Farm Exposures and Allergic Disease Among Children Living in a Rural Setting

OBJECTIVES

The purpose of this study was to examine the association between farm exposures and asthma and allergic disease in children while also highlighting the experiences of non-farm rural children.

METHODS

This was a cross-sectional analysis of data collected from across the province of Saskatchewan, Canada in 2014. Surveys were completed by parents of 2275 rural dwelling children (farm and non-farm) aged 0 to 17 years within 46 rural schools. Questionnaires were distributed through schools for parents to complete.

RESULTS

Asthma prevalence was 7.6%, of which 29.5% of cases were allergic. After adjustment for potential confounders, home location (farm vs non-farm) and other farm exposures were not associated with asthma and asthma phenotypes. Those who completed farm safety education were more likely to have asthma (11.7% vs. 6.7%; p = .001) compared to children without asthma. In sub-analyses among 6-12-year-old children, boys were more likely to have asthma (non-allergic) and use short-acting beta-agonists compared to girls. Doing farm work in the summer was associated with an increased risk of asthma [adjusted OR (aOR) = 1.71 (1.02-2.88); p = .041]. Doing routine chores with large animals was associated with an increased risk of asthma [aOR = 1.83 (1.07-3.15); p = .027] and allergic asthma [aOR = 2.37 (95%CI = 1.04-5.40); p = .04].

CONCLUSION

The present study showed that the prevalence of asthma and asthma phenotypes were similar between farm and non-farm rural children. There did not appear to be differential involvement in farming activities between those with and without asthma although those with asthma had more training suggesting possible attempts to mitigate harm from farm exposures.

Indoor mold levels and current asthma among school-aged children in Saskatchewan, Canada

Current knowledge regarding the association between indoor mold exposures and asthma is still limited. The objective of this case-control study was to investigate the relationship between objectively measured indoor mold levels and current asthma among school-aged children. Parents completed a questionnaire survey of health history and home environmental conditions. Asthma cases had a history of doctor-diagnosed asthma or current wheeze without a cold in the past 12 months. Controls were age- and sex-matched to cases. Vacuumed dust samples were collected from the child's indoor play area and mattress. Samples were assessed for mold levels and quantified in colony-forming units (CFU). Sensitization to mold allergens was also determined by skin testing. Being a case was associated with family history of asthma, pet ownership, and mold allergy. Mold levels (CFU/m² ) in the dust samples of children's mattress and play area floors were moderately correlated (r = 0.56; P < 0.05). High mold levels (≥30 000 CFU/m² ) in dust samples from play [adjusted odds ratio (aOR) = 2.6; 95% CI: 1.03-6.43] and mattress (aOR) = 3.0; 95% CI: 1.11-8.00) areas were significantly associated with current asthma. In this study high levels of mold are a risk factor for asthma in children.

Assessment of endotoxin levels in the home and current asthma and wheeze in school-age children

The relationship between household endotoxin and asthma in children is not clear. To further investigate the relationship between sources of endotoxin and childhood asthma, we conducted a case-control study of children with and without asthma and examined their more frequent household exposures in the home. Children ages 6-13 years with current asthma (n = 70) or wheeze only (n = 19) were sex and age matched (+/-1 year) to 107 controls. Play area and mattress dust were collected for endotoxin analysis. Atopic status was determined by skin prick testing for allergies. A family size of >4 per household was associated with higher endotoxin levels (EU/mg) in the bed dust (P < 0.05). Passive smoking (P < 0.05) and the presence of a cat were associated with higher levels of endotoxin in mattress dust. Endotoxin levels in either the play dust or the bed dust did not differ between cases and controls. Within atopic cases, those with higher endotoxin loads (EU/m2) in bed or play areas were more likely to miss school for chest illness (P < 0.05). In this study, household endotoxin is not a risk factor for current asthma overall but may be associated with increased severity in children with atopic asthma.

PRACTICAL IMPLICATIONS

This study did not find that household sources of endotoxin were associated with asthma. However, within atopic asthmatics, asthma severity (as measured by a history of being kept home from school because of a chest illness in the past year) was associated with higher levels of endotoxin in dust from the child's bed. There is a need to further investigate the nature of the relationship between household endotoxin and asthma severity in children which could lead to better management of childhood asthma.

