people in Canada had been infected, and 44 died (see SARS And Remembrance).

 

So, whenever a virus threatens to spread globally one of the first visible actions taken by many governments is to impose some sort of airport, seaport, or border screening to prevent those who are infected from entering the country. 

 

Over the weekend we saw a declaration of an emergency in all of Egypt’s ports after a MERS case was detected coming in from Saudi Arabia - and quarantined - at the Cairo Airport last Friday.  Today, we are seeing media reports of two more `suspected cases’ being tested, but it is unknown if they are actually MERS cases.

 

Yesterday Malaysia announced an intensive airport screening program for passengers arriving in Kuala Lumpur  (see Visitors entering Malaysia to be screened for Coronavirus). 

 

While certainly reassuring to the public, and likely to pick up at least some symptomatic carriers of an emerging virus, studies to date indicate the effectiveness of airport screening to be pretty limited.

 

One of the big problems lies in the incubation period, that for many viral infections, allows a long `asymptomatic’ window during which someone can travel before showing symptoms. The incubation period of seasonal influenza runs 1 to 4 days (avg. 2 days), measles 7 to 21 days (avg. 14 days), MERS-CoV up to 15 days. 

 

Plenty of time for someone to pass through airport screening, and travel in-country for several days, before showing any outward symptoms of infection.

While we don’t know if asymptomatic carriers of the MERS virus are infectious, we do know that with influenza it is possible to pass on the virus while not showing signs of illness.  So even those who are infected, but never show signs of illness, may be capable of spreading the virus. 

 

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.

And in 2009, during the initial outbreak of H1N1, we saw airline passengers taking fever-reducers to beat the airport scanners in order to get home (see Vietnam Discovers Passengers Beating Thermal Scanners).

 

All `holes’ in the screening process that would allow infected travelers to enter a country undetected.

 

Between the SARS outbreak of 2003 and the 2009 pandemic, we’ve a number of studies that have looked at just how effective airport screening is in a `real world situation’. 

• 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.
• 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 (which did not employ thermal scanners)  were inadequate to slow the entry of the 2009 pandemic flu into their country, detecting less than 6% of those infected.
• 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.

Last year, Helen Branswell reported on the value of airport screening in an article called:

 

Airport disease screening rarely worthwhile, study suggests

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

TORONTO -- 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.

(Continue . . . )

 

Politically, and in terms of reassuring the public, the screening of passenger arriving at airports and other points of entry probably has some merit.  And it may 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.

 

We simply possess no technological shield that would keep an emerging pandemic virus at bay. 

 

Making it desirable that – whenever possible – outbreaks of emerging viruses are quashed as quickly as possible at the source, before they can board an airplane and spread inexorably around the globe.

 

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.

Taiwan Screening Inbound Arrivals From China

 

Thermal Scanner – Credit Wikipedia

# 6922

 

The announcement yesterday morning of two H5N1 cases in the south-central Chinese province of Guizhou (see China: Two H5N1 Cases Reported In Guiyang) has once again raised alerts over the potential spread of avian flu. 

 

While no additional cases have been reported, we often see increased vigilance across Asia whenever H5N1 makes the news.

 

An example comes today from Taiwan’s Central News Agency (CNA), on their CDC’s order to screen arrivals from China for fever or flu-like illness, and to take and test specimens from travelers showing symptoms.

 

 

CDC: Lu Chuan the avian flu strengthen epidemic prevention

2013/02/11 18:08:00

(Central News Agency reporter Lin Honghan) -

The CDC today said that the Chinese mainland the Guizhou outgoing diagnosed two cases of H5N1 influenza, has asked the airport, port personnel to strengthen passenger fever, to investigate the history of bird contact.

 

Department of Health, Centers for Disease Control press release said that the birds history of exposure to inbound travelers from mainland China have flu-like symptoms, quarantine officers will adopt a specimen for examination, and self-health management 10 days.

 

The CDC called for local Taiwanese businessmen go travelers with the plan, you should pay attention to personal hygiene, strengthen wash their hands, do not touch the birds, to avoid infection; return, such as a fever or flu-like symptoms, consult a doctor immediately should wear a mask.

(Continue  . . . )

 

While the screening of inbound passengers for disease symptoms is quite often the first visible public health response when an emerging pathogen threatens, its track record of preventing disease entry into countries is spotty at best.

 

Last April, in EID Journal: Airport Screening For Pandemic Flu In New Zealand, we saw 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, 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.

 

While 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, for that may slow the spread of the illness and might allow more time to develop and deploy a vaccine.

 

Fortunately, we aren’t at the point with the H5N1 virus that it poses a serious global public health threat.

 

That could change, of course, if the virus evolves into a more human-adapted pathogen.

 

The sobering truth is that vast oceans and extended travel times no longer offer us the kind of protection they once did, and we possess no technological shield that would keep an emerging pandemic virus out.

 

All of which makes the funding and support of international public health initiatives, animal health initiatives, and global disease surveillance increasingly important.

 

No matter where on this globe you happen to live.

EID Journal: Airport Screening For Pandemic Flu In New Zealand

 

 

#6285

 

 

During the opening weeks and months of the 2009 H1N1 pandemic a number of countries worked to identify, and isolate, infected passengers arriving at their International airports in an attempt to prevent or slow the arrival of the pandemic virus to their nation.

 

The reaction is a natural one; to deny entry to highly infectious carriers of pandemic influenza.

 

And for some countries – particularly island nations like New Zealand and Japan, with no shared borders – it seems an attractive option.

 

But is it practical?

