Ethnic differences in prevalence of asthma symptoms and bronchial hyperresponsiveness in New Zealand schoolchildren

[Childhood asthma and risk factors]

INTRODUCTION

This article summarizes the contribution of epidemiology to the understanding of childhood asthma. The first task in epidemiology is to determine prevalence and incidence of any disease.

PREVALENCE

Epidemiological investigations are aimed at evaluating hypotheses about causes of disease by defining demographic characteristics of a certain population as well as by determining possible effects of environmental factors. In spite of some limitations, data obtained by epidemiological investigations have been valuable in confirming both the increasing incidence of asthma and the differences in prevalence in certain population groups. The observance of this phenomenon has led to much speculation and a lot of attempts to identify the reasons behind the rising prevalence.

RISK FACTORS

Epidemiological studies have identified risk factors for the development of childhood asthma and provided insight into natural history of disease and prognosis. Factors ranging from increased numbers of immunizations to increased air pollution have been suggested, but subsequent analysis has failed to provide the supporting evidence to implicate most of these possibilities. The concept known as the hygiene hypothesis has gained some support from epidemiological studies.

CONCLUSION

The development of asthma as well as its severity are affected by numerous factors and their interactions can he explained by the heterogeneous nature of this disease.

Comparison of mannitol and methacholine to predict exercise-induced bronchoconstriction and a clinical diagnosis of asthma

BACKGROUND

Asthma can be difficult to diagnose, but bronchial provocation with methacholine, exercise or mannitol is helpful when used to identify bronchial hyperresponsiveness (BHR), a key feature of the disease. The utility of these tests in subjects with signs and symptoms of asthma but without a clear diagnosis has not been investigated. We investigated the sensitivity and specificity of mannitol to identify exercise-induced bronchoconstriction (EIB) as a manifestation of BHR; compared this with methacholine; and compared the sensitivity and specificity of mannitol and methacholine for a clinician diagnosis of asthma.

METHODS

509 people (6-50 yr) were enrolled, 78% were atopic, median FEV1 92.5% predicted, and a low NAEPPII asthma score of 1.2. Subjects with symptoms of seasonal allergy were excluded. BHR to exercise was defined as a > or = 10% fall in FEV1 on at least one of two tests, to methacholine a PC20 < or = 16 mg/ml and to mannitol a 15% fall in FEV1 at < or = 635 mg or a 10% fall between doses. The clinician diagnosis of asthma was made on examination, history, skin tests, questionnaire and response to exercise but they were blind to the mannitol and methacholine results.

RESULTS

Mannitol and methacholine were therapeutically equivalent to identify EIB, a clinician diagnosis of asthma, and prevalence of BHR. The sensitivity/specificity of mannitol to identify EIB was 59%/65% and for methacholine it was 56%/69%. The BHR was mild. Mean EIB % fall in FEV1 in subjects positive to exercise was 19%, (SD 9.2), mannitol PD15 158 (CI:129,193) mg, and methacholine PC20 2.1(CI:1.7, 2.6) mg/ml. The prevalence of BHR was the same: for exercise (43.5%), mannitol (44.8%), and methacholine (41.6%) with a test agreement between 62 & 69%. The sensitivity and specificity for a clinician diagnosis of asthma was 56%/73% for mannitol and 51%/75% for methacholine. The sensitivity increased to 73% and 72% for mannitol and methacholine when two exercise tests were positive.

CONCLUSION

In this group with normal FEV1, mild symptoms, and mild BHR, the sensitivity and specificity for both mannitol and methacholine to identify EIB and a clinician diagnosis of asthma were equivalent, but lower than previously documented in well-defined populations.

TRIAL REGISTRATION

This was a multi-center trial comprising 25 sites across the United States of America.

