In many people, asthma appears to be an allergic reaction to substances commonly breathed in through the air, such as animal dander, pollen, or dust mite and cockroach waste products. The catch-all name for these substances, allergens, refers to anything that provokes an allergic reaction. Some people have a genetic predisposition to react to certain allergens.

When these people breathe in the allergen, the immune system goes into high gear as if fighting off a harmful parasite. The system produces a molecule called immunoglobulin E (IgE), one of a class of defensive molecules termed antibodies. The IgE antibody is central to the allergic reaction. For example, it causes mast cells, a type of specialized defensive cell, to release chemical " weapons " into the airways. The airways then become inflamed and constricted, leading to coughing, wheezing, and difficulty breathing -- an asthma attack (definition provided by the US National Institute of Allergy and Infectious Diseases).

Need of comparable indicators for asthma monitoring

The objective of the Community action in the field of public health (2003-2008) is to evaluate the impact on asthma prevalence of possible health policy interventions. These interventions should also focus on the reduction of specific asthma risk factors. For this purpose the European Commission supports, on the framework of the Community action in the field of public health, the IMCA (Indicators for Monitoring COPD and asthma in the EU) Project to develop indicators to monitor asthma in the European Union, to describe the prevalence of asthma related symptoms, asthma at tacks, physician diagnosed asthma by age group, gender, socioeconomic status and geographical area and to monitor changes over time on the indicators proposed.

See IMCA II - Indicators for Monitoring COPD and Asthma in the EU
See web site of the IMCA II - Indicators for Monitoring COPD and Asthma in the EU Project

Need of comparable incidence data for asthma

Before the 1990s a large number of epidemiological studies on the prevalence of asthma were carried out. However, no standardized methods were used and its comparability was very difficult. In early 1990s two large studies were set up and standardized the methods for data collection on asthma. The European Community Respiratory Health Survey was the first study to assess geographical variations in the prevalence of asthma and allergy in young adults using the same instruments and definitions. The study was set up in 1993 and was carried out in two stages and included individuals from 20 to 44 years of age. In stage I, subjects were sent the ECRHS screening questionnaire asking about symptoms suggestive of asthma, the use of medication for asthma and the presence of hay fever and nasal allergies. In stage II, a smaller random sample of subjects who had completed the screening questionnaire were invited to at tend for a more detailed interview- led questionnaire, skin prick test (SPT), blood tests for the measurement of total and specific immunoglobulin-E (IgE), spirometry and methacoline challenge.

Another large international study initiated to gain new insights into the aetiology of asthma and allergic disorders in children through standardized comparisons of diverse child populations worldwide was the International Study of Asthma and Allergies in Childhood (ISAAC) . In this study participated 463 801 children aged 13-14 years in 155 collaborating centres in 56 countries. In the Phase I of ISAAC the prevalence of symptoms of asthma, allergic rhino-conjunctivitis and atopic eczema in 6-7 and 13-15 years old were assessed and > 20 fold differences in prevalences between centres were found. The information was collected by a self administered questionnaire. Phase II of ISAAC (in a large number of countries) assessed the prevalence of objective markers of atopic diseases and investigates atopic determinants. In this phase children from 9 to 11 were included. In this study bronchial responsiveness was assessed using inhaled hyperosmolar (4.5%) saline.

In contrast with these two studies, more recently, the AIRE (Asthma Insights & Reality in Europe) study has been carried out using different methodologies for data collection (telephone interviews) and being nationally representative and including patients with current asthma and from all age groups. The population prevalence of current asthma can be estimated based on the total number of people reported in each household and the total number of people with current asthma in those households. A total of 213 158 people were reported living in the 73 880 households screened for the survey. The total population prevalence of current asthma was 2.7% for the seven AIRE countries.

Asthma mortality is low and there is a tendency to decrease in most European countries. Although mortality is low, most asthma deaths result from acute exacerbations and are generally thought to be avoidable. Increases in asthma deaths, especially those persisting over a long period, thus raise concerns about the potential effects of changes in the medical management of asthma in addition to concerns about changes in asthma's underlying prevalence or severity. Death from asthma may thus be viewed as a sentinel health event.

The GA²LEN (Global Allergy and Asthma European Network) it's a research network (funded by the European Commission's 6th Framework Programme for Research) working to create a permanent and durable structure to coordinate research capacity in Europe on Allergy and Asthma issues coordinated by the University of Gent (Belgium). The objective is to establish an internationally competitive network, to enhance the quality and relevance of research, address all aspects of the disease and eventually to decrease the burden of allergy and asthma throughout Europe.