Wednesday, May 30, 2007

XDR-TB

I've been following the story about the XDR-TB patient in forced isolation. I have been wondering where he went after being in Montreal.
The male passenger flew to Paris from his home in Atlanta on May 12 on Air France 385 and arrived in Paris on May 13. He returned to the United States on May 24 after taking Czech Air 104 to Montreal from Prague. The man drove into the United States that day and entered a hospital in New York City on May 25.
I've been wondering about the likelihood of contracting an illness such as this virulent strain of XDR-TB while being on an airplane. I will be traveling to Iceland, Sweden, and Denmark in a few weeks and would like to know if there is a particularly healthy area of an airplane. I have discovered that TB has been contracted on ships with circulating air, but that was over several days and not hours. I have also discovered that sitting in the middle row and in the middle of the airplane is the healthiest part of the plane.

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.

I guess I'll stick to my preference for the aisle seat. :-)




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