Changing prevalence of obesity in a rural community between 1977 and 2003: a multiple cross-sectional study

OBJECTIVE

To determine the changes in the prevalence of obesity in a rural community between 1977 and 2003.

STUDY DESIGN

A multiple cross-sectional study.

METHODS

The analysis was based on data from four cross-sectional surveys of adults aged 25-59 years, conducted in the town of Humboldt, Saskatchewan in 1977, 1983, 1993 and 2003. People with a body mass index (BMI) > or =30 kg/m(2) were considered to be obese.

RESULTS

Average body weight increased by 8 kg for both men and women during the study period. The increase in BMI was greater in adults aged 25-39 years compared with older age groups. The prevalence of obesity increased from 24% in 1977 to 38% in 2003 for men, and from 16% to 32% for women. The change was more pronounced from 1993 to 2003 than from 1977 to 1993, especially among younger adults. Standardized to the 2003 study population by sex, age and smoking status, the prevalence of obesity was 16.8% in 1977, 22.7% in 1983, 24.7% in 1993 and 34.5% in 2003, and was much higher than the Canadian national average (16% in 2003).

CONCLUSION

There was a dramatic increase in the prevalence of obesity in rural adults, and this was greater in younger adults. Changes in cigarette smoking did not explain the increase. There is an urgent need to identify and implement effective interventions to slow if not reverse the trend, particularly in rural populations.

In vitro production of tumor necrosis factor-alpha by human monocytes stimulated with lipopolysaccharide is positively correlated with increased blood monocytes after exposure to a swine barn

Recently there has been interest in the air quality in and around intensive livestock production facilities, such as modern swine production barns, where agricultural workers and surrounding residents may be exposed to elevated levels of organic dusts. The health effects of these exposures are not completely understood. The study that is reported here is a component of a larger investigation of the relationships among the acute effects of high-concentration endotoxin exposure (swine barn dust), polymorphisms in the TLR4 gene, and respiratory outcomes following exposure to swine confinement buildings. The relationships among a mediator of acute lung inflammation, tumor necrosis factor alpha (TNF-alpha), and clinical responses to acute swine barn exposure were characterized. Analysis of the results showed that in vitro stimulation of human monocytes with as little as 1 ng/ml of lipopolysaccharide (LPS) produced a significant increase in the monocytes that produced TNF-alpha. Although the proportion of TNF-alpha-positive monocytes after in vitro stimulation with 1 ng/ml of LPS was not associated with gender or TLR4 genotype, it was positively associated with the concentration of monocytes in blood after barn exposure. Thus, these two responses to different forms of LPS exposure are significantly correlated, and more responsive monocytes in vitro indicate a forthcoming relative monocytosis, post barn exposure, which may initiate a cascade of chronic inflammation.

Gender, environmental tobacco smoke, and pulmonary function in rural children and adolescents: the Humboldt study

We examined the gender-related association between household exposure to environmental tobacco smoke (ETS) and pulmonary function among 862 children and adolescents aged 6 to 17 years living in the town of Humboldt, Saskatchewan, in 1993. Pulmonary function tests included forced vital capacity (FVC), forced expiratory volume in one second (FEV1), maximum mid-expiratory flow rate (FEF25-75), and flow rates at 75%, 50%, and 25% of vital capacity (Vmax75, Vmax50, and Vmax25). Each pulmonary function test variable was regressed on age, height, weight, and their quadratic and cubic polynomials, with the terms significant at the alpha level of 0.10 being retained. Residuals for the pulmonary function test variables, which are the differences between the observed and predicted values, were calculated. Estimations of ETS exposure were parental smoking status, number of household smokers, total daily cigarette consumption, and number of cigarettes smoked daily at home by household members. Maternal smoking status was significantly related to residual FEF25-75, Vmax75, Vmax50, and Vmax25. Number of household smokers and daily cigarette consumption by household members were significantly associated with FEV1, FEF25-75, Vmax75, Vmax50, and Vmax25, and the association between ETS exposure and pulmonary function was stronger in girls than in boys. Interaction of gender and number of cigarettes smoked daily at home was significantly related to FEF25-75, Vmax75, Vmax50, and Vmax25 among the non-smoking subjects. We concluded that ETS exposure had a larger effect on pulmonary function in girls than in boys.

