Why study the epidemiology of asthma?

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.

Wheat sensitization and work-related symptoms in the baking industry are preventable. An epidemiologic study

A cross-sectional study was conducted among 393 workers from 21 bakeries to study the relationship between wheat allergen exposure and wheat sensitization and work-related allergic symptoms. Exposure to wheat allergens was characterized by a recently developed and validated immunoassay. Specific IgE antibodies against wheat flour and common allergens were measured by immunoassays, and work-related allergic symptoms were registered by questionnaire. A strong and positive association was found between wheat flour allergen exposure and wheat flour sensitization. This relationship was steepest and strongest in atopics. Prevalence ratios for high and medium wheat allergen exposure were 5.2 (95% confidence interval [CI], 1.6-16.2), and 2.7 (0.5-14.5) for atopic workers, and 2.5 (0.8-7.5) and 1.4 (0. 3-6.4) for nonatopics, compared with workers with low wheat allergen exposure. In sensitized bakers those with an elevated allergen exposure had more often work-related symptoms, with prevalence ratios for high and medium wheat allergen exposure of 3.5 (CI 1.6-7. 5) and 2.6 (CI 0.9-7.8), respectively, compared with workers with low wheat allergen exposure. The existence of exposure-sensitization gradients suggests that work-related sensitization risk will be negligible when exposure levels will be reduced to average exposure concentration of 0.2 microgram/m3 wheat allergen or approximately 0.5 mg/m3 inhalable dust during a work shift.

SAPALDIA: methods and participation in the cross-sectional part of the Swiss Study on Air Pollution and Lung Diseases in Adults

SAPALDIA--the Swiss Study on Air Pollution and Lung Diseases in Adults--focuses on the long term health effects of low to moderate levels of air pollutants as typically seen in different parts of Switzerland. The aim of the SAPALDIA cross-sectional study carried out in 1991 was to determine the prevalence of bronchial asthma, chronic bronchitis and allergic conditions in the adult population of Switzerland and to identify and to determine the respective importance of potentially influencing factors. These could be both personal (smoking habits, allergy status, family history, occupation) and environmental (outdoor and indoor pollution, aeroallergens, climate). A further aim of the cross-sectional study consisted in the identification of individuals susceptible to present symptoms during a two year observation period and to be included in the SAPALDIA follow-up study. This technical report represents the methodological documentation for the cross-sectional study of SAPALDIA. The instruments and the methods of standardisation are presented and discussed. The medical examination consisted of a computerised interview using a standardised questionnaire, the taking of a blood sample for serological tests, allergy skin testing, the measurement of end expiratory CO and body height, and pulmonary function testing followed by methacholine challenge testing or bronchodilatation testing. The pattern of participation and the 9651 participants of the study, representing 59.3% of the sample, are described. Based on information on non-participants gained by telephone interviews and mailed short questionnaires, possible selection biases are quantified and discussed.

Observations on asthma

A review of the present understanding of asthma leads to the following conclusions: an elevated IgE is the principal risk factor in the development of childhood asthma; secondary exposure to a wide range of environmental agents (including indoor bioallergens) accounts for the variations in prevalence; prevalence (defined by a positive answer to the question "Have you ever had doctor-diagnosed asthma?") ranges between 4 and 8% in children. Black children have a slightly higher prevalence than white children in the United States, and in both races boys have a higher prevalence than girls. A high prevalence is found in Puerto Rican children in the United States. Patterns of utilization of health care resources (hospital emergency departments, individual physicians, etc.) are dependent on economic circumstances. Low-income children have higher annual morbidity (days in hospital, days off school, etc.) than higher income children and are more dependent on hospital emergency departments for primary care. Relatively little is known about nonatopic asthma in adults, although virus infections and occupational exposures play some part in its induction. There are some striking examples of asthma attack periodicity, and much may be learned from these. Hospital admissions for asthma have increased in many regions over the past 15 years; it is unlikely that this represents the increased admission of milder cases and hence would indicate that asthma has become more severe. This is likely to be a more sensitive indicator of change than mortality. Associations between indices of health effects and air pollutants indicate that these are probably playing a role in the worsening of asthma. Adverse effects related to SO2 and NO2 exposures have been documented, and fine particulate pollution (PM10) is also associated with worsening of asthma. Ozone is an intense respiratory irritant, and, together with acid aerosols, may well be playing a role in the worsening of asthma. It is not known whether any of these agents are affecting prevalence.

