Koopman LP, van Strien RT, Kerkhof M, et al. Am J Respir Crit Care Med. 2002;166:307–313
Purpose of the Study.
To look at the effect of using house dust mite impermeable mattress covers on the development of respiratory symptoms, atopic eczema, and mite sensitization in children born to mothers with allergy.
This study is a report from the Prevention and Incidence of Asthma and Mite Allergy (PIAMA) study which has been conducted in a number of European centers. There were a total of 1282 pregnant women who participated. These women were randomized to the intervention study ([IS]; n = 810) or the natural history study ([NHS]; n = 472). The IS group was further divided into active treatment (n = 416) or placebo treatment (n = 394). Active treatment consisted of the use of polyester-cotton allergen impermeable covers for the mattress and pillows of the mother during the third trimester of pregnancy. The infant’s mattresses were also covered. The placebo group was given cotton covers only. Both the parents and the investigators were blinded as to group assignment. Absolutely no intervention occurred in the NHS. This group served as a second control group. Questionnaires were used during pregnancy and when the child was 3 months old, 1 year old, and 2 years old. Questions were asked of allergy symptoms occurring in the children. The respiratory questions were adapted from the International Study of Asthma and Allergies in Childhood (ISSAC). Questions about atopic dermatitis were taken from a standardized tool. A total serum immunoglobulin E (IgE) and IgE specific to house dust mites, cat, dog, and food allergen were determined. Dust samples were taken during the third trimester of pregnancy and at 3 months of life.
There were a few differences between the 3 study groups. Children in the IS group more frequently had a mother who was allergic to house dust mites and there was a tendency to be born in nonwinter months. The active treatment IS had fewer boys. The treatment group also had more pet ownership and tended to be exclusively formula-fed. House dust mite allergen was measured during the third trimester on both the parent’s and the infant’s beds. House dust mite allergens were found on 58% of the children’s mattresses at the 3-month evaluation. In the active treatment group, there was reduction in the amount of house dust mite allergen on the parent’s bed at 3 months. These data were not presented in the study and will be the topic of a subsequent article. The authors did want to mention that there was allergen reduction with the use of the mattress covers. The primary outcome of the study is the effect of house dust mite avoidance on symptoms. There was no statistically significant difference in the prevalence of respiratory symptoms between the 3 groups. There was a statistically significant increase of recurrent wheezing in the first year of life in the treatment group as compared with the placebo group. There was also no difference in the occurrence of atopic dermatitis between the groups. Further evaluation of the data via logistic regression analysis showed that the children in the active treatment group were less likely to develop night cough without a cold in the second year of life compared with children in the placebo group. Unfortunately, those in the NHS were also less likely to develop the same symptoms. There were no other differences found between the groups with the regression analysis. Asthma medications had been prescribed in 6.6% of the children in the active treatment group, in 8.3% of the children in the placebo group, and 7.3% of the children in the natural history group. There was no difference in symptom severity between the groups. Serum IgE and specific IgE was looked at only in the IS groups, and there was no difference in any of these factors at 1 year of age. Of note, specific IgE to house dust mites was found in only 4 children. There were 10 children who had IgE to cat and 8 with IgE to dog. Fourteen percent of the children had a positive specific IgE to at least 1 allergen. The most common allergens were egg and milk. Finally, the relationship between house dust mite allergen exposure and the development of allergic symptoms was looked at. Atopic dermatitis in the first year of life was less prevalent in children who were exposed to house dust mites. Mite exposure was associated with wheezing at least once during the first year of life and a trend was observed for wheezing in the second year of life. All other associations between house dust mite exposure and the development of respiratory symptoms were not significant. There was also no dust mite dose-response relationship to the development of allergy symptoms.
The use of house dust mite allergen impermeable mattress covers led only to a reduction of nighttime cough. The use of these covers made no difference in the occurrence of other allergic symptoms of the respiratory tract or skin.
The literature suggests that sensitization to house dust mites is a strong risk factor for the development of allergic disease. However, this is controversial, and the results of other studies have provided mixed results. This study shows that mite avoidance measures do not make any difference in the prevalence or severity of allergy symptoms at least in the first 2 years of life. Perhaps the reason why there was no difference was the fact that sensitization was not high in the study population during the first 2 years of life. A positive radioallergosorbert test (RAST) to house dust mites was found in only 4 (0.3%) of 1282 children at age 1 year. RAST-determined sensitivity to house dust mites was very rare at this age. Sensitization to aeroallergens takes time to develop. This appears to be a long-term study. I think it will be important to follow these children over time to see if the measures of mite avoidance performed at this early age will make a difference when the children are older.