International Study of Asthma and Allergies in Childhood (ISAAC): rationale and methods

Pulmonary function in children with initial low birth weight

The objective of this analysis was to examine the effect of low birth weight and prematurity on bronchial air-flow, bronchial reactivity, airway symptoms and asthma diagnosis at school age. A cross-sectional epidemiological study was performed in three small towns in the eastern part of Germany on 2470 school children aged 5-14 (89.1% of eligible children). A 78 item questionnaire to determine risk factors at birth and in early childhood was employed. 7.8% of the children were born before completing 38 gestational weeks; 6.6% had a birth weight less than 2500 g. Pulmonary function analysis were done by a mobile plethysmography at the school. There were only weak restrictions in lung volume in term low birth weight (LBW) children (100 ml lower TLC, p = 0.107), and flow (257 ml lower PEFR, p = 0.108), were low. However, bronchial hyper-responsiveness indicated by 292 ml lower FEV1.0 after cold air bronchial provocation, was significantly increased compared to term normal birth weight children (p < 0.001). The effect of LBW was less in older children, only slightly stronger in girls and increased in children mechanically ventilated during the postnatal period. Correspondingly, there was a higher prevalence of diagnosed asthma in term LBW children (OR 1.6, 95%-confidence interval 1.0-2.6), however these were without an increased risk for any allergic sensitization. LBW, therefore, seems to be a risk factor for smaller lungs and hyperreactive airways primarily in term born children, whereas in preterm children the immature bronchial system seems to be recover by school age.

Pediatric reference values for respiratory resistance measured by forced oscillation

OBJECTIVES

To determine, in North American children, reference values for respiratory resistance measurements by the forced oscillation (Rfo) technique and to examine whether sitting height, as index of truncal length, is a better determinant of resistance, less influenced by race and gender, than standing height.

DESIGN/SETTING

A prospective cross-sectional study of healthy nonobese children, carefully selected for absence of atopy, exposure to tobacco smoke, and recent upper respiratory tract infection.

MEASUREMENTS

Three measurements of respiratory resistance by forced oscillation were obtained at the fixed frequencies of 8 Hz (Rfo8), 12 Hz (Rfo12), and at 16 Hz (Rfo16) using the Custo Vit R (Custo Med GMBH; Munich, Germany). In cooperative children, routine spirometry (FEV1, FVC, and peak expiratory flow rate [PEFR]) was also performed.

RESULTS

We recruited 217 healthy children aged 3 to 17 years. Reproducible measurements of Rfo8 were obtained for 206 children, Rfo12 for 197 children, and Rfo16 for 209 children. Normal FEV1, FVC, and PEFR values were documented in all 69 subjects who were able to reproducibly cooperate with spirometry. Multiple linear regression identified measurements of either sitting or standing height as the best, and equally strong, determinants of respiratory resistance at all three frequencies. Gender and race were not important factors once either sitting or standing height measurement was considered. Our regression equations at 8 Hz are comparable to published reference values obtained at fixed frequencies of 6, 8, and 10 Hz using other instruments. However, in comparison to our results, prior values tended to underestimate resistance in the shortest children or to overestimate it in the tallest ones. Our regression equation for Rfo12 is similar to the only previously published one, while no reference values at 16 Hz were available for comparison.

CONCLUSIONS

Height is the best predictor for total respiratory resistance at 8, 12, and 16 Hz in children aged > or = 3 years. Use of sitting height does not appear to be a stronger determinant of resistance than standing height.

Comparison of responses to an asthma symptom questionnaire (ISAAC core questions) completed by adolescents and their parents. SCARPOL-Team. Swiss Study on Childhood Allergy and Respiratory Symptoms with respect to Air Pollution

The primary objective of the study was to determine the impact of the identity of the respondent (parents versus adolescents) on prevalence estimates of asthma symptoms in Swiss adolescents. In addition, factors influencing agreement between parents' and adolescents' responses to the same questions were analysed. One thousand three hundred and seventy-four (78.4%) adolescents, aged 14 years, self-completed a questionnaire at school based on the International Study of Asthma and Allergy in Childhood (ISAAC) core questions on wheezing and asthma. The same questions were incorporated into a questionnaire to be completed by the parents at home. The adolescents' self-reported prevalence rates of current asthma symptoms and "asthma ever" were significantly higher than those obtained from the parental questionnaires. 856 (62.6%) parental questionnaires were filled in by parents without the help of the adolescents, 460 (37.4%) were completed by parents and adolescents and 51 (3.7%) were completed by the adolescents without the parents. Prevalence rates were higher when parents and adolescents completed the questionnaire jointly than when questionnaires were completed by parents alone. The level of agreement between parental and self-completed questionnaires was moderate to low (kappa coefficients 0.22-0.68). Agreement between parental and adolescents reports of asthma symptoms was best when questionnaires were completed jointly by parents and adolescents, when the adolescent was a girl, when a family history of asthma was recorded, when the adolescent was a non-smoker, and when the parental education was high. We conclude that the higher reporting of prevalence rates of current asthma symptoms by adolescents compared to reporting by their parents demonstrates the need to take the respondent to a questionnaire into account when comparisons are made between prevalence studies. The results also suggest that factors related to the family milieu influence symptom reporting.

