Associations between multiple indoor environmental factors and clinically confirmed allergic disease in early childhood

Background: Previous studies, mainly questionnaires have reported associations between some indoor environmental factors and allergic diseases. Our aim was to investigate the possible association between objectively assessed indoor environmental factors and clinically confirmed asthma, rhinoconjunctivitis and atopic dermatitis.

Method: A crosssectional case-cohort study (n = 500) based on 2835 children, aged 3–5 years, responding to a questionnaire, consisted of 300 subjects randomly selected and 200 cases with at least two parentally reported doctor diagnosed allergic diseases (asthma, allergic rhinoconjunctivitis or atopic dermatitis).

The same physician conducted a clinical examination of all the 500 children including structured interview on allergic heredity, clinical and medical history. Specific s-IgE against inhalant and food allergens was determined. The homes were investigated by inspectors assessing air change rates, relative humidity, temperature, CO2, and dust samples were collected for analyses of indoor allergens, phthalates, nicotine and polyaromatic hydrocarbons.

The diagnosis of allergic disease was based on internationally accepted criteria. Result: In the base group (n = 300) asthma was clinically diagnosed in 5.1%, rhinoconjunctivitis in 5.1% and atopic dermatitis in 11.0%. Air change rates were below the recommended 0.5 in 56% of all the homes. Air change rates were higher among children asthma/rhinoconjunctivitis (P < 0.05).

Stratified analyses showed lower air change rates (P < 0.05) in sensitized children with asthma. Concentrations of nicotine and house dust mite allergens were higher (P < 0.05) and cat allergens lower (P < 0.05) in the asthma group. When the diagnosis of allergic disease was based solely on questionnaire data no significant associations between environmental factors and allergic disease were found.

Conclusion: Air change rates were insufficient in the majority of the homes, and low rates were associated with higher concentrations of HDM allergens and sensitization in children with asthma. Asthma was associated with higher levels of nicotine and phthalates in dust. Pet keeping history proved an active avoidance behavior against cats.

The lower levels of cat allergens among asthmatics may reflect avoidance behavior agains ‘visible’ allergen sources (cat) but not to ‘invisible’ allergens (HDM). Questionnaire studies are inappropriate for evaluation for analysis of interaction between indoor.