Asthma prevalence in European, Maori, and Pacific children in New Zealand: ISAAC study

The International Study of Asthma and Allergies in Childhood (ISAAC) demonstrated that the highest prevalence of asthma in the world is in English-speaking countries, including New Zealand. In this paper, we compare asthma symptom prevalence in the three major ethnic groups (Maori, Pacific, and European) in the six participating centers in New Zealand. Hospital admission rates for asthma are higher among Maori and Pacific children compared to European children. The working hypothesis was that there were important differences in prevalence of asthma symptoms or diagnosis between ethnic groups which might explain these observed differences in asthma morbidity. In each center in 1992-1993, we sampled approximately 3000 children at each of the age brackets 6-7 years and 13-14 years. There were 37592 participants. Maori children had higher rates of diagnosed asthma and reported asthma symptoms than Pacific children in both age groups (diagnosed asthma in 6-7-year-olds: Maori, 31.7%; Pacific, 21.2%; 95% confidence interval on difference (CID), 7.2, 13.8; P < 0.001; 13-14-year-olds: Maori, 24.7%; Pacific, 19.2%; CID 2.5, 8.5; P < 0.001; recent wheeze in 6-7-year-olds: Maori, 27.6%; Pacific, 22.0%; CID, 2.6, 8.6; P < 0.001; 13-14-year-olds: Maori, 30.8%; Pacific, 21.1%; CID, 4.8, 14.5; P < 0.001;). European children had rates intermediate between those of Maori and Pacific children (6-7-year-olds) or similar to those of Maori children (13-14-year-olds), but had the lowest prevalence of night waking with wheeze in both age groups (e.g., 6-7-year-olds: European, 2.6%; Maori, 5.8%; Pacific, 5.7%; European-Maori CID: -4.2, -2.2, P < 0.001; European-Pacific CID: -4.7, -1.7, P < 0.001; Maori-Pacific CID: -1.7, 1.8, P = 1.0). The pattern of differences closely resembled that in a 1985 Auckland study, despite a 1.5-1.7-fold overall increase in prevalence. In conclusion, there are important differences in asthma prevalence among Maori, Pacific, and European children. These differences are small compared to worldwide variation, but their pattern is stable over time. The higher rate of severe asthma symptoms that Maori and Pacific children report may be one reason for the increased asthma morbidity in these groups. Further studies are needed to determine the reasons for these apparent differences in asthma severity.

Very low birthweight and asthma by age seven years in a national cohort

Several studies have suggested that very low birthweight (VLBW < 1500 g) is associated with increased rates of respiratory problems in childhood and that the presence of chronic lung disease further increases the risk. We aimed to assess rates of asthma at 7-8 years of age in a national cohort of VLBW infants born in 1986 and for whom perinatal data were available. Two hundred ninety-nine former VLBW children (96% of surviving children living in New Zealand) were assessed at a home visit. Parents were asked a comprehensive questionnaire, including three questions aimed at assessing morbidity from asthma: 1) was the child diagnosed as having asthma before age 7 years; 2) was the child still experiencing asthma at the age of 7 years; and 3) was the child prescribed daily medication for asthma at the age of 7 years. Overall, 50% of the cohort had been diagnosed with asthma before age 7, compared with 27% of a sample of New Zealand children assessed contemporaneously in an international study; 32% had asthma at age 7, and 11% were taking daily medication. All three categories of asthma were associated with a family history of asthma, but there was no association with any perinatal factors. A diagnosis of asthma before age 7 was more likely when the mother smoked in pregnancy (P < 0.005) and currently smoked (P < 0.01), and trended so when parents lacked high school qualifications and in Maori or Pacific Island families (P < 0.10). In contrast, daily medication was more frequent when parents had educational qualifications and in non-Maori or Pacific Island families (P < 0.05). On multiple logistic regression, a family history of asthma was a significant predictor for any and current asthma (P < 0.001) and daily medication (P < 0.05); maternal smoking in pregnancy was a significant predictor for any asthma (P < 0.05); and non-Maori or Pacific Island ethnicity was a significant predictor for asthma treatment (P < 0.05). We conclude that rates of childhood asthma are high in this VLBW cohort, but the high prevalence appears to be unrelated to perinatal factors, including respiratory morbidity. There are suggestions that social factors contribute to both asthma risk and treatment.

