My post on the lack of correlation between air pollution (in the form of ozone and particulates) and asthma has led several people to ask me -- well, what else could possibly be causing the rise in asthma cases?
One "cause" for increases in measured disease rates that almost always plays a role in modern epidemiology is better diagnosis and reporting. There have been a number of diseases where changes in definitions and better diagnosis have led to an increase in reported cases, while the actual occurance rate has remained constant. The rise in asthma cases seems to go beyond this effect.
The best guess I have for the increase in
asthma in this country, and the strong positive correlation between
asthma and economic development, is that it has something to do with
indoor pollution. The spike in asthma cases seems to parallel the rise
in energy prices. Beginning in the 1970's, we began sealing up houses
tighter and tighter to conserve energy. Increasing penetration of air
conditioning simultaneously caused people to close the windows. The spread of office-type service work had brought more people indoors. I am
convinced its something inside, not outside, that is causing the asthma spike.
Update: More on the lack of correlation between air pollution and asthma here, this time in California.