 

Prior to the pandemic many experts had expressed doubts - given the multi-day incubation period of influenza, the sensitivity of detection equipment, and the near certainty that some carriers will remain asymptomatic – that attempts to identify the infected based on fever, cough, or other outward signs of illness would prove successful.

 

We’ve a new study published ahead of print in the May edition of the CDC’s EID Journal, that indicates that the mostly passive screening methods used at New Zealand’s airport were inadequate to slow the entry of pandemic flu into their country.

 

 

Screening for Influenza A(H1N1)pdm09, Auckland International Airport, New Zealand

Article Contents

Michael J. Hale, Richard S. Hoskins , and Michael G. Baker

Abstract

Entry screening for influenza A(H1N1)pdm09 at Auckland International Airport, New Zealand, detected 4 cases, which were later confirmed, among 456,518 passengers arriving April 27–June 22, 2009. On the basis of national influenza surveillance data, which suggest that ≈69 infected travelers passed through the airport, sensitivity for screening was only 5.8%.

 

Unlike some other countries in 2009, New Zealand did not employ thermal scanners, looking for arriving passengers or crew with elevated temperatures. 

 

(Thermal Imaging for SARS in 2003)

 

The journal article describes their procedure as:

 

Each unwell passenger and crew member was screened for influenza-like illness by a nurse and assessed by a medical officer if illness met the definition of a suspected case. Those whose illness met the case definition had nasopharyngeal swabs taken, were offered oseltamivir, and were sent home or to a facility for isolation. Reverse transcription PCR (RT-PCR) was used to confirm infection. Screening was escalated on April 29 to include all passengers arriving from other countries and stopped on June 22.

 

After running the numbers, and coming up with a detection rate of less than 6%, the authors concluded that:

 

The influenza A(H1N1)pdm09 screening program at Auckland International Airport had low sensitivity. This form of border screening is therefore unlikely to have substantially delayed spread of the pandemic into New Zealand in 2009.

 

Limitations of influenza screening include the high proportion of asymptomatic infected travelers (5), incubation of infections acquired before or during a flight (3), reliance on self-identification, limitations of case definitions, and limitations of thermal scanning (6). Modeling data have shown that the ability of border screening to delay global pandemic influenza is closely linked to the effectiveness of the screening process or travel restriction used.

 

To delay influenza spread by 1.5 weeks, border restrictions need to reduce imported infections by 90% (7). The entry screening program we describe does not meet these standards.

 

 

As previously mentioned, other countries employed thermal scanners and far more strict interdiction techniques during the summer of 2009, yet their track record was not much better.

 

In June of 2009, just as the pandemic was ramping up, I wrote  Vietnam Discovers Passengers Beating Thermal Scanners,  which looked at a Reuters report that a number of sick passengers flying into Ho Chi Minh City in Vietnam took fever reducers (Aspirin, Tylenol, etc) several hours prior to arrival in order to beat the thermal scanners.

 

In December of 2009, in Travel-Associated H1N1 Influenza in Singapore, I wrote about a NEJM Journal Watch 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.

<SNIP>

One quarter of patients were symptomatic when they boarded flights; 15% developed symptoms during travel. Airport thermal scanners detected only 12% of patients overall and only 40% of those with symptomatic infection on arrival.

 

 

And finally, 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.

 

<SNIP>

The positive predictive value for fever was 1.5% for thermal scanners and 4.1% for tympanic thermometers. For influenza, the positive predictive value for the two techniques was 2.8%. None of the 30 passengers who tested positive for influenza had a tympanic temperature of 37.8°C (100°F) or higher, and only 2 had temperatures of at least 37.5°C (99.5°F). Three were asymptomatic. The group concluded that fever is a poor predictor of influenza, which limits the efficacy of thermal screening at entry points.

Jul 13 ICEID abstracts (See Board 168)

 

 

During the 1918 pandemic, when international travel was far less common, a few nations managed to block entry of the pandemic virus by imposing a strict quarantine of all arriving passengers.

 

The four successful quarantines during the 1918 pandemic were in American Samoa (5 days' quarantine) and Continental Australia, Tasmania, and New Caledonia (all 7 days' quarantine).

 

• The Spanish Flu did not reach American Samoa until 1920, and had apparently weakened, as no deaths were reported.

• Australia's quarantine kept the influenza away until January of 1919, a full 3 mon
• ths after the flu has swept New Zealand with disastrous effects.

• Tasmania kept the flu at bay until August of 1919, and health officials believed they received an milder version, as their mortality rate was one of the lowest in the world.

• By strictly enforcing a 7-day quarantine, New Caledonia managed to avoid introduction of the virus until 1921.

 

Eventually, once the quarantines were lifted, the virus did make it to these isolated regions of the world. 

 

Areas that receive a 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 interdict infected travelers won’t be 100%.

The author’s of today’s  EID study summarize:

 

Border screening might be conducted for reasons other than preventing or delaying an epidemic. It might provide public assurance and confidence that something is being done (14). The communication of health information and advice on how to seek treatment is consistently recommended as a pandemic prevention strategy (12,15) and is usually delivered as part of border screening programs. These benefits need to be balanced against the considerable resources used, opportunity cost (resources used for this activity and thereby unavailable for other activities), uncertain effectiveness, and inconvenience of border screening.

To delay or prevent influenza entry at borders, influenza screening needs to be considerably more effective than the mostly passive program described here.

 

 

Despite scant evidence showing that airport influenza screening would do very much to prevent or slow entry of a pandemic virus into a country, many governments may find it difficult not to at least be seen making the attempt.

 

Which – if nothing else – will provide us with further evidence as to its efficacy (one way or the other) after the next pandemic is finished.