Increased nitric oxide production in the respiratory tract in asymptomatic pacific islanders: an association with skin prick reactivity to house dust mite

BACKGROUND

Exhaled nitric oxide (NO) is increased in asthma and may also be increased in subclinical airway inflammation. The relationship between atopy and subclinical airway inflammation in the pathogenesis of asthma remains unclear. We have evaluated the relationship between exhaled NO levels and skin prick test reactivity to 8 common allergens in 64 asymptomatic adult Pacific Islanders. Pacific Islanders were studied as a racial group with major morbidity from asthma.

OBJECTIVE

Our purpose was to determine whether asymptomatic subjects with skin prick test reactivity to common allergens have elevated NO levels.

METHODS

All subjects underwent full lung function testing and skin prick testing. Exhaled and nasal NO levels were measured by chemiluminescence (Logan LR2000 analyzer) with use of the single-breath and breath-holding techniques, respectively.

RESULTS

House dust mite (HDM) reactivity was seen in 38 of 64 (56%). Exhaled NO levels (median 8.9 ppb, range 2.9-47.3 ppb) and nasal NO levels (527.5 +/- 181.5 ppb) lay above the normal European range in 30% and 25% of subjects, respectively. HDM reactivity was associated with higher exhaled NO levels (P <. 0005) and higher nasal NO levels (P =.01). In HDM-sensitive subjects the wheal size for HDM correlated with exhaled NO levels (r = 0.35, P =.04) and nasal NO levels (r = 0.40, P =.01). On multivariate analysis, exhaled NO levels were independently and positively related to the severity of HDM reactivity (P =.01) and nasal NO levels (P <.02), equation R(2) = 0.27.

CONCLUSION

NO levels are elevated in a significant proportion of asymptomatic Pacific Islanders and are associated with HDM sensitivity. This may denote subclinical airway inflammation in this population and suggests that exposure to HDM in atopic individuals might play an important role in the early pathogenesis of asthma.

Geographical and socioeconomic variation in the prevalence of asthma symptoms in English and Scottish children

BACKGROUND

There has been controversy over the relation between poverty and asthma in the community. The aim of this analysis was to disentangle geographical and socioeconomic variation in asthma symptoms.

METHODS

The analysis is based on parental reports of symptoms from data collected in 1990 and 1991. Children aged 5-11 years from three populations (English representative sample, Scottish representative sample, and an English inner city sample) were included. Of 17 677 eligible children, between 14 490 (82.0%) and 15 562 (88.0%) children were available for analysis according to symptom group.

RESULTS

Wheezy symptoms were less prevalent in the Scottish sample than in the English samples and asthma attacks were most prevalent in the English representative sample. Asthma attacks were less prevalent in inner city areas than in the English representative sample (OR 0.79, 95% CI 0.66 to 0.95), but persistent wheeze and other respiratory symptoms were more prevalent (OR 1.95, 95% CI 1.65 to 2.32 and OR 1.67, 95% CI 1.52 to 1.84, respectively). The prevalence of persistent wheeze was higher in children whose father's social class was low and in those living in areas with a high Townsend score (an index of poverty) than in other children (p<0.001). Of the 14 areas with the highest Townsend score, 13 had an OR above 1 and six had an OR significantly higher than the reference area.

CONCLUSIONS

Persistent wheeze is more prevalent in poor areas than in less deprived areas. This may indicate that poverty is associated with severe asthma or that a high percentage of persistent asthma symptoms in inner city areas are unrecognised and untreated.

Variations in hospitalization rates for asthma among black and minority ethnic communities

In response to the introduction of ethnic monitoring within the U.K. hospital inpatient data set, this study investigates the variations in secondary healthcare utilization by Black and minority ethnic communities whose cause of admission is related to asthma. The study examines all residents of the West Midlands: over 5 million people, of whom 8.5% are from Black and minority ethnic groups. A retrospective study of 15,921 asthma-related hospital admissions, from 1 April 1995 to 31 March 1996, was carried out. Age-standardized admission rates were higher in all Black and minority ethnic groups studied than in the White group. There were elevated rates in Black children aged 5-14 years, and particular differences were observed for Indian and Bangladeshi men and women aged 65 years or over. Emergency admissions to hospital for asthma were strongly associated with patients' socioeconomic background but this was largely observed for Black and minority ethnic groups that also generally experience high levels of deprivation. The findings support previous studies which suggest that hospital utilization rates for asthma among people from Black and minority ethnic groups are high compared with the White group, despite little evidence in measured prevalence. This study suggests that ethnic background is more important in asthma admissions than deprivation, which raises serious concerns on the appropriateness and quality of asthma care for these patient groups within our society. Future studies need to examine pathways to care, that is the health-seeking behaviour of Black and minority ethnic groups, the type of treatment received at the primary care level and referral patterns to secondary care.

