The Prevention and Incidence of Asthma and Mite Allergy (PIAMA) birth cohort study: Design and first results

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Abstract
The Prevention and Incidence of Asthma and Mite Allergy (PIAMA) birth cohort study was initiated in 1996. Children born to allergic mothers were enrolled in a double‐blind placebo‐controlled trial for evaluating the use of mite‐impermeable mattress and pillow covers. Children born to allergic and non‐allergic mothers were enrolled in a ‘natural history’ study to assess the role of environmental and dietary risk factors for the development of allergic disease in childhood. Recruitment started by distributing a validated screening questionnaire among >10,000 pregnant women during their first visit to a prenatal health clinic. Allergic mothers‐to‐be were invited to participate in the intervention study. Allergic, and a random sample of non‐allergic, mothers‐to‐be were invited to participate in the ‘natural history’ arm of the study. In the intervention study, homes were visited before birth, 3 months after birth, and 12 months after birth for the collection of dust samples from floors and mattresses. In addition, the homes of about one‐third of the children in the ‘natural history’ part of the study were visited for dust collection when the children were 3 months of age. The intervention study started with 855 participants and the ‘natural history’ study with 3,291 participants. Follow‐up at 3 years of age has now been completed with satisfactory compliance (>90%). A medical investigation and home visit at 4 years of age are nearing completion. Preliminary results show that mite‐allergen levels were lower than found in previous Dutch studies, and that the intervention measure had a significant effect on mite‐allergen levels, without important clinical benefits up to age 2 years old. The allergic families lived in homes with fewer ‘triggers’ such as pets, smoking and carpets than the non‐allergic families, regardless of the intervention. The ongoing PIAMA cohort study will probably reveal useful information concerning effects of allergen load and reduction in the setting of a relatively low mite‐allergen exposure, as well as other variables on the development of allergic manifestions and asthma.