REVIEW ARTICLE Allergic airway diseases in childhood – marching from epidemiology to novel concepts of prevention Laura Hatzler 1 , Stephanie Hofmaier 1 & Nikolaos G. Papadopoulos 2 1 Department of Paediatric Pneumology and Immunology, Charite ´ University Medical Centre, Berlin, Germany; 2 Allergy Department, 2nd Pediatric Clinic, University of Athens, Athens, Greece To cite this article: Hatzler L, Hofmaier S, Papadopoulos NG. Allergic airway diseases in childhood – marching from epidemiology to novel concepts of prevention. Pediatr Allergy Immunol 2012: 23: 616–622. Keywords asthma; allergic rhinitis; epidemiology; hygiene hypothesis; infections; nutrition; environmental risk factors; prevention; allergen avoidance Correspondence Nikolaos G. Papadopoulos, National and Kapodistrian University of Athens, Allergy Research Center, 2nd Pediatric Clinic, 41, Fidippidou, Athens 11527, Greece. Tel.: +30 (210) 7776964 Fax: +30 (210) 7777693 E-mail: ngp@allergy.gr Accepted for publication 4 October 2012 DOI:10.1111/pai.12022 Abstract In the past years, a wide range of epidemiological, clinical, and experimental studies have produced remarkable advances in the field of respiratory allergies in childhood. By the recent investigations on epidemiological trends, risk factors, and prevention of asthma and allergic rhinitis, various exiting concepts have been challenged, and novel innovative approaches have been developed. Pediatric Allergy and Immunology (PAI), with a number of highly relevant contributions between 2010 and 2012, has become an important forum in this area. The prevalence of asthma in some developed countries may have reached a plateau, while in developing countries, where the prevalence was previously low, allergic diseases are still on the increase. A wide array of risk and protective factors, including hygiene, infections, outdoor and indoor air pollution, allergen exposure, breast-feeding practices, nutrition, and obesity, play a multifaceted role in shaping the observed worldwide trends of respiratory allergies. Under the guidance of recent research, prediction and prevention strategies in the clinical practice are progressively changing, the focus moving away from avoidance of allergen exposure and toward tolerance induction. Worldwide trends of asthma and allergies Asthma and allergic rhinitis are particularly prevalent among children (1, 2) in developed countries, and their burden is enormous (3, 4). Studies investigating the epidemiology of allergic diseases have shown a considerable variability in the prevalence of respiratory allergies. According to the phenom- enon of the ‘atopic march’, it is commonly accepted and consistently demonstrated that the occurrence of allergic diseases is strongly related to age (5, 6). A large range of studies have shown higher prevalences not only in developed vs. developing countries, but also within countries between urban compared to rural settings (7–9). This variability implicates that the prevalence is affected by the presence or absence of risk and protective factors (10, 11) affecting both asthma and allergic rhinoconjunctivitis (12). On the other hand, a consistent increase of allergic diseases in childhood has been show within countries (13). Interestingly, several recent investigators suggest that the prevalence of asthma in at least some developed countries may have reached a plateau, while in developing countries, where the prevalence was previously low, allergic diseases are still on the increase. This differential trend has been demon- strated by the worldwide International Study of Asthma and Allergies in Childhood (ISAAC) phase III survey (2) and by smaller studies in individual countries such as Italy (14) and Switzerland (15). Similarly, a recent study in over 4000 Maltese adolescents in 1995 and 2002 (16) demonstrated no increasing trends of asthma prevalence but an improvement in asthma control (less wheezing attacks, disturbed nights, and severe exacerbations). The phenomenon of the rising preva- lence of asthma symptoms in developing regions has been also confirmed in a Turkish study investigating allergic symptoms in 1994 and 2004 in over 5000 preschool children (current asthma for rural and urban regions, 5.2% and 5.8% in 1994; 8.6% and 12.1% in 2004, respectively) (17). Other studies investigated the influence of asthma diagnosis and therapy on the prevalence of asthma symptoms. In Sweden, an increase of physician-diagnosed asthma has been observed between 1996 and 2006 (from 5.7% to 7.4%) paralleled by a growing use of inhaled corticosteroids (55% in 1996 and 67% in 2006); this trend probably reflected a better diagnosis and therapy, as suggested by a parallel decrease of severe asthma symptoms (18). 616 Pediatric Allergy and Immunology 23 (2012) 616–622 ª 2012 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd Pediatric Allergy and Immunology