Peak flow variability, methacholine responsiveness and atopy as markers for detecting different wheezing phenotypes in childhood

BACKGROUND

There is increasing evidence that wheezing during childhood may be a heterogeneous condition, and that different forms of wheezing may be associated with different risk factors and prognosis. The aim of this study was to determine if measures of airway lability and of atopy could identify distinct wheezing phenotypes during childhood.

METHOD

In a cohort of children followed from birth peak flow variability (n = 600) was evaluated and methacholine challenge responsiveness (n = 397) was measured at age 11 in relation to wheezing before the age of three, and at age six and 11 years total serum IgE and skin test reactivity to allergens were determined.

RESULTS

Neither positive peak flow variability nor methacholine hyperresponsiveness measured at age 11 were associated with wheezing occurring only during the first three years of life. Both methacholine hyperresponsiveness and positive peak flow variability were associated with wheezing at both ages six and 11 (OR 5.1 (95% CI 2.4 to 10.6) and 2.3 (1.2 to 4.5), respectively). In addition, positive peak flow variability was associated with wheezing up to the age of six but not at age 11 in non-atopic children (OR 2.9 (95% CI 1.0 to 8.8)). Methacholine hyperresponsiveness measured at age 11 was more frequently observed in boys (OR 2.1 (95% CI 1.2 to 3.5)) and was strongly associated with serum IgE levels measured at ages six and 11 (p < 0.001) and with positive skin test reactivity (OR 4.5 (95% CI 2.0 to 10.1)). Peak flow variability was unrelated to sex or markers of atopy (IgE and skin test reactivity).

CONCLUSIONS

Methacholine responsiveness and peak flow variability assessed at age 11, together with markers of atopy (IgE and skin test reactivity to allergens) identify three different wheezing phenotypes in childhood: "transient early wheezing" limited to the first three years of life and unrelated to increased airway lability; "non-atopic wheezing" of the toddler and early school years associated with positive peak flow variability but not with methacholine hyperresponsiveness; and "IgE-associated wheeze/asthma" associated with persistent wheezing at any age and with methacholine hyperresponsiveness, peak flow variability, and markers of atopy.

Asthma management and mode of acquisition of inhaled bronchodilators

BACKGROUND

Controversy has existed about the benefits and disadvantages associated with the availability of inhaled bronchodilators over the counter (OTC).

AIMS

To compare sociodemographic features, use of preventive medications, use of medical services and control of asthma in adults who purchased inhaled bronchodilators OTC with those who purchased on prescription (script).

METHODS

A cross-sectional telephone survey of 772 adults 18 years and over who used inhaled bronchodilators for their asthma. Symptoms, asthma medications, and management practices were determined by a structured questionnaire administered by trained telephone interviewers.

RESULTS

Two hundred and thirty adults purchased their bronchodilator OTC and 542 on script. OTC purchasers were more likely to be male (OR: 1.5), have had tertiary education (1.5) and be in paid employment (2.8); they were less likely to report frequent symptoms (wheeze, nocturnal symptoms or EIA more than once a week) (0.71); were less likely to use preventive medications more than twice a day (0.57) and were less likely to have consulted a general practitioner in the previous year (0.38). However, poor control of asthma symptoms was evident in both OTC and script groups. Forty per cent of the OTC group who had symptoms more than two to three times a week and 34% of the script group were not using preventive medication.

CONCLUSIONS

Undertreatment and suboptimal management of asthma were apparent in both OTC and script groups.

