Indoor factors and asthma in Hamburg and Erfurt as part of the INGA Study: aims and methods

Previous studies clearly revealed that the prevalence of respiratory symptoms, atopic sensitization, and bronchial hyperresponsiveness among adults and children were higher in West Germany compared to East Germany. The aim of the here described part of the joint project INGA (Indoor exposure and Genetics in Asthma) was to assess prospectively the incidence, prevalence, and trends for asthma, bronchial hyperresponsiveness, and atopic diseases over a time period of 10 years (1991-2003) in West and East Germany with special respect to indoor exposure. The study was designed as a case-control study following a cross-sectional study performed from 1990 to 1992 within the European Community Respiratory Health Survey (ECRHS) including 100 cases and 100 controls in each center in Hamburg and Erfurt. Using the identical methods as the ECRHS, the participants were again characterized by a detailed questionnaire, spirometry, methacholine inhalation challenge, skin prick testing, and determination of total and specific immunoglobulin E. Measurements of indoor exposure to allergens, endotoxins, moulds, volatile organic chemicals, and nitrogen dioxide were performed in the apartments of all subjects. The study design of the indoor factors part of INGA is published as a reference for those who wish to know more of the methods used and also to give other groups who wish to collect comparable data access to a detailed methodology.