International comparative studies, investigating whether disease incidence or prevalence rates differ between populations and, if so, which factors explain the observed differences, have made important contributions to the understanding of disease aetiology in many areas. In Phase I of the International Study of Asthma and Allergies in Childhood (ISAAC), the prevalence rates of symptoms of asthma, allergic rhinitis and atopic eczema in 13–14-yr-olds, assessed by standardised questionnaires, were found to differ >20-fold between the 155 study centres around the world. Phase II of ISAAC aims to identify determinants of these differences by studying informative populations.A detailed study protocol was developed for use in community-based random samples of children aged 9–11 yrs. The study modules include standardised questionnaires with detailed questions on the occurrence and severity of symptoms of asthma, allergic rhinitis and atopic eczema, their clinical management, and a broad range of previous and current exposure conditions. In addition, standardised protocols were applied for examination of flexural dermatitis, skin-prick testing, bronchial challenge with hypertonic saline, blood sampling for immunoglobulin E analyses and genotyping, and dust sampling for assessment of indoor exposures to allergens and endotoxin.To date, ISAAC II field work had been completed or started in 30 study centres in 22 countries.The majority of centres are in countries that participated in International Study of Asthma and Allergies in Childhood Phase I and reflect almost the full range of the observed variability in Phase I prevalence rates.

Pulmonary insufficiency is the main cause of death in cystic fibrosis (CF). We analysed forced expiratory volume in 1 s (FEV₁) data of 14 732 patients registered in the European Cystic Fibrosis Society Patient Registry (ECFSPR) database in 2007. We used linear and logistic regressions to investigate associations between FEV₁% predicted and clinical outcomes.Body mass index (BMI), chronic infection byPseudomonas aeruginosa, pancreatic status and CF-related diabetes (CFRD) showed a statistically significant (all p<0.0001) and clinically relevant effect on FEV₁% pred after adjusting for age. Patients with a lower BMI experience a six-fold increased odds ratio (95% CI 5.0–7.3) of having severe lung disease (FEV₁<40% pred) compared to patients with normal BMI. Being chronically infected withP. aeruginosaincreases the odds ratio of severe lung disease by 2.4 (95% CI 2.0–2.7), and patients with pancreatic insufficiency experience a 2.0-fold increased odds ratio (95% CI 1.6–2.5) of severe lung disease compared to pancreatic sufficient patients. Patients with CFRD have a 1.8-fold increased odds ratio (95% CI 1.6–2.2) compared to patients not affected.These potential risk factors for pulmonary disease in patients with CF are to some degree preventable or treatable. We emphasise the importance of their early identification through frequent routine tests, the implementation of infection control measures, and a timely initiation of relevant therapies.