Geographical variations in the prevalence of atopic sensitization in six study sites across Canada.

BACKGROUND: Geographical variations in atopic sensitization in Canada have not been described previously. This study used the standardized protocol of the European Community Respiratory Health Survey-1 (ECRHS-1) to investigate the distribution and predictors of atopic sensitization in six sites across Canada and to compare the results with some ECRHS-1 centers. METHODS: Adults aged 20-44 years in six study sites across Canada underwent allergy skin testing using 14 allergens (Dermatophagoides pteronyssinus, Dermatophagoides farinae) cat, cockroach, grasses (Timothy grass, Kentucky grass), molds (Cladosporium herbarium, Alternaria alternata, Aspergillus fumigatus, Penicillium), trees (tree mix, birch, Olea europea), and common ragweed. RESULTS: The overall prevalence of atopy (skin test over 0 mm to any allergen) was 62.7%. There was significant geographical variation in the prevalence of atopy in the six study sites (lowest 55.6% [95% C.I.51.3-59.9] in Prince Edward Island, highest 66.0 [61.7-70.3] in Montreal) and of sensitization to each of the allergens tested even after adjustment for confounders. When the first eight of the nine allergens in the ECRHS were used to estimate the prevalence of atopic sensitization, the prevalence of atopy in Canada was 57% compared with 35.2% overall for centers in the ECRHS. The prevalence of atopy in Vancouver (57% [52.3-61.8]) was close to that of Portland, Oregon (52.1% [46.2-58.0]). CONCLUSION: There was a significant variation in atopic sensitization among different study sites across Canada. The prevalence of atopic sensitization is relatively high in Canada compared with sites in the ECRHS and this may, in part, account for the high prevalence of asthma and asthma symptoms in Canada.

Asbestos-related diseases of the lungs and pleura: uses, trends and management over the last century.

Asbestos is a descriptive term for a group of naturally occurring minerals known to mankind since ancient times. The main types of asbestos (chrysotile, and the amphiboles crocidolite and amosite) differ in chemical structure, biopersistence in human tissue and toxicity. Commercial exploitation, with little thought for environmental controls, increased over the twentieth century, particularly after World War II, to accommodate globalisation and the demands of the world's burgeoning cities. As its ill-health effects, both non-malignant (fibrosis of the lungs or asbestosis; pleural effusion, plaques and thickening) and malignant (mesothelioma, lung and other cancers), became evident, public pressure rose to control its use. The last decades of the last century saw decreases in exposure and rates of asbestosis in industrialised and in some less-industrialised countries, where pleural plaques and malignant mesothelioma are currently the most frequent manifestations of asbestos exposure. Longer follow-up of asbestos-exposed cohorts in mining and manufacturing has also strengthened the evidence of a fibre gradient in toxicity, with chrysotile exhibiting lower toxicity than the amphiboles, and amosite lower toxicity than crocidolite. The last decades of the twentieth century saw stabilisation and/or declines in mesothelioma rates in several industrialised countries. In less-industrialised countries, data on disease are sparse, exposure generally high and rates may peak in the future. Management of asbestos-related disease in the workplace requires collaboration between workers and unions (responsible for monitoring workplace dust levels, to which they must have access) and companies (responsible for engineering controls), reinforced by appropriate government regulations and by community support.

Non-malignant consequences of decreasing asbestos exposure in the Brazil chrysotile mines and mills.

AIMS: To investigate the consequences of improvement in the workplace environment over six decades (1940-96) in asbestos miners and millers from a developing country (Brazil). METHODS: A total of 3634 Brazilian workers with at least one year of exposure completed a respiratory symptoms questionnaire, chest radiography, and a spirometric evaluation. The study population was separated into three groups whose working conditions improved over time: group I (1940-66, n = 180), group II (1967-76, n = 1317), and group III (1977-96, n = 2137). RESULTS: Respiratory symptoms were significantly related to spirometric abnormalities, smoking, and latency time. Breathlessness, in particular, was also associated with age, pleural abnormality and increased cumulative exposure to asbestos fibres. The odds ratios (OR) for parenchymal and/or non-malignant pleural disease were significantly lower in groups II and III compared to group I subjects (0.29 (0.12-0.69) and 0.19 (0.08-0.45), respectively), independent of age and smoking status. Similar results were found when groups were compared at equivalent latency times (groups I v II: 30-45 years; groups II v III: 20-25 years). Ageing, dyspnoea, past and current smoking, and radiographic abnormalities were associated with ventilatory impairment. Lower spirometric values were found in groups I and II compared to group III: lung function values were also lower in higher quartiles of latency and of cumulative exposure in these subjects. CONCLUSIONS: Progressive improvement in occupational hygiene in a developing country is likely to reduce the risk of non-malignant consequences of dust inhalation in asbestos miners and millers.