Major reduction in asthma morbidity and continued reduction in asthma mortality in New Zealand: what lessons have been learned?

Increasing financial barriers to primary health care against a background of social and economic decline are likely to have contributed to asthma morbidity and mortality in New Zealand. Although there would not have been a sufficient increase in asthma prevalence to have accounted for the threefold increase in mortality rates, whether or not there was an increase in asthma severity in the late 1970s remains open to debate. Misuse or poor use of newly available and potent bronchodilator medications by those with the most severe asthma may simply have contributed to further delays in obtaining appropriate care and therefore to an increase in frequency of severe attacks in the community. Despite substantial increases in the use of bronchodilator therapy in New Zealand, there was no immediate improvement in indices of either asthma morbidity or mortality. The initial reduction in mortality rates in the 1980s happened at a time when first admissions for asthma were still increasing and seems to be best explained by an improvement in utilisation of hospital services (which were free until 1992) rather than a reduction in asthma severity. However, the recent reductions in all measures of asthma morbidity and further reduction in asthma mortality since 1989 does now suggest a reduction in asthma severity and would be best explained by the substantial increase in medium and high dose inhaled corticosteroid use, and to the endorsement of the current management strategies for asthma which are being promoted internationally and which were given considerable publicity in New Zealand in 1989 and 1990. Whilst sales of inhaled beta agonists were higher in 1991 than 1989, this may not reflect their pattern of use by individual patients since the need for an increase in inhaled beta agonist treatment has been accepted as indicating a lack of control and the need for either starting or increasing the dose of inhaled steroid treatment.

Prevalence, severity and medical management of asthma in European school children in 1985 and 1991

This present study, conducted in 1991, examined trends in the prevalence, severity and medical management of asthma in European school children by repeating the protocol of a study performed in 1985, using the same schools and questionnaire. One thousand, nine hundred and one children in 1991 were compared with 1084 children in 1985. The prevalence of respiratory symptoms increased significantly by approximately one-third, although the increase in the diagnostic label 'asthma' did not increase significantly. Asthma severity indices (> 12 asthma attacks in the last 12 months and symptoms in the last month) were not significantly increased, except for night cough in the last month (1985 7.0%, 1991 9.9%, P = 0.008). In 1991, children with wheeze in the last 12 months were more likely to be diagnosed as having asthma and treated with bronchodilators and prophylactic drugs than in 1985. We conclude that the prevalence of asthma symptoms has increased from 1985 to 1991, but the two indices of severity of asthma are mostly unchanged. Diagnosis of asthma in children with symptoms has improved but asthma still appears underrecognized. Drug treatment of asthma has increased.

Dietary sodium intake and the risk of airway hyperreactivity in a random adult population

BACKGROUND

High dietary sodium intake has been identified as a potential cause of asthma and airway hyperreactivity. This study was designed to test the hypothesis that dietary sodium intake is an independent determinant of the risk of hyperreactivity in the general population, and to assess the role of atopy in the association between these factors.

METHODS

Airway reactivity to methacholine, atopy, 24 hour urinary sodium excretion, and self-reported smoking and symptom history were measured in a random sample of 1702 adults aged 18-70 from an administrative district of Nottingham. Hyperreactivity was defined as a PD20FEV1 of 12.25 mumol or less, and atopy was defined quantitatively as the mean allergen skin weal response to Dermatophagoides pteronyssinus, cat fur, and grass pollen, and categorically as the occurrence of any allergen response 1 mm or greater than the saline control. Multiple logistic regression analysis was used to estimate the independent relative odds of hyperreactivity, atopy, or symptoms in relation to sodium excretion in all 1702 subjects, and multiple linear regression to assess the independent relation between sodium excretion and mean allergen skin weal diameter, and the PD20 value amongst hyperreactive subjects.