[An analysis of the prevalence of respiratory symptomatology in the general population]

This paper is a report of a cross-sectional epidemiological study that formed part of multicenter European project; the aim was to estimate the prevalence of respiratory symptoms and signs related to asthma over a period of 12 months in the city of Seville. A sample of 4,000 persons of both sexes, aged between 20 and 44 years old, was surveyed first by mail questionnaire and later by telephone interview. We analyzed the response index obtained with the mail survey for the epidemiological study of asthma in the area and for the frequency of respiratory symptoms and their distribution by age and sex. The response index was 53.36% and was similar for men and for women. Forty-nine percent reported at least one respiratory symptom, with nocturnal coughing attacks (27.7%) and wheezing (22.2%) being the most frequent. The frequency of these symptoms was different by sex, however, with the former more often reported by women (p < 0.02) and the latter by men (p < 0.001). We found that 14.9% of the population had rhinitis and that women reported this symptom more often (p < 0.02). Symptoms related to asthma were nocturnal attacks of breathlessness, the use of asthma medication and an asthma attack diagnosed by a physician within the last 12 months. With these criteria the estimated prevalence of asthma was 11.72%, a proportion that held steady for all age groups except the middle-aged and for both sexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Total population survey of the frequency and severity of asthma in 17 year old boys in an urban area in Israel

BACKGROUND

There is evidence that the prevalence of asthma in children and young people is increasing.

METHODS

An examination of a total population (35,170) of 17 year old Jewish boys of one seaside urban area in Israel was undertaken during two years, 1986 and 1990, by trained respiratory physicians in a regional recruiting office of the Israel Defence Forces. All boys who had ever been diagnosed as having asthma or symptoms that could have been due to asthma underwent a further examination by respiratory physicians that included spirometry at rest. A test to evaluate exercise induced asthma was performed on a treadmill in 88% of the boys.

RESULTS

Lifetime prevalence (asthma in the past or at present) increased from 7.9% in 1986 to 9.6% in 1990. Point prevalence (current asthma) increased from 5.0% to 5.9%. The prevalence of current asthma increased in all degrees of severity (mild disease from 3.3% to 3.7%, moderate disease from 1.7% to 2.2%, and severe disease from 0.03% to 0.04%). By the age of 17, 77.4% of boys who had suffered from asthma had no or only very mild symptoms.

CONCLUSIONS

It is considered that the measured increase in prevalence of asthma from 1986 to 1990 reflects a true increase among the Jewish Israeli population.

Risk factors of soybean epidemic asthma. The role of smoking and atopy

Epidemics of emergency room admissions for asthma occurring in Barcelona during the period 1981 to 1987 were caused by inhalation of soybean dust. To investigate the risk factors that determined why some asthma patients became reactive to soybean and were consequently affected by the asthma epidemics of Barcelona but others did not do so, a case-control study was conducted during 1989, 2 yr after the cessation of asthma epidemics. Patients with asthma admitted in emergency room services during epidemic asthma days (n = 169) were compared with asthma patients admitted in the same services during nonepidemic days and who were never admitted during the epidemics (n = 147). Risk factors other than soybean exposure, namely skin reactivity against at least one common allergen (odds ratio [OR] 3.0, 1.7 to 5.3), age over 64 yr (OR 2.8, 1.4 to 6.0), cigarette smoking at the time of the epidemics (OR 2.3, 1.2 to 2.4), past smoking (OR 1.8, 0.9 to 3.7), and total immunoglobulin E (IgE) higher than 100 IU/ml (OR 1.7, 1.0 to 3.0), were found independently related to epidemic asthma. The role of smoking was especially important for those who had a positive skin reaction and were exposed to soybean dust (OR 7.9, 1.8 to 36.0). In this group, a dose-response pattern with pack-years was observed (p less than 0.01). The present findings suggest a multifactorial process for epidemic asthma, in which atopy and cigarette smoking played an important synergistic role. This has a preventive potential for IgE-related asthma.