Risk factors for bronchial hyperresponsiveness in late childhood and early adolescence.

The prevalence of asthma and bronchial hyperresponsiveness (BHR) tends to decrease in male children but increase in female children in the transition from childhood to adolescence. Hormonal factors may be involved in the natural history of asthma during this period. In a prospective study of Montreal school children, the authors examined the determinants of BHR according to the child's pubertal status; 156 male children and 168 female children without a prior diagnosis of asthma were followed for an average of 4.6 yrs. Average age at follow-up was 13.4 yrs and 59% had reached puberty. The prevalence of BHR at follow-up was similar among pre- and postpubertal male children (25.0% versus 29.2%),while BHR was more common among post- compared with prepubertal female children (33.1% versus 14.2%). There were no differences in the determinants (measured in childhood) of BHR at follow-up according to pubertal status. The major determinant of BHR was a positive skin test to dust-mite antigen. BHR was also linked to exposure to gas cooking and the presence of exercise-induced bronchospasm. In conclusion, the results of this study do not support a change in asthma phenotype with the onset of puberty. Pre- and postpuberty, the major determinant of bronchial hyperresponsiveness was skin sensitivity to mite allergen.

Prevalence of vitamin A deficiency in children aged 6-9 years in Wukro, northern Ethiopia.

OBJECTIVE: To determine the prevalence of vitamin A deficiency in children aged 6-9 years in northern Ethiopia. METHODS: A cross-sectional study was carried out and the data were analysed for 824 (61.5%) of 1339 eligible children for whom there was complete information on biochemical vitamin A status, dietary vitamin A intake, ocular examination for xerophthalmia, and anthropometry. FINDINGS: The prevalence of xerophthalmia was 5.8%; serum retinol levels were below 0.35 mumol/l and between 0.35 and 0.70 mumol/l in 8.4% and 51.1% of the children respectively. The liver vitamin A reserve (modified relative dose response ratio > or = 0.06) was low in 41.0% of the children. CONCLUSION: The high prevalence of severe vitamin A deficiency in children aged 6-9 years indicates the need to reevaluate the practice of targeting vitamin A supplementation programmes on children under 6 years of age in areas where vitamin A deficiency is endemic.

Association between vitamin A status and lung function level in children aged 6--9 years in Wukro wereda, Northern Ethiopia.

BACKGROUND: In developing countries, studies using morbidity recalls to evaluate the benefits of vitamin A on respiratory health in children under 6 years of age have been inconclusive. This relationship has not been examined in older children. Spirometric measurements, an objective means of assessing respiratory health, require the subject's collaboration and have been successfully used in children over 6 years of age. This report describes a cross-sectional analysis of the relationship between lung function and vitamin A status in an area endemic to vitamin A deficiency. METHODS: The data on which this report is based were gathered prior to the implementation of a prospective trial of the effect of vitamin A supplementation on lung function level in Northern Ethiopia. Vitamin A status was assessed by the Modified Relative Dose Response (MRDR) method and lung function assessed by spirometry in 702 rural children aged 6--9 years. Demographic, personal health, household, environmental and socioeconomic data were gathered by questionnaire. RESULTS: In children with low vitamin A reserve, the unadjusted forced expiratory volume in one second (FEV(1)) was 48.8 ml (P = 0.006) lower than in those with adequate reserve. This difference was 23.1 ml (P = 0.04) when adjusted for age, gender and height and 14.1 ml (P = 0.20) when adjusted for children's demographic, general health, lung function and household-related characteristics. CONCLUSION: Although these findings suggest that vitamin A plays a relatively minor role in determining FEV(1) level, interpretation is limited by the cross-sectional design. Further clarification of its role requires a trial of vitamin A supplementation.

Prevalence of asthma symptoms among adults aged 20-44 years in Canada.

