NAC Manchester Asthma and Allergy Study ((NAC)MAAS): risk factors for asthma and allergic disorders in adults

Background Asthma and atopic disorders are the most common chronic diseases in the developed countries. Knowledge of the risk factors for these disord ers may facilitate the development of preventive strategies aimed at reduci ng prevalence rates. Objectives To investigate the risk factors for asthma and allergic diseases in a large number of adults who are the parents of children in the Nationa l Asthma Campaign Manchester Asthma and Allergy Study. Methods All pregnant women and their partners attending 'Booking' antenatal clinics were invited to take part in the study. Questionnaire data were co llected including the history of asthma and other atopic diseases, pet owne rship and smoking habits, and skin prick tests were performed. The prevalen ce of atopy and the risk factors for asthma and allergic disorders were inv estigated in all subjects who completed the questionnaire and underwent ski n testing. Statistical analysis was carried out using logistic regression. Initially, risk factors were assessed by univariate analysis to see how eac h potential explanatory variable affected the probability of having allergi c disease. Variables were then tested in a forward stepwise multivariate an alysis. Results In 5687 adult subjects there was a very high (48.2%) prevalence of atopy, and 9.7% of subjects had a diagnosis of asthma. In a multivariate re gression analysis sensitization to dust mite, cat, dog and mixed grasses we re all independently associated with asthma. The odds ratios for current as thma increased with the increasing number of positive skin tests (any two a llergens - OR 4.3, 95% CI 3.3-5.5; any three allergens - OR 7.0 95% CI 5.3- 9.3; all four allergens - OR 10.4, 95% CI 7.7-14; P < 0.00001). Dog ownersh ip (OR 1.31, 95% CI 1.10-1.57; P = 0.003) and current smoking (OR 1.36, 95% CI 1.15-1.62; P = 0.0004) were significantly and directly associated with 'asthma ever'. Thirteen per cent of participants reported a history of ecze ma. In the multivariate analysis the strongest independent associate of ecz ema was sensitization to dog (OR 1.37, 95% CI 1.14-1.63, P < 0.0001). Apart from dog, the strength of the association between sensitization to common allergens and eczema appeared to be much lower than in the case of asthma. The prevalence of hay fever was high (20.6%), and in the multivariate analy sis the association between sensitization to pollen and hay fever was extre mely strong (OR 13.6, 95% CI 11.3-16.3; P < 0.0001). Conclusions The results of the current study emphasize the importance of se nsitization to indoor allergens in asthma. However, evidence of a possible direct role of allergen exposure in asthma causation remains unclear.