Public health officials assert that stronger health screening at airports could hinder the spread of viral outbreaks.

During the early stages of a flu outbreak, such as with the current H7N9 influenza epidemic in China, containment is often the first priority. This is especially true in the age of global air travel, where dangerous germs can cross borders in just a few hours. Excessive travel restrictions, however, would spawn lengthy delays and could paralyze certain sectors of the international airline industry, which generates over half a trillion dollars a year.

Recognizing a possible standoff between commerce and public well-being, the World Health Orgainzation (WHO) revised its international health regulations in 2005 to tackle this emerging dilemma. The new policy aimed "to prevent, protect against, control and provide a public health response to the international spread of disease" while avoiding unnecessary interference with international traffic and trade.

However, the impact of stricter border measures on global travel, in the context of a pandemic, remains unclear.

In a retrospective analysis of the 2009 global outbreak of 'swine flu', epidemiologists propose a strategy that could have stymied the rapid spread of the disease -- in 2 short months, swine flu or 'H1N1 influenza' spread to 170 countries and killed over 1.5 million people.

In this hypothetical scenario, checking all travelers with a direct or connecting flight from Mexico "would be highly disruptive, inefficient and impractical," according to the study, which was led by Dr. Kamran Khan of St. Michael's Hospital in Toronto.

Dr. Khan and her colleagues argue that surveillance efforts should focus on catching people who are departing from areas with high rates of disease -- 'exit screening' -- rather than screening them at their destinations - 'entry screening'.

Up to 90% travelers who had a high risk of spreading the disease from its site of origin, Mexico, could have been identified with this method, while causing the fewest headaches.

"Analysis of the flight itineraries of the 583,774 at-risk travelers who flew out of Mexico in May 2009 revealed that exit screening would have caused the least disruption to international air traffic."

'Entry screening' at the point-of-arrival was just as effective at catching at-risk flyers, but would require surveillance at more airports.

While the best option in this case study, exit screening also comes with "significant political, legal, and practical obstacles", as it places an extra burden on the nation facing the outbreak - 'protect the world from this disease!' --, while it grapples with the financial and social stress of a public health crisis.

"These realities should create incentives for countries that are currently unaffected the epidemic - particularly those with strong travel ties to the affected country - to offer international assistance as a means to protect their own vital interests," say the authors.