BACKGROUND: Reported prevalence rates of asthma vary within and between countries around the world. These differences suggest environmental factors in addition to genetic factors in the cause of the disease and may provide clues for preventive strategies. We examined the variability of asthma-related symptoms and medication use among adults in 6 sites across Canada (Vancouver, Winnipeg, Hamilton, Montreal, Halifax and Prince Edward Island) and compared our findings with those from sites that had participated in a recent European survey. METHODS: We used the same sampling strategy and standardized questionnaire as those used in the European Community Respiratory Health Survey (ECRHS). The 6 Canadian sites were selected to represent different environments with respect to climate, air pollution and occupational exposure. Community-based samples of 3000 to 4000 people aged 20-44 years were randomly selected in each site. Subjects were asked to complete the questionnaire by mail between March 1993 and November 1994. Prevalence rates (and 95% confidence intervals [CIs]) of asthma symptoms, self-reported asthma attacks and use of asthma medication were compared across the Canadian sites and with sites that had participated in the ECRHS. RESULTS: The overall response rate of those selected to receive the questionnaire was 86.5% (range 74.5%-92.8%). The prevalence rates of most asthma symptoms varied significantly among the Canadian sites. For instance, 21.9% (Montreal) to 30.4% (Halifax) of the men and 24.0% (Vancouver) to 35.2% (Halifax) of the women reported wheezing in the year before the survey. Depending on the site, 4.4% to 6.3% of the men and 5.2% to 9.5% of the women reported an asthma attack in the last year, and 4.0% to 6.1% of the men and 4.9% to 9.7% of the women were currently using asthma medication. Prevalence rates of symptoms, asthma attacks and medication use did not change with age, but they were higher among women than among men. Compared with the results from the ECRHS sites, those from the Canadian sites were among the highest. INTERPRETATION: Significant variation in the prevalence of asthma symptoms, asthma attacks and use of asthma medication between Canadian sites and international sites suggests environmental influences. Different combinations of factors in different sites may be responsible for the high prevalence rates and should be the subject of further research to guide clinical management and public health intervention.

Occupational asthma in adults in six Canadian communities.

We examined the prevalence, population attributable risk (PAR), and clinical characteristics of occupational asthma (OA) in a randomly selected population in six communities in Canada. Our study followed the European Community Respiratory Health Survey protocol. A randomly selected population of 18,701 (87% response rate) persons from the study communities, ranging in age from 20 to 44 yr, completed an initial questionnaire, of whom 2,974 (39% response rate) attended the laboratory and completed supplementary questionnaires. Of these latter individuals, 383 had asthma. Asthma was defined as physician-diagnosed asthma, and adult-onset asthma was defined as a first attack at age 15 yr or older. We used several methods for estimating OA as follows: (1) reporting of a high-risk job (occupation and industry) for OA at the time of asthma onset (Probable OA); (2) reporting of exposure to a substance that may cause OA (Possible OA) while not in a high-risk job at the time of asthma onset; and (3) combination of the PAR for high-risk jobs and exposures. The prevalence (95% confidence interval [CI]) of Probable OA and Possible OA combined was 36.1% (31.3 to 41.0%) among subjects with adult-onset asthma. The occupations most commonly reported in association with OA were nursing in the Probable OA group and clerical and food preparation in the Possible OA group. The clinical characteristics and exposures reported by both groups were similar. The PAR for adult-onset asthma in high-risk jobs and exposures was 18.2%. The assessment of occupation and industry alone, rather than of exposures, may underestimate the contribution of occupational exposures to asthma prevalence.

Urban-rural differences in questionnaire-derived markers of asthma in Kenyan school children.

Grade 4 Kenyan children attending 10 randomly selected public primary schools in Nairobi (urban) and the Muranga District (rural) were surveyed to establish the prevalence of symptom markers of asthma and to assess the impact of urbanization. A respiratory health and home environment questionnaire was administered at school to parents or guardians. The questionnaire response rates were 94.2% (568/ 603) for Nairobi and 89.6% (604/674) for Muranga. The prevalence rates for asthma, defined as "attacks of shortness of breath with wheeze", were 9.5% for urban and 3.0% for rural children (odds ratio (OR) urban versus rural: 3.42; 95% confidence interval (CI): -1.96-5.91). This urban-rural gradient persisted after adjusting for urban-rural differences in host factors (including duration of breastfeeding and family history of asthma and/or allergy), but was largely explained by urban-rural differences in environmental factors, including indoor animals, sharing a bedroom with a smoker, parental education, house ventilation and exposure to motor vehicle fumes en route to school (adjusted OR: 1.59; 95% CI: 0.70-3.55). Similar results were obtained for all other symptoms. These findings confirm the clinical impression that asthma is an important illness in Kenya and underline the need for the further study of environmental factors amenable to intervention, particularly in urban areas.

Emergency room visits for respiratory illnesses among the elderly in Montreal: association with low level ozone exposure.