Effect of age on hospitalized machine-related farm injuries among the Saskatchewan farm population

Machinery-related injuries are the leading cause of fatal and hospitalized injuries on Canadian farms. In Saskatchewan, the proportion of all farm injuries related to farm machinery exceeds that reported for all of Canada. This project examined the relationship between age and various factors associated with farm machine-related injuries in Saskatchewan. A retrospective review of hospital discharge data from the administrative data set of Saskatchewan Health was conducted using external cause of injury codes to identify cases of farm machinery injury that occurred in Saskatchewan during the period April 1, 1990, to March 31, 2000. Log linear estimates of association of various factors in four age groups were derived. There were 1,493 hospitalizations attributed to farm machinery-related injuries. Among the injured cohort, age was a predictor of the rate of injury. Significant association for nature of injury, mechanism of injury, and type of machine varied by age group. These data provide insights for a case-control study of farm machinery-related injuries with the objective of determining personal, environmental, and machine-related factors that are responsible for this serious public health issue.

Segregation analyses of asthma and respiratory allergy: the Humboldt family study

We performed segregation analyses of asthma and respiratory allergy based on data from 309 nuclear families comprising 1,053 individuals living in the town of Humboldt, Saskatchewan, in 1993, using the REGD program of the S.A.G.E. program package. For adults, information on asthma and history of respiratory allergy was provided by the subjects themselves, and for children by their parents. When asthma was considered as the trait in segregation analysis, models of no major effect, with or without familial effects, were rejected, but they were not rejected after adjusting for history of respiratory allergy. The major gene hypothesis was not rejected before adjusting for history of respiratory allergy. When respiratory allergy was analyzed as the trait, both major gene and multifactorial models fitted the data well, regardless of whether there was adjustment for asthma or not. Other covariates adjusted for in the segregation analyses were age, sex, number of household smokers, current smoking, number of household members, generation, and house type. The data suggest that a major gene related to respiratory allergy may explain the familial aggregation of asthma.

Major genetic effects on airway-parenchymal dysanapsis of the lung: the Humboldt family study

We examined familial resemblance and performed segregation analysis for the maximal expiratory flow rate at 50% of vital capacity (Vmax50) and the ratio of Vmax50 to forced vital capacity (FVC), based on data from 309 nuclear families with 1,045 individuals in the town of Humboldt, Saskatchewan, in 1993. Vmax50 is considered as an index of airway function and Vmax50/FVC is considered as an index of airway-parenchymal dysanapsis. Both Vmax50 and Vmax50/FVC were preadjusted for host characteristics (age, height, and weight), environmental factors, and history of respiratory symptoms and diseases in four separate groups (mothers, fathers, daughters, and sons). Both Vmax50 and Vmax50/FVC showed low father-mother correlations and significant parent-offspring and sibling-sibling correlations. Segregation analysis indicated that for residual Vmax50, the model of no-parent-offspring transmission with possible heterogeneity between two generations fitted the data as well as did the general model with arbitrary transmission probabilities. The Mendelian hypothesis for Vmax50 was rejected, which was consistent with our previous findings for other indexes of airway function. For residual Vmax50/FVC, however, a single locus explained all the familial resemblance and both no-parent-offspring-transmission hypotheses [tau(AA) = tau(AB) = tau(BB) = qA and tau(AA) = tau(AB) = tau(BB)] were rejected. The study provides evidence for a single locus influencing airway-parenchymal dysanapsis.

Major genetic effect on forced vital capacity: the Humboldt Family Study

Familial correlation and segregation analyses of forced vital capacity (FVC) were performed on data from 309 nuclear families with 1,045 individuals in the town of Humboldt, Saskatchewan, in 1993. FVC was preadjusted for age, height, and weight in four separate groups (mothers, fathers, daughters, and sons). Residual FVC was standardized within the four groups. Class D regressive model was first used to examine the familial resemblance of FVC without a major gene. While mother-father correlation was not significantly different from zero and mother-sibling and father-sibling correlations were not significantly different from each other, sibling-sibling correlation was greater than parent-sibling correlation. Segregation analysis for all 309 families indicated that both the Mendelian and no-parent-offspring-transmission models fitted the data as did the general model with arbitrary transmission probabilities. Likelihoods under the Mendelian model (LMendelian) and the environmental model (Lenvironmental) were calculated. Based on the value of In(LMendelian/Lenvironmental), 309 families were divided into two groups: 196 families with the value of In(LMendelian/Lenvironmental) greater than zero (group I) and 113 families with the value In(LMendelian/Lenvironmental) less than zero (group II). The Mendelian transmission model without familial correlations was the most parsimonious model for the families in group I. For group II, there were two best models of choice: 1) no-parent-offspring-transmission model with possible heterogeneity plus familial correlations [Akaike's information criterion (AIC) = 1,213.76] and 2) Mendelian transmission plus sibling-sibling correlation model (AIC = 1,202.36). The results suggest there are major genetic mechanisms in FVC with possible heterogeneity.

