Participants

Participants must be 1 to 8 years of age and meet one or more of the following criteria:

The case child has to have had asthmatic symptoms within the last year and in this period no changes in the home arrangements must have been made. It is especially important that the flooring in the child's bedroom is unchanged. The control child has to be healthy which means without any documentation of asthma and allergies.

The asthma diagnosis is based on at least 2 or 3 typical symptoms: expiratory wheezing, dyspnoea or cough. These symptoms must be present also in periods without upper airway infection [10].