Population-based studies of hospital usage have been used to identify the ongoing adverse impacts of photochemical air pollutants on respiratory health. In this study we examined the relationship between the number of daily emergency room (ER) visits for respiratory illnesses (25 hospitals) and outdoor air pollution in Montreal, Quebec (June-August, 1989-1990). Air pollutants measured included 1- and 8-h maximum ozone (O3) and estimated particulate matter < 2.5 microns in aerometric diameter (PM2.5). Seasonal and day-of-week trends, autocorrelation, temperature, and relative humidity were controlled for in-time series regressions. Although O3 levels never exceeded the U.S. National Ambient Air Quality Standard (NAAQS) of 120 ppb (maximum day, 106 ppb), statistically significant (P < 0.01) relationships were found between respiratory ER visits for patients over the age of 64 and both 1- and 8-h maximum O3 measured 1 day prior to the ER visit day during the 1989 summer: ER visits were 18.7% higher than average (95% Cl, 6.5-30.9%) for a mean increase of 44 ppb O3 (1-h maximum), and 21.8% higher than average (95% Cl, 9.7-33.8%) for a mean increase of 38 ppb O3 (8-h maximum). There was an association between respiratory ER visits for the elderly and estimated PM2.5 lagged 1 day (0.1 visit/microgram/m3 PM2.5, P < 0.07), but this was confounded by both temperature and O3. The only finding for a reference group of nonrespiratory conditions was an inverse association between ER visits for infants and O3, but this was confounded by weather. These findings confirm the impression that while air quality standards may protect the respiratory health of the general population, this is not the case for susceptible subgroups such as the elderly.

The role of domestic factors and day-care attendance on lung function of primary school children.

The results of studies examining the relationship of domestic factors to lung function are contradictory. We therefore examined the independent effects of maternal smoking during pregnancy, exposure to environmental tobacco smoke (ETS), the presence of a cat, type of heating and cooking used in the home and day-care attendance on lung function after controlling for socioeconomic status (SES). Nine hundred and eighty-nine children from 18 Montreal schools were studied between April 1990 and November 1992. Information on the child's health and exposure to domestic factors was collected by questionnaire. Spirometry was performed at school. The data were analysed by multiple linear regression with percent predicted FEV1, FVC, and FEV1/FVC as dependent variables. In the overall sample (both sexes combined), cat in the home (regression coefficient, beta = -1.15, 95% confidence interval, CI: -2.26-(-)0.05) and electric baseboard units (beta = -1.26, 95% CI: -2.39-(-)0.13) were independently associated with a lower FEV1/FVC, while day-care attendance (beta = -2.05, 95% CI: -3.71-(-)0.40) significantly reduced FEV1. Household ETS was significantly associated with increasing level of FVC (beta = 2.86, 95% CI: +0.55 to +5.17). In boys but not girls, household ETS (beta = -2.13, 95% CI: -4.07-(-)0.19) and the presence of a cat (beta = -2.19, 95% CI: -3.94-(-)0.45) were associated with lower FEV1/FVC. By contrast, day-care attendance was associated with lower FEV1 (beta = -2.92, 95% CI: -5.27-(-)0.56) and FEV1/FVC (beta = -1.53, 95% CI: -2.73-(-)0.33) in girls only. In conclusion, the results provide evidence that domestic factors and day-care attendance primarily affected airway caliber and gender differences were apparent in the effects of these factors.

Prevalence of exercise induced bronchospasm in Kenyan school children: an urban-rural comparison.

BACKGROUND: Higher rates of exercise induced bronchospasm (EIB) have been reported for urban than for rural African schoolchildren. The change from a traditional to a westernized lifestyle has been implicated. This study was undertaken to examine the impact of various features of urban living on the prevalence of EIB in Kenyan school children. METHODS: A total of 1226 children aged 8-17 years attending grade 4 at five randomly selected schools in Nairobi (urban) and five in Muranga district (rural) underwent an exercise challenge test. A respiratory health and home environment questionnaire was also administered to parents/guardians. This report is limited to 1071 children aged < or = 12 years. Prevalence rates of EIB for the two areas were compared and the differences analysed to model the respective contributions of personal characteristics, host and environmental factors implicated in childhood asthma. RESULTS: A fall in forced expiratory volume in one second (FEV1) after exercise of > or = 10% occurred in 22.9% of urban children and 13.2% of rural children (OR 1.96, 95% CI 1.41 to 2.71). The OR decreased to 1.65 (95% CI 1.10 to 2.47) after accounting for age, sex, and host factors (a family history of asthma and breast feeding for less than six months), and to 1.21 (95% CI 0.69 to 2.11) after further adjustment for environmental factors (parental education, use of biomass fuel and kerosene for cooking, and exposure to motor vehicle fumes). CONCLUSIONS: The EIB rates in this study are higher than any other reported for African children, even using more rigorous criteria for EIB. The study findings support a view which is gaining increasing credence that the increase in prevalence of childhood asthma associated with urbanisation is the consequence of various harmful environmental exposures acting on increasingly susceptible populations.

