This is an odd one. A study of 5191 adults showed an
association between air pollution and attacks of acute appendicitis.
Background: The pathogenesis of appendicitis is
unclear. We evaluated whether exposure to air pollution was associated
with an increased incidence of appendicitis.
Methods: We identified 5191 adults who had been
admitted to hospital with appendicitis between Apr. 1, 1999, and Dec.
31, 2006. The air pollutants studied were ozone, nitrogen dioxide,
sulfur dioxide, carbon monoxide, and suspended particulate matter of
less than 10 µ and less than 2.5 µ in diameter. We estimated the odds
of appendicitis relative to short-term increases in concentrations of
selected pollutants, alone and in combination, after controlling for
temperature and relative humidity as well as the effects of age, sex
Results: An increase in the interquartile range of
the 5-day average of ozone was associated with appendicitis (odds ratio
[OR] 1.14, 95% confidence interval [CI] 1.03-1.25). In summer
(July-August), the effects were most pronounced for ozone (OR 1.32, 95%
CI 1.10-1.57), sulfur dioxide (OR 1.30, 95% CI 1.03-1.63), nitrogen
dioxide (OR 1.76, 95% CI 1.20-2.58), carbon monoxide (OR 1.35, 95% CI
1.01-1.80) and particulate matter less than 10 µ in diameter (OR 1.20,
95% CI 1.05-1.38). We observed a significant effect of the air
pollutants in the summer months among men but not among women (e.g., OR
for increase in the 5-day average of nitrogen dioxide 2.05, 95% CI
1.21-3.47, among men and 1.48, 95% CI 0.85-2.59, among women). The
double-pollutant model of exposure to ozone and nitrogen dioxide in the
summer months was associated with attenuation of the effects of ozone
(OR 1.22, 95% CI 1.01-1.48) and nitrogen dioxide (OR 1.48, 95% CI
Interpretation: Our findings suggest that some
cases of appendicitis may be triggered by short-term exposure to air
pollution. If these findings are confirmed, measures to improve air
quality may help to decrease rates of appendicitis.
Obviously, this is a preliminary finding. Additional studies,
including replication, would be needed prior to drawing any
conclusions. So why is it interesting?
The finding is largely counterintuitive, perhaps (depending on how your
intuition works). After all, air pollution does not directly
contact the appendix. It might be tempting to infer that this is yet
another correlation-without-causation study. After all, there
are many such studies that show correlations, that later turn out to be
On the other hand, there
between cardiovascular disease and air pollution. This may be
related to href="http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/6123/report/F">acute
hemodynamic effects (increased blood pressure,
vasoconstriction) as well as href="http://oem.bmj.com/cgi/content/full/64/6/373">inflammation.
It appears that air pollution can cause damage to the lining
of blood vessels, via inflammation. This can lead to blockage
of the blood vessel. Thus, it would stand to reason that a
similar process could take place in the lining of the appendix.
It does not prove it, of course, but what it does show is
that such a mechanism is at least feasible, contrary to the