M.I. Asher

International Study of Asthma and Allergies in Childhood (ISAAC): rationale and methods.

The aetiology of asthma and allergic disease remains poorly understood, despite considerable research. The International Study of Asthma and Allergies in Childhood (ISAAC), was founded to maximize the value of epidemiological research into asthma and allergic disease, by establishing a standardized methodology and facilitating international collaboration. Its specific aims are: 1) to describe the prevalence and severity of asthma, rhinitis and eczema in children living in different centres, and to make comparisons within and between countries; 2) to obtain baseline measures for assessment of future trends in the prevalence and severity of these diseases; and 3) to provide a framework for further aetiological research into genetic, lifestyle, environmental, and medical care factors affecting these diseases. The ISAAC design comprises three phases. Phase 1 uses core questionnaires designed to assess the prevalence and severity of asthma and allergic disease in defined populations. Phase 2 will investigate possible aetiological factors, particularly those suggested by the findings of Phase 1. Phase 3 will be a repetition of Phase 1 to assess trends in prevalence.

Diet and asthma, allergic rhinoconjunctivitis and atopic eczema symptom prevalence: an ecological analysis of the International Study of Asthma and Allergies in Childhood (ISAAC) data. ISAAC Phase One Study Group.

Several studies have suggested that the increasing prevalence of symptoms of asthma, rhinitis and eczema, could be associated with dietary factors. In the present paper, a global analysis of prevalence rates of wheeze, allergic rhinoconjunctivitis and atopic eczema was performed in relation to diet, as defined by national food intake data. Analyses were based on the International Study of Asthma and Allergies in Childhood (ISAAC) data for 6-7 and 13-14 yr old children. Symptoms of wheeze, allergic rhinoconjunctivitis and atopic eczema symptom prevalence were regressed against per capita food intake, and adjusted for gross national product to account for economic development. Dietary data were based on 1995 Food and Agriculture Organisation of the United Nations data for 53 of the 56 countries that took part in ISAAC phase I (1994/1995). The 13-14 year age group showed a consistent pattern of decreases in symptoms of wheeze (current and severe), allergic rhinoconjunctivitis and atopic eczema, associated with increased per capita consumption of calories from cereal and rice, protein from cereals and nuts, starch, as well as vegetables and vegetable nutrients. The video questionnaire data for 13-14 yr olds and the ISAAC data for 6-7 yr olds showed similar patterns for these foods. A consistent inverse relationship was seen between prevalence rates of the three conditions and the intake of starch, cereals, and vegetables. If these findings could be generalised, and if the average daily consumption of these foods increased, it is speculated that an important decrease in symptom prevalence may be achieved.

Agreement between written and video questions for comparing asthma symptoms in ISAAC

Phase One of the International Study of Asthma and Allergies in Childhood (ISAAC) has reported the prevalence of asthma, rhinitis and eczema symptoms in children. In 99 centres from 40 countries, a total of just under 317,000 13–14-yr-old children also completed a video questionnaire, showing the symptoms and signs of asthma. This first video sequence has been compared to the ISAAC written question asking about current wheezing to explore variations in agreement and the contribution of each questionnaire to wheezing prevalence between centres, by region and language groups. In general, responses to the video questionnaire gave a lower prevalence than the written questionnaire and responses were closely correlated. The overall proportion of agreement was high, mean 0.89, but unbalanced, with good negative agreement but poor positive agreement. Chance corrected agreement using Cohens kappa coefficient, was generally low, with only 20 centres with kappa >0.4. The contribution of each questionnaire to wheezing prevalence also varied between centres and suggests that written questions about wheezing are variably understood and interpreted by 13–14 yr olds. International comparisons of wheezing and its audiovisual presentation suggest that adolescents interpret a written question about wheezing differently from its audiovisual presentation and that this interpretation shows variation between centres. This relationship and the interpretation of both written and audiovisual presentation of symptoms requires further study in order to better predict asthma.

Recent perspectives on global epidemiology of asthma in childhood

New research in asthma epidemiology in children includes the development of the ISAAC programme, which has shown large variations globally in the prevalence of asthma symptoms. Time trends in the prevalence of asthma symptoms have shown a mixed picture of increases in low prevalence centres, and a plateau or even a decrease in high prevalence centres. A range of environmental factors have been studied and some potentially protective associations have been found, as well as potentially aggravating factors. Atopy has less influence on the prevalence of symptoms of asthma in low and middle income countries. Breast feeding exerts a protective effect only on non-atopic asthma in non-affluent countries. Future research should explore these areas further.

A review of cough in children

Cough is a very common symptom of respiratory disease and reason for parents to seek medical attention. The article presents broad clinical guidelines on the approach to childhood cough and discusses current controversies of the management of cough in children.

International correlations between indicators of prevalence, hospital admissions and mortality for asthma in children

BACKGROUND There are extensive data on the prevalence of childhood asthma world-wide but the relationships between asthma symptom prevalence, mortality and hospital admissions have not been investigated. METHODS The International Study of Asthma and Allergies in Childhood (ISAAC) used a standard questionnaire to measure the 12-month period prevalence of asthma symptoms by parental report in 6-7 year olds in 40 countries, and by self-report in 13-14 year olds in 60 countries. The initial survey was in the mid 1990s (Phase One) and this was repeated in the early 2000s (Phase Three). We correlated the prevalence values of any wheeze and severe wheeze with national data on mortality and hospital admissions for asthma in 5-14 year olds. RESULTS All correlations with prevalence were positive. In 13-14 year olds, the correlations between severe wheeze in Phase One and contemporaneous mortality and hospital admission rates were r = 0.32 (P = 0.047) and r = 0.73 (P = 0.003), respectively. In 6-7 year olds in Phase One, the correlation with severe wheeze and mortality was r = 0.42 (P = 0.024). In 14 countries the correlation between admission and mortality rates in the 5-14 year age group was r = 0.53 (P = 0.054). CONCLUSIONS There are consistently positive associations between asthma symptom prevalence, admissions and mortality. The prevalence of asthma symptoms in children obtained from local questionnaire studies may provide a guide to estimate the incidence of severe episodes of asthma in countries with incomplete data on hospital admissions or mortality, or vice versa.