Association between obesity and high blood pressure: reporting bias related to gender and age

OBJECTIVE

To examine the validity of self-reported information on obesity and high blood pressure (HBP) in relation to gender and age, and to explore the impacts of their misclassification on the association between obesity and HBP.

DESIGN

Community based cross-sectional study.

SUBJECTS

1791 adult subjects living in Humboldt, Saskatchewan, Canada.

MEASUREMENTS

Objectively measured HBP was positive if systolic blood pressure (BP) was > or = 140 mm Hg, diastolic BP was > or = 90 mm Hg or the subject was currently using antihypertensive medication. Self-reported HBP was positive if the subjects gave an affirmative response to the question: 'Has a doctor ever said you had high blood pressure?' Body mass index (BMI) was calculated as weight (kg)/height (m)2. Obesity was defined as a BMI > 27 kg/m2. Measured obesity and reported obesity were based on measured and self-reported information on height and weight, respectively.

RESULTS

The sensitivity of self-reported HBP was low, and was lower for men than for women, and for younger subjects than for older subjects. The specificity was similar for both genders. Obese individuals had higher sensitivity and lower specificity than non-obese individuals. The differential misclassification of self-reported HBP caused a bias away from the null when the relative risk for HBP in relation to obesity was estimated.

CONCLUSIONS

As a result of the gender- and age-related misclassification of self-reported HBP, the modification role of gender and age on the association between obesity and HBP could be altered. The bias caused by self-reported obesity was relatively small and was either toward or away from the null.

Effect of environmental tobacco smoke on cough in children with a history of tonsillectomy or adenoidectomy

We examined the possible impact of tonsillectomy or adenoidectomy (T/A) on the relationship between environmental tobacco smoke (ETS) exposure and respiratory outcomes. This study was conducted in Humboldt, Saskatchewan, in 1993. The target population included all residents aged 6-17 yrs. Of the 1,019 eligible subjects, 892 participated (88%). Estimates of ETS exposure were based on the reported smoking habits of the children's household members. We defined current cough as a positive response to the question: "Does this child usually have a cough?". Information also included morning cough, night cough and a history of T/A. For children with no history of T/A, the prevalence of current cough was 8.9%, 12.2% and 14.5% for those living in families with 0, 1, and 2+ smokers respectively. The corresponding prevalence was 7.0%, 30.2% and 36.8% for children with history of T/A. Similar effects of ETS exposure were observed on morning cough and night cough. The results did not change significantly when we used various ETS measures and controlled for confounding factors. Compared to children living in nonsmoking families and without history of T/A, the adjusted odds ratio for children with a history of T/A was 7.19 (p<0.001) if they were living in families smoking >20 cigarettes x day(-1) at home. The corresponding odds ratio was only 1.64 (p=0.11) for children without a history of T/A. We concluded that children living in smoking family were more likely to cough than those living in nonsmoking families and tonsillectomy or adenoidectomy increased the apparent influence of environmental tobacco exposure on cough.

Evidence for major genetic control of wheeze in relation to history of respiratory allergy: Humboldt family study

We report the results of segregation analyses for wheeze before and after a history of respiratory allergy was taken into consideration. The analyses were based on data from 309 nuclear families with 1,053 individuals living in the town of Humboldt, Saskatchewan in 1993, and were performed by using the REGD program of the SAGE package. For adults, information on wheeze and history of respiratory allergy was provided by themselves, and for children, by their parents. Segregation analyses were first conducted before adjustment for history of respiratory allergy. Other covariates were adjusted including sex, current smoking, household exposure to tobacco smoke, and type of house. A single locus model with residual familial effects fit the data well, but none of the Mendelian models (recessive, dominant, and codominant) could be distinguished. The no-parent-offspring-transmission hypothesis was rejected. However, when the variable of respiratory allergy was included in the models as a covariate, both Mendelian and environmental hypotheses were rejected. The Mendelian model had a relatively lower value of Akaike's Information Criterion than did the environmental model (1095.56 versus 1111.24). The data suggest that a single locus gene explains a portion of wheeze that is related to respiratory allergy, and that common environmental factors and/or polygenes also account for a certain familial aggregation of wheeze.

