Effects of Airline Travel on Disease Networks
On Tuesday, on an Emirates flight from Dubai to New York, 10 passengers were found to have been infected with common viruses according to the Wall Street Journal (https://www.wsj.com/articles/sick-emirates-passengers-test-positive-for-common-viruses-1536269188?mod=hp_major_pos5&mod=djemHL_t). “Emerging infections” are not uncommon coming from that part of the world, so this large number of passengers becoming ill raised definitive concern about how these viruses might be contained, and if there might have been some infections that those who were ill had contracted and that were unrecognizable or not able to be detected. In fact, many of the ill passengers had just recently been interacting with folks from all over the world as they had potentially been participating in the Hajj pilgrimage, given that they were coming from Mecca.
The reason this event was cause for so much concern is because of networks. When one person (A) has an infectious disease, every person in A’s ego network is at risk for developing that disease, which means if anyone in A’s ego network gets the disease, everyone in that person’s ego network is also at risk, and so on. Assuming that the global friendship network is just one connected component, theoretically everyone in the world would be at risk of contracting this disease. Now, if ten people get that disease, imagine how much faster it could travel, especially if those ten people might have given it to people on the pilgrimage with them who were coming from all over the world and, if that was the case, would presumably have endangered vastly different groups of people than the people heading to New York. Now, imagine if there were MULTIPLE diseases in play.
Luckily for people not on the airplane in question, the infected people were confined at the time they reported feeling ill and so, originally (if we neglect the people back in Dubai who might have been infected without knowing yet), the disease network was limited to the roughly 550 people who were on the flight. However, the ties (edges) between these people (nodes) in this disease network were much stronger than they might have been out in the open because they were all in close proximity and breathing the same air for several hours. So in the 14 hours that these passengers were all on the flight together, all 550 were very likely to get infected even though it was only 550 people. In fact, over 100 people reported symptoms, but thankfully only 10 were tested positive. This effective quarantine allowed the CDC to officially quarantine the passengers after the flight, to further diagnose the nature and scope of the issue and hopefully prevent it from spreading any further.