Thursday, June 28, 2007

Medical "Air quality" in airplane cabins and resistant TB

I have held for a long time an erroneous idea of the risk of disease transmission aboard airplanes.I envisioned the passenger cabin as some sort of 3-d Petri disk crammed full of various viruses and other pathogens.

An excellent article in the July 2007 issue of Mayo Clinic Proceedings corrected my misconceptions. The editorial " Dealing with threat of Drug-resistant Tuberculosis" written by Dr. Priya Sampathkumar is an excellent review of the basics of drug resistant TB and the quality of air in a plane from a medical point of view and can be found free, full text here.
The recent news stories of a person with XDR-TB (extensively drug resistant TB) traveling repeatedly by air from country to country greatly increases the interest level of this article.

He tells us that the recommended rate of air exchanges in a hospital isolation room for TB is 6-12 exchanges per hour. Modern aircraft have 20-30 exchanges per hour.Further,there are high efficiency particular air filters that remove 99.9% of particles that are between 0.1 and 0.3 micra. Mycobacterium is about 0.5 to 1.0 micra. More reassurance comes from the fact that air enters and leaves the cabin at the same seat row so that there is little flow from the front to the back of the plane. Of course, all of this assumes everything is working as it should and as always anything that can work can break down.

Consistent with this description of how the air is handled in planes is the observation that in all instances of transmission of TB on board a commercial airliner occurred to passengers who were seated within 2 rows of the index case.

The scary factor of the Andrew Speaker case was greatly enhanced by the fact he had XDR-TB. Regular-that is drug sensitive TB-is no longer a scary disease. Treatment with first line drugs for six to nine months results in a cure in 95% of patients.MDR-TB is defined as TB being resistant to both INH and Rifampin and treatment with the less effective,often poorly tolerated second line drugs for 18 to 24 months results in cure anywhere from 50% to 70% of the time.

MDR-TB burst on the scene in the early 1990s mainly in patients who were infected with HIV in whom the mortality rate approached 80% and there were reported instances of transmission to health care workers and prison guards.In 2005 there were 95 cases reported in the U.S but according to the National Jewish website 450,000 cases worldwide.

XDR-TB appeared in 2005 in an outbreak in South Africa and is characterized by resistance to INH,Rifampin,a fluroquinolone, and at least one of the three injectable drugs.From 1993 to 2006 in the United states, 49 cases have been reported with 12 deaths and 12 loss to followup.National Jewish has treated a small number of cases and states that their treatment including resectional surgery may result in a 50% cure rate.Until MDR-TB and XDR-TB came on the scene, surgery for TB was largely a history book chapter, not so now.

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