Assessment and prediction of asthma and its severity in the pediatric community

Seventy four asthmatic children aged 7 to 11 years were examined along with controls matched by age and sex. Clinical and laboratory investigations preceded a 28-day follow-up where data about morning and evening peak expiratory flow rate (PEF), symptoms and treatment were recorded. The coefficient of variation of PEF was found to be an objective measurement of asthma severity that has statistically significant correlation with both symptoms (rs = .36) and treatment (rs = .60). Moreover, it separates mild and severe asthmatics, as confirmed by statistically significant differences (p = .008 or less) in symptoms, treatment, skin allergy and airways response to exercise. Skin allergy and airways responsiveness to exercise were found to be predictors of both disease and severity. By means of logistic regression analysis it was possible to establish the probabilities for both asthma and severe asthma when children presenting and not presenting these characteristics are compared. One single positive skin test represent a probability of 88% for the development of asthma and a probability of 70% for severe disease. A PEF reduction of 10% after an exercise test implies a probability of 73% for disease and a probability of 64% for severe disease. Increases in these variables imply geometrically increased risks and their presence together have a multiplicative effect in the final risk.

Genetics of asthma and hay fever in Australian twins

The occurrence of self-reported asthma/wheezing and hay fever among 3,808 pairs of twins from the Australian National Health and Medical Research Council Twin Registry was examined for evidence of genetic transmission by path analytic methods. The cumulative prevalence of asthma or wheezing was 13.2% and of hay fever, 32%. There were significant correlations in liability to reported disease among twins, and these were higher in monozygotic twins (MZ) (r = 0.65) than in dizygotic twins (DZ) (r = 0.25), and in male MZ twins (r = 0.75) compared with female MZ twins (r = 0.60). Analysis under the assumptions of the classic twin model suggested that there were genetic factors common to asthma and hay fever, with a correlation in genetic liability to the traits of 0.52 for men and 0.65 for women. These genes acted substantially in a nonadditive fashion in men but not in women. As the genetic correlation was significantly less than unity, this implied additional genetic factors influencing either or both diseases individually. The estimated heritability of these diseases was 60 to 70% in this population. Environmental causes of both diseases also were correlated (r = 0.53 for men and 0.33 for women). Cigarette smoking was only weakly associated with wheezing.

Tolerance to reduction of oral steroid dosage in severely asthmatic patients receiving nedocromil sodium

We examined the efficacy of nedocromil sodium as an oral steroid sparing agent in a group of 37 severe, oral steroid-dependent asthmatics. All were receiving daily or alternate-day prednisone. These patients had taken part in an earlier, 12-week double-blind trial of nedocromil sodium 16 mg daily by inhalation or matching placebo. They continued with test treatment (26 patients on nedocromil sodium and 11 on placebo) on a double-blind basis for a further 12 weeks. During this time, patients visited the clinic every 2 weeks, when asthma severity and symptoms were assessed. On the basis of these assessments, the dose of oral steroid was either decreased, or maintained at the same level, or the patient was withdrawn if the asthma had deteriorated to a clinically unacceptable level. The nedocromil sodium group was able to achieve a greater percentage reduction in oral steroid dose (P less than 0.05). The rate of withdrawal due to worsening asthma was 31% from active and 55% from placebo treatment. Trends in other variables (time before withdrawal and numbers of patients able to withstand complete removal of oral steroids) favoured nedocromil sodium but the differences between the groups were not statistically significant.