Global trends in air travel: implications for connectivity and resilience to infectious disease threats

Tuite, Ashleigh R; Bhatia, Deepit; Moineddin, Rahim; Bogoch, Isaac; Watts, Alexander G; Khan, Kamran

Background: Increased connectivity via air travel can facilitate the geographic spread of infectious diseases. The number of travelers alone does not explain risk; passenger origin and destination will also influence risk of disease introduction and spread. We described trends in international air passenger numbers and connectivity between countries with different capacities to detect and respond to infectious disease threats. Methods: We used the Fragile States Index (FSI) as an annual measure of country-level resilience and capacity to respond to infectious disease events. Countries are categorized as: Sustainable, Stable, Warning, or Alert, in order of increasing fragility. We included data for 177 sovereign states for the years 2007 to 2016. Annual inbound and outbound international air passengers for each country were obtained for the same time period. We examined trends in FSI score, trends in worldwide air travel, and the association between a state's FSI score and air travel. Results: Among countries included in the FSI rankings, the total number of passengers increased from 0.791 billion to 1.28 billion between 2007 and 2016. Increasing fragility was associated with a decrease in travel volumes, with a 2.9% (95% CI: 2.3-3.5%) reduction in passengers per 1-unit increase in FSI score. Overall, travel between countries of different FSI categories either increased or remained stable. The greatest increase was observed for travel to Warning countries from Warning countries, with an annual increase of 8,967,623 passengers (95%CI: 6,546,494 to 11,388,753) over the study period. Conclusions: The world's connectivity via air travel has increased dramatically over the past decade. There has been notable growth in travel from Warning and Stable countries, which comprise more than three-quarters of international air travel passengers. These countries may have suboptimal capacity to detect and respond to infectious disease threats that emerge within their borders.