Thursday, November 24, 2005

Public health Maginot Line

A lot of people traveling by air this Thanksgiving weekend. We keep hearing the airlines are the front lines of defense against bird flu. This is nonsense.

Two things are true. (1) The airline industry will be severely affected. (2) Bird flu will plausibly arrive via airplanes, probably many of them. There isn't a lot we can do about either except plan for the consequences.

Everyone knows world tourism would be seriously affected if there were an influenza pandemic. SARS was a powderpuff in comparison and it took a real bite out of air travel. Airlines already operate on razor thin profit margins, with half of US airlines in bankruptcy proceedings already. A pandemic could be the coup de grace for some of them. But I'm not an expert on airline economics, so I'll leave it at that.

Public health is another matter. Almost every public health scientist who has thought about it believes quarantine won't work for influenza because it becomes infectious at a stage when people show little or no symptoms. Thus you can't stop it and it is futile to put a lot of resources into trying. Again, the task is to manage the consequences. However sharpening disease surveillance in general, including at airports, may be useful for other diseases. The inability to trace passengers after they leave the plane has been identified as a serious gap in the US disease surveillance and early warning system. CDC is about to propose new rules to require airlines to keep passenger manifests for 60 days and to provide contact information (full proposal and instructions for public comment here). Allegedly there will be strict privacy controls, although we know the government feels no compunction about violating the law when it feels like it. Thus from the public welfare side, these new rules are a balancing act and the balance depends upon how trustworthy the government is. The current one isn't at all trustworthy. One can hope the next one will be an improvement, or at least enough of an improvement to make the balance a net positive. In any event, these new rules will almost certainly be instituted.

In addition the Public Health Service is setting up new "quarantine stations" in international airports. A quarantine station can be as little as a public health service officer in residence or a more elaborate evaluation facility with beds and some equipment. Many "stations" are just desks or offices at the moment. The number has increased from 8 two years ago to 18 today, with a planned expansion to 25 in the near future.

The Northwest Airlines Professional Flight Attendants Association also wants laws requiring continuous ventilation on airplanes. Most airliners have High Efficiency Particulate Air (HEPA) filters that clean recirculated air in the cabin (which mainly moves side to side rather than along the length of the airplane), but not all older regional jets have them. It is estimated that about 15% of planes don't have HEPA filters, which are not required by the FAA. Moreover the systems need to be on all the time, including while sitting on the tarmac in a hold. There is at least one paper in the literature of an influenza outbreak when the airplane ventilation system was inoperative during a ground hold of three hours (Am J Epidemiol. 1979 Jul;110(1):1-6.). Thus increased attention to cabin air quality is a reasonable request.

But neither HEPA filters nor quarantine stations are going to keep out bird flu if the virus becomes as transmissible as the usual human-adapted influenza virus. Airport quarantine measures are a public health Maginot Line.