Am. J. Respir. Crit. Care Med.,
Volume 164, Number 7, October 2001, 1109a-1109b
REBUTTAL FROM DRS. PLATTS-MILLS, WOODFOLK
AND SPORIK
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ARTICLE |
We would like to focus on two of the arguments that von Mutius has presented. The first is that because many children
wheeze in early childhood, any effects on prevalence would
have to occur in infancy or even in utero. The second is that
because exposure to farm animals can be protective, the decline in farming could have led to the increase in asthma.
There is no doubt that early wheezing is common and that
many children who subsequently have persistent wheezing,
that is, asthma, have had episodes of some kind in the first 2 years of life. However, the evidence that early wheezing has
increased is less clear. Indeed, in the Mayo Clinic study, the
only evidence of an increase is related to children over 4 years
of age (1). It is important to realize that more than half the
cases of asthma have a later onset and that the disease could
have increased in prevalence because of increased persistence
rather than increased incidence (2, 3). We would argue that
many changes in life style, including diet, immunization, increasing obesity, and the associated decline in physical activity, could all have contributed to the increase in asthma in
childhood. Given the poor evidence of in utero sensitization to
dust mite or other inhalants, and the fact that antibody responses to mite are minimal before age 2 years, it seems unlikely that in utero events can explain the effect (4).
von Mutius and colleagues in Bavaria have elegantly shown
that early contact with farm animals can decrease the risk of
sensitization and asthma. This would seem to be the same phenomenon that Blackley reported in 1873 (5). We suggest that
the real changes in cleanliness in the United States occurred
early in the 20th century. Those changes coincide with the increase in seasonal hay fever. By contrast, the increase in
asthma, particularly in the poorest sections of the American
population, has occurred over a period when it is difficult to
identify any changes comparable to the transition from a rural
to urban existence.
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References |
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Sporik R, Holgate ST, Platts-Mills TAE, Cogswell JJ. Exposure to house-dust mite allergen (Der p I) and the development of asthma in childhood. N Engl J Med 323:502-507.
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Blackley CH. Experimental research in the causes and nature of catarrhus aestivus (hay fever or hay asthma). [Reprinted from Baillière Tindall & Cox, 1873]. London: Dawson; 1959.
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