RESULTS

There was no relation between the relative odds of hyperreactivity to methacholine and 24 hour urinary sodium excretion, either before or after adjustment for age, smoking, allergen skin weal diameter, and sex, and similarly no relation if the analysis was restricted to men or women only. The relative odds of having at least one allergen skin test response 1 mm greater than the saline control were increased in relation to sodium excretion after adjustment for age, sex, and smoking by a ratio of 2.08 (95% CI 1.04 to 4.15) per log10 unit increase in sodium excretion, but there was no evidence of an association between sodium excretion and the occurrence of self-reported wheeze, hay fever, eczema, or asthma. There was no relation between 24 hour sodium excretion and the magnitude of the mean allergen skin weal response or the PD20 value.

CONCLUSIONS

These findings do not support the hypothesis that a high dietary sodium intake is a risk factor for airway hyperreactivity or atopic disease in the general adult population.

Asthma, power, and the therapeutic conversation

Previous research has indicated that family therapy may be of use when a child has chronic, uncontrolled asthma. The significant power relations were considered to be those between the child and the parents. In this article, I examine the wider contextual relations that the family encounters when asthma is a problem, and suggest that these relations are unable to be understood without more thoroughly theorizing power. Because of power relations, the meanings of therapeutic encounters for families and health care professionals may not be consensual. The effect may be to hamper adequate asthma management. I suggest that when Foucault's work is examined alongside that of Hoffman, and Anderson and Goolishian, then the processes that distort these understandings are more readily understood. These ideas are illustrated with examples from a research project.

Hospital admission rates for asthma and pneumonia in Fijian and Indian children

To confirm the clinical impression that Melanesian Fijian and Fiji Indian children differ in their profiles of respiratory morbidity, national hospital admission statistics for respiratory diseases in children aged 5-14 years were examined for 4 years between 1985 and 1989. The mean annual admission rate for asthma was three-fold higher in Indians (1.68/1000) than Fijians (0.56/1000); rate ratio (Indian:Fijian) = 3.00, 95% confidence interval 2.54-3.55. Conversely, the mean annual admission rate for pneumonia was three-fold higher in Fijians (1.70/1000) than Indians (0.50/1000); rate ratio (Fijian:Indian) = 3.39 (2.85-4.03). Admission rates for influenza, tuberculosis and bronchiectasis were also higher in Fijian children. Fijian and Indian children differ in hospital admission rates for respiratory diseases, possibly due to differences in incidence, prevalence or severity.

Effects of time, sex, ethnic origin, and area of residence on prevalence of asthma in Israeli adolescents

OBJECTIVES

To study effects of time, sex, ethnic origin, and area of residence on prevalence of asthma in Israeli adolescents.

DESIGN

Retrospective survey of asthma from computerised medical draft records of conscripts examined up to the end of 1989.

SETTING

Five regional centres in Israel.

SUBJECTS

443 186 conscripts (262 836 males and 180 350 females) aged 17-18 who were born over a nine year period.

MAIN OUTCOME MEASURES

Asthma determined by medical history, physical examination, and lung function tests at rest and after exercise.

RESULTS

Asthma was more prevalent in males than females (26.5/1000 v 21.4/1000, relative risk 1.25 (95% confidence interval 1.19 to 1.32)). Subjects were split into three groups according to year of birth, and prevalence of asthma increased over time from 18/1000 to 24/1000 to 36/1000 (risk of asthma 0.56 (0.54 to 0.59) for first birth group relative to last birth group and 0.69 (0.66 to 0.72) for second group relative to last group). Risk of asthma was also affected by ethnic origin (highest for Western origin and lowest for north African origin, relative risk 1.63 (1.56 to 1.71)) and area of residence (highest in the central coastal region--risk of 1.24 (1.19 to 1.30) relative to the north coastal region--and lowest in inland areas--risk of 0.67 (0.64 to 0.70) relative to north coastal region).

CONCLUSIONS

Prevalence of asthma in Israel is increasing and is higher in males, in people of Western origin, and in those living in the most industrialised coastal region.

Factors affecting peak expiratory flow variability and bronchial reactivity in a random population sample

BACKGROUND

Bronchial reactivity measurements are widely used in epidemiological studies to provide an objective marker of asthma. There are, however, several potential advantages of measuring peak expiratory flow (PEF) variability instead, particularly in large studies. PEF variability and bronchial reactivity were compared in a population sample to assess the relationships of the two measurements to factors known to be associated with airways disease, and to compare their response rates.

