Effective screening of airline passengers arriving from areas of infectious disease outbreaks

it would have required screening at eighty-two international airports in twenty-six countries.

“One never waits for a fire to spread before putting it out,” said Dr. Khan. “It only makes sense to intervene as early as possible right at the source. The same principle applies to infectious disease outbreaks. To prevent or slow the spread of infectious disease, the most efficient strategy is to control an outbreak at it source, and if this cannot be achieved, to consider screening travelers as they depart the affected area for destinations around the globe.”

The researchers came up with a simple tool any city could use to make a timely, reliable decision about traveler screening during a future outbreak, regardless of where or when the outbreak might occur. Decisions from the tool are based on just three factors: (i) whether effective exit screening at the source of the outbreak is taking place, (ii) whether a city receives direct flights from the source of the outbreak, and (iii) the incubation period of the disease.

“If countries adopt this tool, it would help distinguish settings where traveler screening is reasonable from those where screening is clearly not warranted,” Dr. Khan said. “Taking a highly targeted approach to screening would efficiently produce public health returns while minimizing disruption to international travel, and consequently the world’s economy.”

Dr. Khan noted that screening people as they leave the site of an outbreak does place an additional burden on that country, especially if it’s a resource-poor country, and that it would be in other countries’ interest to provide resources to assist.

“While entry screening may offer the perception of being more closely aligned with the self-interests of a country, the reality is that it’s far more resource intensive and inefficient than exit screening in the source country,” Dr. Khan said. “Since entry-screening consumes valuable health and human resources that could be used more effectively elsewhere, it can actually be counterproductive from both a public health and an economic perspective.”

The reason entry screening is inefficient is that many travelers leaving the source of an outbreak may mingle with other travelers who have no connection to the outbreak. In the case of the H1N1 pandemic, screening all international travelers as they arrived in airports around the world would have been exceedingly inefficient: 116 travelers would have had to been screened for every traveler who may have been exposed to H1N1, or 67.3 million travelers at 1,111 international airports. Dr. Khan said that 90 percent of international trips by air last less than twelve hours, meaning it is unlikely that travelers incubating an infection will board a plane with no symptoms and develop the illness during the trip. The average incubation period for H1N1, for example, is about two days, but 78 and 91 percent of at-risk travelers who flew out of Mexico in May 2009 finished their air travel within six and 12 hours respectively. Even the longest direct flights — seventeen hours to Tokyo and twenty hours to Shanghai — would have taken less than one day.

Each year, more than 700 airlines transport more than 2.5 billion travelers between 4,000 airports. The chief of aviation medicine of the International Civil Aviation Organization said Dr. Khan’s paper “will be very helpful as we continue to determine how to utilize resources to best protect the health of travelers and populations, while minimizing travel disruptions.”

“Countries receiving travelers need to be confident that exit screening has been undertaken efficiently and it’s a great help if communication channels have been established in advance of a public health event. ICAO, the WHO and others have been working together since 2006 to provide just this type of multi-sector/multi-stakeholder network through the Collaborative Arrangement for the Prevention and Management of Public Health Events in Civil Aviation,” said Dr. Tony Evans.

The release notes that the paper does not recommend how passengers should be screened. Some airports, such as those in Hong Kong and Tokyo, routinely use thermal scanners to look for fever among all arriving travelers. In others, traveler questionnaires and direct visualization of travelers for signs of illness are used.

The views expressed by writers in the Bulletin do not necessarily represent the views of WHO.

Funding for the study was provided by the Canadian Institutes of Health Research.

— Read more in Kamran Khan et al., “Entry and exit screening of airline travelers during the A(H1N1) 2009 pandemic: a retrospective evaluation,” Bulletin of the World Health Organization 91, no. 5 (May 2013): 313-88 (doi: http://dx.doi.org/10.2471/BLT.12.114777)