Changes over time in the relationship between symptoms of asthma, rhinoconjunctivitis and eczema: a global perspective from the International Study of Asthma and Allergies in Childhood (ISAAC).

BACKGROUND The International Study of Asthma and Allergies in Childhood (ISAAC) identified trends in the prevalence of symptoms of asthma, rhinoconjunctivitis and eczema over a seven-year period. We hypothesised that environmental influences on the three diseases are different and therefore investigated the correlation over time between trends in the prevalence of these diseases and their combinations at centre and individual level. METHODS Centre level analyses were correlations between time trends in the prevalence of symptoms. At an individual level, odds ratios were calculated for associations between symptoms between Phases One and Three. We also investigated potential effect modification in the younger versus older age group; male versus female; and by average Gross National Income per capita (GNI). RESULTS Both phases were completed in 66 centres in 37 countries for the 6-7 year age group and in 106 centres in 56 countries for the 13-14 year age group. We found that the correlations in time trends were stronger for the older age group than the younger one. Between symptoms of diseases, correlations of time trends were the strongest for rhinoconjunctivitis with eczema and weakest for eczema with asthma. The relationship between the three diseases was generally consistent over the seven-year period, and there was little association found with average GNI. CONCLUSIONS Despite some increase in the proportion of children with symptoms of asthma, rhinoconjunctivitis and eczema, the pattern between the three diseases has not changed much, suggesting that similar factors may be affecting them at a global level.

The Global Asthma Network rationale and methods for Phase I global surveillance: prevalence, severity, management and risk factors

The Global Asthma Network (GAN), established in 2012, followed the International Study of Asthma and Allergies in Childhood (ISAAC). ISAAC Phase One involved over 700 000 adolescents and children from 156 centres in 56 countries; it found marked worldwide variation in symptom prevalence of asthma, rhinitis and eczema that was not explained by the current understanding of these diseases; ISAAC Phase Three involved over 1 187 496 adolescents and children (237 centres in 98 countries). It found that asthma symptom prevalence was increasing in many locations especially in low- and middle-income countries where severity was also high, and identified several environmental factors that required further investigation. GAN Phase I, described in this article, builds on the ISAAC findings by collecting further information on asthma, rhinitis and eczema prevalence, severity, diagnoses, asthma emergency room visits, hospital admissions, management and use of asthma essential medicines. The subjects will be the same age groups as ISAAC, and their parents. In this first global monitoring of asthma in children and adults since 2003, further evidence will be obtained to understand asthma, management practices and risk factors, leading to further recognition that asthma is an important non-communicable disease and to reduce its global burden. The Global Asthma Network undertakes global studies of asthma surveillance, management and risk factors http://ow.ly/h67s305t9vS

The prevalence of atopic symptoms in children with otitis media with effusion

Objective: To determine the prevalence of allergic symptoms in children with otitis media with effusion (OME). Study Design: A validated questionnaire from the International Study of Asthma and Allergies in Childhood was used to determine the prevalence of allergic symptoms in children. The questionnaire was completed by the parents of children with OME undergoing ventilation tube insertion, and the results were compared with a large reference group of school children of the same age. Subjects and Methods: Children aged 6 or 7 years old with OME confirmed intraoperatively during ventilation tube insertion between 2001 and 2005 (n = 89). The prevalence of allergic symptoms and nasal symptoms in children with OME was compared with an age-matched reference group. Results: There was no difference in the prevalence of allergic symptoms suggesting rhinoconjunctivitis, asthma, or eczema between the OME and reference group. The prevalence of nasal symptoms, however, was greater in the children with OME than in the reference group 38.2 percent versus 23.5 percent (odds ratio = 2.01; 95% confidence interval, 1.30-3.10; P < 0.001). Conclusion: The prevalence of allergic symptoms was similar in 6- to 7-year-old children with OME and the reference group, suggesting a limited effect of allergy in the pathogenesis of OME in this age group. Nasal symptoms were more common in the OME group, which may reflect a higher prevalence of adenoidal hyperplasia.

The challenges of replicating the methodology between Phases I and III of the ISAAC programme.

BACKGROUND The International Study of Asthma and Allergies in Childhood (ISAAC) used standardised methods to examine symptom prevalence of asthma, rhinitis and eczema in adolescents and children between Phases I and III. Centres followed essential rules to ensure comparability of methodology, examined by a centralised data centre. METHODS Centre reports (CRs) were compared for both phases and age groups. Methodological differences were categorised under major deviations (centres excluded), minor deviations (deviations identified in published tables) and very minor deviations (deviations not identified). RESULTS There were 112 CRs for adolescents and 70 for children. Six centres for adolescents and four for children had major deviations and were excluded. Minor deviations (35 for adolescents and 20 for children) were identified in the publications. Very minor deviations (92 for adolescents and 51 for children) were not identified. The odds ratios for having any differences in methodology between phases with a change in Principal Investigator were 0.80 (95%CI 0.36-1.81) for adolescents and 0.91 (95%CI 0.32-2.62) for children. CONCLUSION The majority of the centres replicated the ISAAC methodology to a high standard. Careful documentation of methodology using standardised tools with careful checks allows the full potential of studies such as ISAAC to be realised.