Treatment of childhood asthma. Options and rationale for inhaled therapy

Epidemiological studies suggest the prevalence of asthma is increasing, though some remain sceptical as to the magnitude or indeed the presence of an increase. However, despite improved diagnosis and the availability of the potent drugs now available there remains considerable respiratory morbidity associated with asthma. It is clear from a number of studies that failure to deliver drugs to the lungs when using inhaler devices is a factor contributing to this high level of morbidity. Failure of drug delivery may result from the prescribing of inappropriate devices, failure to use devices appropriately or failure to comply with a treatment regimen. For most of the currently available forms of asthma therapy there are significant advantages to be gained from administering them in aerosol form. The benefits to be derived from administering these drugs as an aerosol include a rapid onset of action for drugs such as beta-agonists and a low incidence of systemic effects from drugs such as beta-agonists and corticosteroids. Over the past 25 years our understanding of the nature of asthma has changed. Though this has been reflected in the emphasis on inhaled corticosteroid therapy in recent guidelines, it has not been reflected in the range of inhaler devices available. Manufacturers continue to place drugs such as corticosteroids in the same devices as short acting beta-agonists even though the requirements for these different drug classes are very different. It is likely that this contributes to suboptimal therapeutic responses with inhaled corticosteroids. However, the variability associated with current delivery systems is relatively small compared with the variability introduced by poor compliance. There is no work currently available to indicate how the use of cheap disposable devises which do not incorporate any form of positive feedback influence compliance with inhaled steroids. Optimising aerosolised drug delivery in childhood involves consideration of the class of drugs, the particular drug within a class but more importantly, the age and abilities of the child. Devices must be selected to suit a particular child's needs and abilities. Devices utilising tidal breathing are generally used such as spacing chambers or, less commonly these days, nebulisers. A screaming or struggling child, or failure to use a closely fitting mask, reduces drug delivery to the lungs enormously. Failure to respond to inhaled therapy in early childhood may be attributable to failure of drug delivery. Drug delivery in early childhood using current devices remains more an art than a science.

Pulmonary function, exercise performance, and growth in survivors of congenital diaphragmatic hernia

A cohort of survivors of congenital diaphragmatic hernia (CDH), with matched controls, was studied to assess growth, respiratory function, and exercise performance. Nineteen of 24 survivors from an 11 year period (79%) were compared with 19 matched controls. Subjects had detailed auxology, performed spirometry and cycle ergometry, and completed questionnaires about respiratory symptoms and exercise. There were no significant differences between the groups for height, weight, sitting height, head circumference, or body mass index expressed as SD scores. The mean (95% confidence interval) percentage predicted forced vital capacity (FVC) was 84.7% (79.1 to 90.3) in index cases and 96.5% (91.4 to 101.6) in controls (p < 0.01). There was no significant difference in total lung capacity. Expiratory flow rates corrected for FVC were also similar between groups, suggesting normal airway function relative to lung size. Mean maximum oxygen consumption in ml/kg/min was 40.1 (36.8 to 43.4) and 42.2 (38.5 to 45.8) in index and control cases. These differences were not significant. Index cases achieved a similar minute ventilation to controls by more rapid and shallower breathing. Index cases had lower perception of their own fitness and lower enjoyment of exercise, although habitual activity levels were similar. Survivors of CDH repair have reduced functional lung volumes, but normal airway function compared with matched controls. They have no growth impairment nor significant impairment of exercise performance, although they have more negative perceptions of their own fitness. They should be encouraged and expected to participate fully in sport and exercise.