Effects of air pollution on emergency room visits for respiratory illnesses in Montreal, Quebec.

As an approach to evaluating the public health burden from current air pollution levels, we examined the relationship of daily emergency room (ER) visits for respiratory illnesses (25 hospitals, average 98 visits/d) to air pollution in Montreal, Canada, from June through September, 1992 and 1993. Air pollutants measured included ozone (O3), particulate matter diameter < 10 microm (PM10) and < 2.5 microm (PM2.5), the sulfate fraction of PM2.5 (SO4), and aerosol strong acidity (H+). Temporal trends, autocorrelation, and weather were controlled for in time-series regressions. For 1992, no significant associations with ER visits were found. However, 33% of the particulate data were missing. For 1993, 1-h maximum O3, PM10, PM2.5, and SO4 were all positively associated with respiratory visits for patients over 64 yr of age (p < 0.02). An increase to the mean level of 1-h maximum O3 (36 ppb) was associated with a 21% increase over the mean number of daily ER visits (95% confidence interval [CI]: 8 to 34%). Effects of particulates were smaller, with mean increases of 16% (4 to 28%), 12% (2 to 21%) and 6% (1 to 12%) for PM10, PM2.5, and SO4, respectively. Relative mass effects were PM2.5 > PM10 >> SO4. Ozone and PM10 levels never exceeded 67 ppb and 51 microg/m3, respectively (well below the U.S. National Ambient Air Quality Standards of 120 ppb and 150 microg/m3, respectively). The present findings have public health implications with regard to the adverse health effects of urban photochemical air pollution on older individuals.

Exercise-induced bronchospasm: a pilot survey in Nairobi school children.

Exercise-induced bronchospasm (EIB), a common feature of asthma in children, has been used as the outcome measure in community-based surveys of childhood asthma to circumvent difficulties arising from relative lack of objectivity in the use of questionnaires in communities with different cultural and language orientations. We report here the results of the first community-based study of childhood asthma in Kenya using EIB as the outcome measurement. The data was collected in a pilot study to develop methodology for a larger subsequent study. The survey targeted grade four children in five Nairobi City Council school each representing a neighbourhood social economic status (SES). Out of 597 eligible, 408 children took part in the study (68% participation rate). EIB defined as decline in FEV1 of 15% or more, post-exercise was found in 10.5% (95% CI; 10.3, 10.7) of the children studied, the highest rate reported so far in Africa. While boys were more likely to exhibit EIB compared to girls, the prevalence of EIB tended to decrease with age, especially among children residing in low SES neighbourhoods where the EIB prevalence rates tended to be lower compared to those among children from higher SES neighbourhoods. However, none of these differences was statistically significant. This study confirms the feasibility of undertaking exercise challenge tests in the African context and we recommend that additional studies of similar nature be carried out in other populations of Africa to explore the potential of using an exercise test as a marker of asthma in epidemiologic studies.

Relationship between chronic dyspnea and expiratory flow limitation in patients with chronic obstructive pulmonary disease.

The purpose of this study was to assess whether expiratory flow limitation (FL), as measured by applying negative pressure at the mouth during tidal expiration, is a better predictor of dyspnea than routine spirometry measurements. The study population consisted of 117 ambulatory patients with COPD. Dyspnea was assessed according to the ATS-DLD respiratory Questionnaire. Expiratory flow limitation was measured in supine and sitting positions, and expressed as a percentage of the expired control tidal volume affected by flow limitation (FL, % VT). Using Spearman's rank correlation (rs), we found that the correlation of dyspnea scale with FL was stronger (rs > 0.5) than with FVC (rs < -0.3) or FEV1 (rs < -0.4) in both positions. In a multiple regression analysis FL remained the best predictor of dyspnea scale even after adjustment for FEV1 (% pred). Finally, FL was almost as sensitive as FEV1 (% pred) but much more specific in assessing the severity of dyspnea scale. These findings suggest that expiratory flow limitation as measured by the negative expiratory pressure technique may be more useful in the evaluation of dyspnea in patients with COPD than spirometry measurements.