Influence of environmental tobacco smoke on asthma in nonallergic and allergic children

The relation between exposure to environmental tobacco smoke and childhood asthma is not clear. A 1993 study of 892 subjects age 6-17 years (87.5% of 1,019 eligible subjects) living in Humboldt, Saskatchewan, showed that a lifetime history of asthma and asthma attack during the past 12 months were more common among allergic children than among non-allergic children. The number of household smokers and total daily cigarette consumption by household members were linearly related to both lifetime history of asthma and recent asthma in nonallergic children, but not in allergic children. Out study indicates that allergic status does alter the relation between exposure to environmental tobacco smoke and childhood asthma.

Segregation analysis of two lung function indices in a random sample of young families: the Humboldt Family Study

The Humboldt Family Study was conducted in the town of Humboldt, Saskatchewan, in 1993. Familial correlations and segregation analyses of lung function were carried out in 799 individuals in 214 nuclear families that included 214 fathers, 214 mothers, and 371 children. Forced expiratory volume in 1 second (FEV1) and maximal mid-expiratory flow rate (MMFR) were first regressed on age, height, weight, and their quadratic and cubic terms as well as on smoking status in four groups separately (mothers, fathers, daughters, and sons), with terms significant at the 0.10 level being retained. Residual phenotypes were standardized within the four groups. Class D regressive models were used to perform familial correlations and segregation analyses. For both FEV1 and MMFR, father-mother correlations were not significantly different from zero, and mother-offspring, father-offspring, and sibling-sibling correlations showed no statistically significant difference from each other. Based on the "polygenic" models, the estimated intraclass correlation is 0.132 (+/- 0.035) for FEV1 and 0.171 (+/- 0.039) for MMFR, and the narrow-sense heritability is 0.264 for FEV1 and 0.342 for MMFR. Segregation analysis shows that the "mixed" model with both single locus and polygenic components had a better fit for FEV1 than single-locus or polygenic only models. However, the model which included a nontransmitted environmental factor [tau(AA) = tau(AB) = tau(BB) = qA] and polygenic loci had a better fit than the Mendelian model [tau(AA) = 1, tau(AB) = 1/2, tau(BB) = 0] [Akaike's information criterion (AIC) = 2219.47 vs. AIC = 2222.14]. For MMFR, the Mendelian "mixed" model gave a nonsignificant improvement in loge likelihood compared to the simple polygenic model. Comparison of the single-locus model and Mendelian "mixed" model shows no difference in fitting the data. This study suggests that FEV1 and MMFR are controlled by many loci with no major effects and/or common environmental factors.

Age-related association between body mass index and blood pressure: the Humboldt Study

OBJECTIVE

To investigate how age modifies the relation between body mass and blood pressure.

DESIGN

Community based cross-sectional study.

SUBJECTS

2865 residents aged 6 to 74 years (85.6% of the target population) in the town of Humboldt, Saskatchewan, Canada.

MEASUREMENTS

Body mass index [weight (kg)/height (meters)2], and diastolic and systolic blood pressures.

RESULTS

Among the subjects, 99.6% were of Caucasian origin. With both sexes, there was a stronger relation between body mass index and diastolic blood pressure in younger age groups than older age groups. In males, the increase in mean blood pressure for a 1-unit increase in body mass index (kg/m2) was 0.72, 0.72, 0.41 and 0.47 mm Hg in the 6-14, 15-34, 35-54 and 55-74 year age groups respectively. In females, the correspondent increase was 0.95, 0.57, 0.46 and 0.43 mm Hg. In females, age also modified the relation between body mass index and the prevalence of high blood pressure. The odds ratios for high blood pressure for a 1-unit increase in body mass index in females was 1.33, 1.21, 1.12 and 1.10 in the 6-14, 15-34, 35-54 and 55-74 year age groups.

CONCLUSION

Age significantly modifies the relations of body mass index with mean diastolic blood pressure in both sexes, and with the prevalence of high blood pressure in females. The relations are stronger in children and young adults than in older persons.