We read the interesting study by Zutavern et al (1), approaching the problem of assessing the relationship between (exposure to) infections and allergic diseases in an original way by using population level data as a proxy for individual exposure. Exposure between the start of pregnancy and the first birthday was defined as a high incidence of acute respiratory infections in that period in the region (as reported by physicians to the surveillance system in the former German Democratic Republic). The study population included children (aged 5-14 years) born between 1977 and 1990 in three different regions in the former German Democratic Republic and was assessed between 1992 and 1999.
We think, however, that the authors have overlooked an important confounder when adjusting the relationship between exposure and allergic disease, i.e. year of assessment. For already some five years after the re-unification in 1990 there was an important increase in the prevalence of hay fever and atopic sensitization (2).
A second point is that they considered the number of siblings (or rather family size as a proxy variable) as a possible confounder, but the number of older siblings would have been more appropriate as the time frame under study was pregnancy and first year of life.
References
1. Zutavern A, von Klot S, Gehring U, Krauss-Etschmann S, Heinrich J: Pre-natal and post-natal exposure to respiratory infection and atopic diseases development: a historical cohort study. Respiratory Research 2006, 7:81.
2. von Mutius E, Weiland SK, Fritzsch C, Duhme H, Keil U: Increasing prevalence of hay fever and atopy among children in Leipzig, East Germany. Lancet 1998;351:862-6.
Roos M.D. Bernsen PhD(1)
Johannes C. van der Wouden PhD(2)
1. United Arab Emirates University
Al Ain
United Arab Emirates
Department of Community Medicine
2. Erasmus MC – University Medical Center Rotterdam
Re: Pre-natal and post-natal exposure to respiratory infection and atopic diseases development: a historical cohort study.
6 July 2006
We read the interesting study by Zutavern et al (1), approaching the problem of assessing the relationship between (exposure to) infections and allergic diseases in an original way by using population level data as a proxy for individual exposure. Exposure between the start of pregnancy and the first birthday was defined as a high incidence of acute respiratory infections in that period in the region (as reported by physicians to the surveillance system in the former German Democratic Republic). The study population included children (aged 5-14 years) born between 1977 and 1990 in three different regions in the former German Democratic Republic and was assessed between 1992 and 1999.
We think, however, that the authors have overlooked an important confounder when adjusting the relationship between exposure and allergic disease, i.e. year of assessment. For already some five years after the re-unification in 1990 there was an important increase in the prevalence of hay fever and atopic sensitization (2).
A second point is that they considered the number of siblings (or rather family size as a proxy variable) as a possible confounder, but the number of older siblings would have been more appropriate as the time frame under study was pregnancy and first year of life.
References
1. Zutavern A, von Klot S, Gehring U, Krauss-Etschmann S, Heinrich J: Pre-natal and post-natal exposure to respiratory infection and atopic diseases development: a historical cohort study. Respiratory Research 2006, 7:81.
2. von Mutius E, Weiland SK, Fritzsch C, Duhme H, Keil U: Increasing prevalence of hay fever and atopy among children in Leipzig, East Germany. Lancet 1998;351:862-6.
Roos M.D. Bernsen PhD(1)
Johannes C. van der Wouden PhD(2)
1. United Arab Emirates University
Al Ain
United Arab Emirates
Department of Community Medicine
2. Erasmus MC – University Medical Center Rotterdam
The Netherlands
Department of General Practice
E-mail: j.vanderwouden@erasmusmc.nl
Competing interests
The authors have no competing interests