METHODS

Subjects aged 18-65 were randomly selected from the electoral register of an administrative area in eastern England and randomised to attend either for a bronchial challenge test measuring the provocative dose of methacholine producing a 20% fall in FEV1 (PD20), or to measure PEF at two hourly intervals during waking hours for one week. Skin tests with common allergens were performed and a smoking history obtained. PEF variability was expressed as the amplitude % mean (highest - lowest x 100/mean).

RESULTS

A total of 273 subjects (69%) collected a PEF meter but a completed record sheet was returned by only 247 (62%); this was still significantly more than the 202 subjects (54%) who attended for and successfully completed a challenge test. Amplitude % mean was higher in women than in men (9.7% v 8.5%). In multiple regression analysis amplitude % mean increased significantly with age, mean skin weal diameter, and with current smoking. The odds of having a PD20 below 24.5 mumol increased with mean skin weal diameter and were greater in current smokers. Neither age nor sex had a significant effect on bronchial reactivity but there were significant interactions between age and the effects of both smoking and atopy.

CONCLUSIONS

The higher response rate associated with the use of PEF variability measurement, and the association with factors implicated in the pathogenesis of airways disease, suggest that PEF variability would be a useful measurement to employ in epidemiological studies.

Bronchial responsiveness to exercise in a random sample of 494 children and adolescents from Copenhagen

To investigate the bronchial response to exercise, we studied a random sample of 494 children and adolescents, aged 7-16 years, from Copenhagen. Exercise challenge consisted of steady running on a 10% sloping treadmill for 6 min in a climate chamber. Furthermore, in 464 subjects a histamine challenge test was also performed. Of the 494 subjects studied, 81 (16%) had at least 10% and 30 (6%) at least 15% reduction in FEV1 within 15 min after exercise. Twenty-nine (6%) subjects had bronchial hyperresponsiveness to both histamine and exercise, 48 (10%) subjects had bronchial hyperresponsiveness to exercise, but histamine responsiveness within the normal range, whereas 340 (73%) subjects had neither bronchial hyperresponsiveness to exercise nor inhaled histamine. With regard to the presence of asthma defined as substantial exercise induced bronchoconstriction (delta-FEV1 greater than or equal to 10%), exercise testing may not be appropriate for identifying clinical asthma in a random sample, because the highest predictive value of a positive test was 25%. On the other hand, a history of clinical asthma was frequently associated with increased bronchial responsiveness to exercise (77%). In conclusion, 16% of a random sample of children and adolescents had abnormal bronchial responsiveness to exercise (delta FEV1 greater than or equal to 10%), 6% of the subjects had a delta FEV1 greater than or equal to 15%. Furthermore, because of a low predictive value of a positive test, the exercise challenge test has only a supplementary role in the detection of clinical asthma in population samples.

Asthma morbidity in Australia: an epidemiological study

OBJECTIVE

To examine the prevalence and management of asthma in adults and children in a population sample in eastern Australia.

SETTING

A random sample of children from 33 primary schools in Sydney, Melbourne, Brisbane, and the Upper Hunter Valley (New South Wales), and their parents.

DESIGN

A cross-sectional analytic survey of 8753 primary school children aged between 5 and 12 years, and their parents (n = 13,945 adults). Asthma prevalence and management practices were determined by parental responses to a questionnaire, and spirometry was performed in children with "probable asthma".

RESULTS

Of 8753 children whose parents responded, the prevalence of current wheeze was 19.5% and diagnosed asthma was 17.1%. Of the children with "probable asthma", 30% had their lung function measured in the previous year, and 6% possessed both a peak flow meter and an action plan for their asthma. Undertreatment was likely, as preventive asthma medications (inhaled corticosteroids or sodium cromoglycate) were used regularly by only 25.5% of these children and by 44.3% of children who had asthma symptoms more than twice per week. Children with the diagnosis of asthma reported higher rates of preventive medication use and ventilatory function measurement than children with frequent symptoms without the diagnosis. In the 13,945 adults, the reported prevalence of asthma was 7%, of whom 39% were using preventive medications, 34% had their ventilatory function assessed in the previous year, and 7% had both a peak flow meter and an asthma action plan.