Asthma, type-1 allergy and related conditions in 7- and 8-year-old children in northern Sweden: prevalence rates and risk factor pattern

As a first step in an intervention study of asthma and allergic diseases among school children, a cross-sectional study was performed during Winter 1996 in three towns (Kiruna, Luleå and Piteå) in the northernmost province of Sweden, Norrbotten. The cross-sectional study aimed to measure the prevalence of asthma, type-1 allergy and allergic diseases in order to make it possible to measure the incidence of the diseases, conditions and symptoms related to the diseases. Another aim was to perform a screening for possible risk factors. All children enrolled in the first and second classes at school, 7 and 8 years old, were invited to take part in this study. The ISAAC questionnaire with added questions about symptoms, morbidity, heredity and environment was distributed by the schools to the parents. The response rate was 97%, and 3431 completed questionnaires were returned. The children in two of the municipalities were also invited to skin test, and 2149 (88%) were tested with 10 common airborne allergens. The results showed that 7% of the children were currently using or had used asthma medicines during the last 12 months. Six percent had asthma diagnosed by a physician, and 4% were using inhaled corticosteroids. The prevalence of wheezing during the last 12 months was 12%, rhinitis without colds 14%, and eczema 27%, while 21% had a positive skin test. The respiratory symptoms and conditions were significantly greater in boys and, further, they were most prevalent in Kiruna in the very north, though not significantly. Type-1 allergy and asthma had different risk factor patterns. The main risk factors for asthma were a family history of asthma (OR = 3.2) followed by past or present house dampness (OR = 1.9), male sex (OR = 1.7) and a smoking mother (OR = 1.6). In Kiruna, when none of these three risk factors were present, none of the children had asthma, but when all three were present, 38% of these children were using asthma medicines.

The physical activity level in children with asthma based on a survey among 7-16 year old school children

The objective was to compare the physical activity level of children with asthma with that of non-asthmatic children. A standardized written questionnaire was administered in a survey of school children in three different areas of Norway: Oslo (n = 2577), Hallingdal (n = 831) and Odda (n = 1177). Response rates were > 85% in all areas, and approximately 50% of the respondents were female. No significant differences were found between the distributions in exercise frequency either for children reported ever to have had asthma (P = 0.8) or for those with current asthma (P = 0.3) compared to non-asthmatics. Similar results were found for exercise hours a week. More than 50% of all children took part in organized sport. The data suggest that asthmatic children are as physically active as their peers.

Health effects of passive smoking. 3. Parental smoking and prevalence of respiratory symptoms and asthma in school age children

BACKGROUND

A systematic quantitative review of the evidence relating parental smoking to the prevalence of asthma and respiratory symptoms was conducted amongst school age children.

METHODS

Sixty relevant studies were identified after consideration of 1593 articles selected by electronic search of the Embase and Medline databases using keywords relevant to passive smoking in children. The search was completed in April 1997 and identified 25 studies of asthma, 41 of wheeze, 34 of chronic cough, seven of chronic phlegm and six of breathlessness which were included in a quantitative overview.

RESULTS

The pooled odds ratios for either parent smoking were 1.21 (95% CI 1.10 to 1.34) for asthma, 1.24 (95% CI 1.17 to 1.31) for wheeze, 1.40 (95% CI 1.27 to 1.53) for cough, 1.35 (95% CI 1.13 to 1.62) for phlegm, and 1.31 (95% CI 1.08 to 1.59) for breathlessness. Adjustment for confounding had little effect. Evidence of heterogeneity between studies appeared largely explicable by publication bias with a superfluity of small studies with large odds ratios. However, excluding these had little effect on the pooled odds ratios. The prevalence of all symptoms increased with the number of parents who smoked. While maternal smoking had a greater effect than paternal smoking, the effect of father only was clearly significant.

CONCLUSIONS

The relationship between parental smoking and respiratory symptoms seems very likely to be causal given statistical significance, robustness to adjustment for confounding factors, consistency of the findings in different countries, and evidence of dose response. The raised risk in households where the father, but not the mother, smoked argues for a postnatal effect.

Social deprivation and asthma

This study was conducted to see whether children living in socially deprived areas were more likely than other children to be admitted to hospital for asthma, and, if so, whether their excess risk was attributable to a higher prevalence of asthma or poorer treatment. Hospital admission rates for asthma were obtained for Cardiff electoral wards and compared with the Townsend indices of deprivation. A survey of respiratory symptoms was conducted in schoolchildren; prevalence of symptoms was compared with Townsend index and asthma admission rate for the schools' catchment areas. Asthma admissions were strongly correlated with Townsend indices at all ages. The prevalence of reported asthma and various degrees of wheeze in the schools was not significantly correlated with Townsend index or hospital admission rate in the corresponding areas. The presence of a smoker in the house was strongly associated with Townsend index and admission rate; children whose houses contained a smoker were more likely than others to have wheezed in the past year and to have disturbed nights due to wheezing. There was a non-significant negative association between Townsend index and regular use of inhaled steroids. The relationship between hospital admission for asthma and social deprivation is not explained by variations in prevalence, but it may be attributable to the aggravation of symptoms by active or passive smoking, and perhaps also to differences in management.

