We would like to thank D.L. Hahn for his interesting comments on our recent paper in the European Respiratory Journal. No conclusive explanations have been given thus far on the apparent levelling off of asthma prevalence in children. It has been suggested that the underlying cause of the asthma increase in past decades was due to changes towards a westernised lifestyle. However, it is unlikely that the recent observed plateau, or even decrease, would be due to a stabilisation in a westernised lifestyle. The most likely explanation to us seems that a prevalence plateau of all genetically predisposed children has been reached. This means that children who have a genetic predisposition become asthmatic due to relevant exposure. This relevant exposure could indeed be acute primary infections. Moreover, asthmatic children may be diagnosed earlier because of earlier symptom presentation followed by correct diagnosis and therapy. It has previously been shown that underpresentation of asthma symptoms will normally lead to underdiagnosis of asthma, resulting in underestimated asthma prevalence 1. Prior to the 1980s, general practitioners in the Netherlands were reluctant to label asthmatic symptoms in children as having a diagnosis of asthma, since the social consequences and the impact of this diagnosis were far-reaching. Together with the steroid phobia in the general public at that time, this probably resulted in an underdiagnosis of asthma. This changed considerably due to the introduction and subsequent widespread use of inhaled corticosteroids in the following years. It is interesting to note that when we compared two identical surveys in Germany and the Netherlands from 1995 and 1997, in Dutch–German borderland, the asthma diagnosis was more prevalent in Dutch children with recent asthmatic complaints (50–60%), whereas >90% of the German children with recent asthmatic complaints were diagnosed with bronchitis. This resulted in a more frequent use of inhaled steroids and bronchodilators in Dutch children as compared with German children 2.
We cannot exclude the fact that a possible geographically heterogeneous worldwide Chlamydia pneumoniae pandemic could contribute to changes in asthma prevalences in different countries. However, it seems unlikely to us that this would be the sole explanation, as not all asthmatics (established or newly diagnosed) have C. pneumoniae present in bronchoalveolar lavage fluid. Moreover, the widespread use of (macrolide) antibiotics has not prevented a clear increase in asthma prevalence. On the contrary, it seems that a decrease in hospitalisation and mortality is strongly associated with an increase in the use of inhaled steroids 3, and there is no indication that this is associated with the use of antibiotics.
However, it is certainly worthwhile to pay attention to the so-called Chlamydia-asthma theory proposed by D.L. Hahn and to investigate the presence of Chlamydia pneumoniae or other infectious organisms in new asthma patients.
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