CONCLUSIONS

The study illustrated the gap between the current level of asthma management in the community and the standards set by the Thoracic Society of Australia and New Zealand. Undertreatment and suboptimal management of asthma remain important problems in Australia.

Asthma under-recognition and under-treatment in an Australian community

In a study in south-western Sydney, we examined asthma symptoms in a random sample of 4239 schoolchildren aged five-12 years. The prevalence of current wheeze and cough was 17.1% (95% CI 16.0-18.2%). Interviews were conducted with the parents of all 214 symptomatic children from two of the six schools. Only 60% of these children had ever been labelled as asthma, and only 20% were using appropriate asthma treatment. Fewer than 6% had ever had their airway function assessed. There was a socio-economic difference, with better levels of asthma recognition and management in children attending the school in the more affluent region. The findings suggest that asthma recognition, assessment and management in the Australian community, as in New Zealand and the UK, may need to be improved.

Prevalence of asthma among 12 year old children in New Zealand and South Wales: a comparative survey

A survey of 12 year old schoolchildren was carried out in New Zealand and South Wales, the same questionnaire and exercise provocation test being used. The prevalence of a history of asthma at any time was higher in New Zealand (147/873, 17%) than in South Wales (116/965, 12%). The New Zealand children were also more likely than the Welsh children to have a history of "wheeze ever" (27% versus 22%), and wheeze brought on by running (15% versus 10.5%). The sex ratio of asthmatic and wheezy children was very similar in the two countries. A history of hospital admission for chest trouble was twice as common in New Zealand as in South Wales. An exercise test produced a fall in peak expiratory flow rate of 15% or more in more New Zealand children (12.2%) than Welsh children (7.7%). These results suggest that the prevalence of childhood asthma is higher in New Zealand than in South Wales.

Racial inequalities in childhood asthma

Mortality and hospital admission rates for asthma are higher in Maoris and Pacific Islander children than in European children. These ethnic differences are not explained by ethnic differences in asthma prevalence, the characteristics of the disease or admission criteria. There are major ethnic differences in asthma drug management both in the community and at the time of discharge from hospital. In particular Polynesians were less likely to receive prophylactic therapy and this factor probably accounts for ethnic differences in mortality and admission rates. Possible explanations for the ethnic differences in medical management are discussed.

The interrelationship among bronchial hyperresponsiveness, the diagnosis of asthma, and asthma symptoms

Bronchial hyperresponsiveness (BHR) to inhaled histamine has often been cited as the gold standard in asthma diagnosis, but recently this has been questioned. This report assesses the relationship of BHR to asthma symptoms and asthma diagnosis in a large community-based sample of children. A total of 2,053 children 7 to 10 yr of age were randomly sampled from Auckland primary schools and assessed by a questionnaire and histamine inhalation challenge. In all, 14.3% had had asthma diagnosed, 29.6% reported having had one of the four respiratory symptoms in in the previous 12 months, and 15.9% had BHR (PD20 less than or equal to 7.8 mumol histamine). After a cumulative dose of 3.9 mumol histamine, the percent change in FEV1 from postsaline FEV1 was unimodally distributed, with those in whom asthma had been diagnosed dominating the severe end of the spectrum. However, 53% of those with BHR had no asthma diagnosis, and 41% had no current asthma symptoms. On the other hand, 48% of all subjects with diagnosed asthma and 42% of children with diagnosed asthma and current symptoms did not have BHR. Although severity of BHR tended to increase with wheezing frequency, all grades of severity (including no BHR) were found for any given frequency of wheeze. An existing diagnosis of asthma identified symptomatic children more accurately than did BHR, regardless of the criteria used for BHR or for "symptomatic" and irrespective of ethnic group. In conclusion, BHR is related to, but not identical to, clinical asthma. Bronchial challenge testing is an important tool of respiratory research, but cannot reliably or precisely separate asthmatics from nonasthmatics in the general community.