This is very similar to the rants about the rise in asthma rates in the inner city.
It's absolutely clear that the rise in inner city asthma is due to an increase in cockroach doo-doo. People with allergies tend to react very badly to cockroach droppings, and so if you have more cockroaches, you have more asthma. The solution would be more use of insecticides.
Instead we get this left-wing spin about how this is proof that our air is more polluted, even though the air is continuing to get cleaner. Funny how asthma's not increasing in the suburbs even when those suburbs are downwind from pollution sources. That's because air pollution isn't the problem.
I bet you can find a correlation between the numbers of parents who smoke around young children and the rate of athsma among children.
With more and more parents aware of the negative affects of smoking on children, there are fewer parents who smoke around their kids. So athsma drops.
Maybe there is no true link, but there would be a highly probably link between the correlation and the reality.