Farm Exposures and Prevalence of Atopy and Asthma among School-aged Children in Agricultural Settings
Background: Asthma and atopic diseases are among the most common diseases afflicting children in Canada. The prevalence and impact of disease seems to differ between urban and rural locations but there are still many unknowns as to reasons for these differences. Some studies have shown an inverse association between farm dwelling and asthma, yet this association has not been always consistent Atopic/non-atopic asthma is one of the most common phenotypes considered in asthma classification yet there have been few studies examining the nature of the classification in with rural populations. Some of the inconsistency could result from differences in the exposure-outcome associations between atopic and non-atopic asthma phenotypes. In addition, there is little information as to what extent children with asthma and/or allergies are exposed to specific activities on the farm. Technology to accurately assess exposures is required such as the use of personal sampling techniques to determine levels of exposures including endotoxin, which has been inversely associated with asthma and atopy and occurs in higher levels in rural compared to urban levels. However, there is limited information about the utility and efficacy of environmental dust collection with personal samplers in children. Objectives: The purpose of this dissertation is to examine the association between farm-related environmental factors and asthma and atopic disease in children. My specific objectives are: i) To determine if early life farm-related exposures are associated with atopy development in school-age children; ii) To estimate the prevalence of atopic and non-atopic asthma and identify risk factors for each phenotype among rural dwelling children; iii) To determine the prevalence of atopy and asthma and its associations with specific farm-related activities and exposures for both farm and non-farm school-age children; iv) To determine whether a personal air sampling pack that we develop could be useful in future studies of lung health with regard to adequate dust collection and feasibility. Methods: This thesis approaches the overall topic of environmental exposures in relation to atopy and asthma. First, it includes an updated systematic review to examine the association between early life exposures to a farm and the presence of atopy measured by skin-prick testing or IgE antibody by blood tests in school-age children. Second, it includes a cross-sectional survey analysis of a provincial dataset of rural dwelling children (The Saskatchewan Rural Health Study) to estimate the prevalence of atopic and non-atopic asthma and identify risk factors for each phenotype among rural dwelling children. Along with a questionnaire report of asthma, skin prick testing was used to asses atopy. Third to examine the associations between specific farm exposures and activities and the presence of asthma, atopy, and atopic asthma phenotypes in children we analyzed data from a separate cross-sectional survey dataset from a provincial sampling of rural dwelling children (The Saskatchewan Farm Injury Study). Fourth, the thesis includes the results of a pilot study to test the feasibility of personal exposure monitoring (PEM) to objectively measure environmental exposures in children. Results: Fourteen studies met the inclusion criteria for the systematic review. The results consistently showed that early farm-related exposures can protect children from becoming atopic at school age. However, there was heterogeneity in the assessment of outcomes and exposures of interest. From the Saskatchewan Rural Health Study, asthma prevalence was 14.7% of which 32.1% of cases were atopic. Location of residence (farm vs non-farm) was not associated with having either atopic or non-atopic asthma. Predictors of childhood asthma, regardless of atopic status were early respiratory illness and a family history of asthma. Being overweight and having a dog in the home were associated with an increased risk of nonatopic asthma. Maternal history of smoking increased the risk of atopic asthma. Compared to those with nonatopic asthma, in the past 12 months, children with atopic asthma were more likely to report a sneezy, runny, or blocked nose or have shortness of breath, whereas those with nonatopic asthma were more likely to have parents who missed work. Those with nonatopic asthma had significantly lower forced expiratory volume in 1 second compared to those with atopic asthma. From the Saskatchewan Farm Injury Study, asthma prevalence was 7.6% and atopy presence was 4.7%. Among those with asthma, 29.5% were atopic. Home location (farm vs non-farm) was not associated with asthma or asthma phenotype. Doing routine chores with large animals was associated with an increased risk of asthma [aOR=1.83(1.07-3.15); p=0.027], and atopic asthma [aOR= 2.37 (95%CI=1.04-5.40); p=0.04]. Using the PEM methods, we collected sufficient dust to detect endotoxin and β-(1 → 3)-D-glucan. Some correlations of these measures between personal (PEM) and settled (play area and mattresses) were observed but were not statistically significant. Evidence from our exit survey regarding the PEM wearing suggested that the design of the PEM device with a fanny pack should be modified to maximize convenience and suitability in order to make its use more practical. Conclusions: Early-life farm exposures were found to be associated with a protective effect on objective markers of atopy. Exposures may contribute differentially to atopic and nonatopic asthma and result in differential clinical presentation or burden although not necessarily with farm dwelling. Those who did routine chores with large animals were at an increased risk of having asthma, specifically atopic asthma. The pilot study successfully showed that the PEM is an effective method to collect sufficient dust to detect endotoxin and β-(1 → 3)-D-glucan levels in children, although modifications should be made to it to make it more feasible in studies of children. The results of this thesis suggest that exposure to a rural setting, including farm activities, can impact outcomes related to atopy and asthma. Future work should focus on refinement of data collection methods to help improve accuracy as well as future study of the characteristics of atopic and non-atopic asthma and its associations with environmental exposures is important for etiologic understanding and management decisions.
Farm exposures, children, asthma, atopy, children, agriculture
Doctor of Philosophy (Ph.D.)