It was only last week we posted about XDR-TB. Yesterday CDC warned passengers on two international flights — Air France 385, Atlanta to Paris on May 12 and Czech Air 104, Prague to Canada on May 24 — they may have been infected by another passenger who had Extensively Drug Resistant TB (XDR-TB). Reportedly authorities could not reveal which row the male passenger sat in as this would violate medical confidentiality laws (HIPAA). So anyone on the plane could think themselves at risk, although it was probably only those in the same row and several rows front and aft of the passenger who were really at risk. And the cabin crew, of course.
It’s natural to think of an airplane as the ideal place to contract an infectious disease. After all, you are strapped in a seat in a narrow cylinder for hours at a time, next to people from diverse geographic origins, breathing recirculated air. If this isn’t the perfect recipe for spreading an infectious disease, it is hard to think of what might be better. But in fact there is precious little evidence that airplane rides are a lottery ticket for a respiratory infection, as noted in a 2005 Commentary that accompanied Mangili and Gendreau’s
It turns out that while an airplane provides the smallest volume of air per person of any public space, the movement of air is transverse, i.e., from side to side, not along the length of the airplane. The air descends from the top of the cabin to the middle, sweeping in two circles on either side. Thus the people in the middle section of a wide body jet get the freshest air, with passengers seated to either side getting the air sweeping past the more medial seat mates. The poor soul on the window gets the air from everyone else in the row on their side of the plane (see figure 1 in Mangili and Gendreau). So the seat of the index case is probably critical, although this pattern is “on average.” There is enough turbulence in cabin air to allow currents to go several rows front and aft. While it is true about 50% of the cabin air is recirculated, in all but the smallest regional jets it is passed through HEPA filters first. This was certainly true for the transatlantic planes in the current case.
There are a number of reports in the literature of infectious diseases contracted via airplane travel, including measles, influenza, TB and SARS. But not many. In general secondary cases were within a few rows of the index case, but in one notable instance, Air China flight 112 in 2003, SARS cases occurred in passengers seven rows in front and five rows behind the index case.
The paucity of cases in the literature might mean passenger to passenger transmission happens rarely, or it might merely be a reflection of the difficulty of detecting a disease cluster when all the contacts disperse widely upon reaching their destination. Since TB is largely a large droplet transmission, the belief that transmission is limited to those two rows in front and behind is probably justified.
Probably. But meanwhile the passengers have to be found, evaluated for infection and their contacts, likewise. Welcome to My World. Or should I say, Welcome to Our World. Because we are surely in it together.
Update: Later posts here.