The relationships between mite and cat allergen levels in the home, skin test reactivity, and severity of asthma were explored in 120 asthmatic subjects, 57 in Vancouver and 63 in Winnipeg. Patients in the two cities were similar in age, gender distribution, and severity of asthma. Skin tests were performed using 13 common allergens, including D. pteronyssinus, D. farinae, and cat dander, as well as control subjects. Patients recorded their asthma symptoms, medication requirement, and twice daily peak expiratory flow rate for 1 yr. Dust samples were collected every 3 mo during each season of 1992 through 1993 in both cities. Mite and cat allergen levels were determined with an ELISA using monoclonal antibodies against Der p I, Der f I, and Fel d I. There was no relationship between skin test reactivity and levels of mite and cat allergens. In children with positive skin tests to either mite allergen, total mite (sum of Der p I and Der f I) allergen level was positively related to the mean daily symptom score and negatively related to the daily mean PEF (% of predicted). There was no such relationship among adult asthmatic patients with positive skin tests to either mite allergen. No relationship was found between cat allergen level and the severity of asthma.
The homes of 120 patients with asthma, 57 in Vancouver and 63 in Winnipeg, were studied. The characteristics of the homes were assessed by a questionnaire. Dust samples were collected and the indoor relative humidity was measured four times during the year covering all four seasons in both cities. Mite allergen levels were determined using monoclonal antibodies against Der p I and Der f I by the ELISA method. The mean levels of both mite allergens in mattress and floor samples in the homes in Vancouver and in Winnipeg were relatively low for all seasons. Mite allergen levels were found to be associated with city, season and individual home differences. They were significantly higher in Vancouver than in Winnipeg. Der p I and Der f I in mattress samples in both cities and Der f I in floor samples in Vancouver, varied by season. The indoor relative humidity level in the homes in Vancouver were also significantly higher than those in Winnipeg. There was, however, no significant association between the levels of indoor relative humidity and the levels of mite allergens after adjusting for variations in city, season and individual home. Although individual home differences were highly associated with mite allergen levels, only a few home characteristics were found to be related to mite allergen levels such as the type and the age of the home, the type of heating, the use of feather pillows and the number of occupants in the homes. Whether low levels of mite allergens are partially responsible for the relatively low prevalence of childhood asthma in Canada remains to be investigated.
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