Linköping University Medical Dissertations No 564

Childhood asthma and indoor environment

Aina M Warner

Akademisk avhandling som för avläggande av doktorsexamen i medicinsk vetenskap offentligt försvaras i Berzeliussalen, Universitetssjukhuset i Linköping fredagen den 25 september 1998 klockan 09.00

Fakultetsopponent är docent Lennart Nordvall, Uppsala

Abstract

Background:
During the last decades, the prevalence of asthma in childhood has increased in Sweden as well as in the rest of the western world. Some factor or factors in the indoor environment may be responsible for this. Asthma development and the precipitation of asthma symptoms is dependent on sensitivity to inhalation allergens, of which indoor allergens are of special interest because they are not seasonal. Other factors, such as humidity and inorganic compounds may have a direct effect on the development or the symptoms of asthma. This may be due to an enhancing effect on sensitivity.

Aims:
To find relevant indoor factors for asthmatic children with perennial symptoms living in three climatic zones in Sweden. One part of the thesis was a study on the importance of known indoor allergens on the sensitivity and asthmatic symptoms, the other part aimed at finding new potential allergens that may explain the symtomatology.

Patients and methods:
148 children from Helsingborg, Linköping and Umeå, representing three climatic zones in Sweden were enrolled in the project. They answered a questionnaire which recorded their medication and symptoms, computed to an asthma score, their indoor environment, allergic reactions to dust and animal contacts. Skin tests and blood tests were used to assess sensitivity to indoor allergens.

House dust samples from three locations in the house were analysed with ELISA for detection of indoor allergens (Der p 1, Der f 1, Der m 1, Fel d 1, Can f 1, Per a 1), and for microscopic identification and counting of mites and insects.

In 60 homes a thorough environmental investigation was done by specialised engineers, who judged the house structure, measured ventilation efficiency, humidity, volatile organical compounds and particles. Dust was collected for analysis of moulds, bacteria and endotoxin levels.

Results:
Serum IgE antibodies to inhalation allergens were found in 80 % of the children. Animal dander allergens dominated in terms of frequency of sensitivity (62%), followed by pollen (54%) and mites (35%). Sensitivity to mites was dominating only in the south, animal dander allergens dominated in the north. Sensitivity to animal dander, pollen and mites was associated to an elevated asthma score.

Animal dander allergens were found in all homes, even in homes without pets. Occasional visits by pets augmented the allergen levels.

Current level of exposure at home to house dust mites and storage mites was associated with sensitivity, even at low levels, in contrast to animal allergens at home. Mite allergen levels were usually highest in the bedroom samples, but in 115 of the homes the living-room samples had the highest levels in the home. Humid homes had higher mite allergen levels than dry and well ventilated homes. The use of mite allergens as environmental assays of mite may underestimate exposure levels, if all relevant allergens are not included, for example Der m 1.

Other mites as well as insects are potential new allergen sources.

Discussion and conclusion:
The home environment contains . allergens from animal dander as well as mites and insects. Insufficient ventilation and excess humidity offers a milieu that enhances growth of mites, and has an effect on asthmatic symptoms in its own right. The outdoor climate has an influence on the indoor climate in the number and species of mites found, but in homes with high humidity mite allergens may reach very high levels also in regions where mites normally are not found, such as the northern part. Indoor allergens are important for the sensitivity and symptoms of asthmatic children with perennial symptoms.

Department of Health and Environment, Division of Paediatrics
Linköping University Hospital S-58185
Linköping, Sweden

ISSN 0345-0082 ISBN 91-7219-048-5