Clinical and Experimental Allergy, 1989, Volume 19, pages 419-424 The relative risks of sensitivity to grass pollen, house dust mite and cat dander in the development of childhood asthma M. R. SEARS, G. P. HERBISONf, M. D. HOLDAWAY*, C. J. HEWITT* ERIN M. FLANNERY and P. A. SILVA* Departments of Medicine, *Paediatrics and Child Health, and ^Preventive and Social Medicine, University ofOtago Medical School, Dunedin, New Zealand Summary The associations between skin sensitivity to various common allergens and the development of childhood asthma were ascertained in a longitudinal study of a birth cohort of New Zealand children up to the age of 13 years. Of 714 children skin-tested, 45-8% were sensitive to at least one of 11 allergens, the most common responses being to rye grass pollen (32-5%), house dust mite (30-1%) and cat dander (13 3%). Allergen- specific relative risk analysis, controlled for the effect of sensitivity to other allergens, demonstrated that sensitivity to house dust mite and to cat dander were highly significant independent risk factors associated with the development of asthma (whether defined as recurrent typical respiratory symptoms, increased airway responsiveness, or the concurrent presence of both), whereas grass sensitivity was not a significant independent risk factor for asthma. Clinical and Experimental Allergy, Vol 19, pp. 419-424. Submitted 27 September 1988; revised 5 January 1989; accepted 11 January 1989. Introduction Childhood asthma is a common problem in New Zea- land [1] and in many other countries [2,3]. Recent epi- demiological studies have reported cumulative prevalence rates of recurrent wheezing of up to 30% in children aged 9 years [1,4]. Atopy is a well known associated feature [5], and was an invariable finding in New Zealand children whose asthma symptoms and increased airway responsive- ness persisted into adolescence [6]. Platts-Mills et al. [7] have suggested that atopy, and especially sensitivity to the house dust mite, may induce and perpetuate airway hyperresponsiveness. We wished to determine the associa- tions between sensitivity to the house dust mite and other common aero-allergens, and the development of child- hood asthma and airway hyperresponsiveness in New Zealand. Subjects and methods We have previously described a birth cohort of children who have been followed biennially from 3 to 13 years Correspondence: Prof. M. R. Sears, Department of Medicine, Univer- sity of Otago Medical School, PO Box 913, Dunedin, New Zealand. [1,8,9]. In brief, 1661 children whose mothers were resident in Dunedin were born in the city maternity hospital between 1 April 1972 and 31 March 1973. Those resident in Otago province at the age of 3 were invited to participate in a multidisciplinary longitudinal health and development study; 1037 (91 %) of 1139 eligible children were enrolled, and by the age of 13,737 were still available for review at the research centre. There were no significant differences in perinatal history between the 1037 enrolled in the study and the full birth cohort of 1661, nor any systematic social, developmental or medical bias evident in the sample of 737 remaining in the study after 10 years compared with the cohort of 1037. Health questionnaires were administered to the parents of the children every 2 years from age 3 up to the age of 11, and to the child at 11 and 13 years. A child was recorded as having asthma if a physician- administered questionnaire to the parent or child yielded a history of recurrent wheezing episodes, whether asso- ciated with exercise, allergen exposure, upper respiratory tract infection or occurring spontaneously, regardless of whether or not the diagnosis of asthma was reported by the parent [1]. The presence or absence of airway 419