Determinants of house dust mite allergen in homes in Wellington, New Zealand

OBJECTIVES

To measure levels of the major Dermatophagoidespteronyssinus allergen (Der p 1) in homes in Wellington, New Zealand, and to examine factors which affect these levels.

METHODS

As part of a study of risk factors for asthma among 474 8-10-year-old children, standard procedures were used to collect reservoir dust and to measure Der p 1 levels on the living room floor and child's bedroom floor and bedding. Der p 1 levels were analysed both as geometric mean microg/g of fine dust and as microg/m2. Questionnaires collected information about factors which might influence these levels, and an average relative humidity in the bed and on the bedroom floor was also measured.

RESULTS

Similar geometric mean levels of Der p 1 were found at each floor site - 25.5 microg/g (95% CI: 22.8-28.5) in the living room and 26.4 microg/g (95% CI: 23.7-29.3) on the child's bedroom floor. The geometric mean level of Der p 1 in the child's bed was 46.6 microg/g (95% CI: 42.3-51.3). After controlling for possible confounders, geometric mean living room and bedroom floor Der p 1 levels were significantly higher in households with older carpet than households with no carpets or newer carpets, and higher in the autumn. Households with three or more children had higher levels of Der p 1 than households with fewer children. Bedding levels were significantly higher in beds with kapok or inner sprung mattresses, or wool underlays and at relative humidities above the mean (51%).

CONCLUSION

The very high levels of house dust mite allergen (Der p 1) found in Wellington are likely to be due to a variety of life-style and climatic factors. However, the type and age of floor covering appears to be the single most important factor.

Reduced forced expiratory flow in schoolchildren with respiratory symptoms: the Odense Schoolchild Study

In the present population-based study, spirometric lung function was assessed in symptomatic schoolchildren with and without asthma as compared to an asymptomatic reference group. The primary aim was to investigate if impaired lung function could be demonstrated in symptomatic schoolchildren, even in the absence of diagnosed asthma. Spirometry [forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), 50% of forced expiratory flow (FEF 50%) and 75% of forced expiratory flow (FEF 75%)] and anthropometric measures (standing height, weight, skin fold thickness, and length and circumference of the upper arm) were obtained from 1369 8-10-year-old children (81.5% of the eligible population) during the school year 1985-86. In 1321 of those subjects (96.5% of those examined), a self-administered questionnaire was completed. Thirty-five children belonging to ethnic minorities were excluded, thus 1286 subjects were included for further analysis. Point prevalences concerning asthma and respiratory symptoms (wheeze, cough and shortness of breath) were obtained. Thirty-seven children reported asthma and one or more asthma-like symptoms (symptomatic asthmatics), whereas 40 children denied having asthma, although claiming one or more asthma-like symptoms (symptomatic non-asthmatics). In both symptomatic groups, FEF 50% and FEF 75% were reduced relative to the reference group, the deficit being larger in the symptomatic asthmatics. FEF 75% was found to be more reduced than FEF 50%. FEV1 and FVC did not differ significantly between groups. It is concluded that only half of the schoolchildren with respiratory symptoms usually associated with the presence of asthma actually reported having this disease. These results demonstrate the presence of reduced lung function in symptomatic, reportedly non-asthmatic, children, suggesting clinically important underdiagnosis of asthma. More severe impairment of lung function was found in known asthmatics, also implying some degree of undertreatment.

Randomised controlled trial of inhaled corticosteroids (fluticasone propionate) in cystic fibrosis

BACKGROUND

Controlling lung inflammation may be the key to improving morbidity and mortality in cystic fibrosis.

OBJECTIVE

To assess the effects of inhaled corticosteroids on lung inflammation in cystic fibrosis.

DESIGN

Double blind placebo controlled randomised sequence crossover trial. Fluticasone propionate (400 micrograms/day) was given as a dry powder inhaler for six weeks with a four week washout period before crossover.

OUTCOME MEASURES

Sputum inflammatory markers (interleukin-8, tumour necrosis factor-alpha (TNF-alpha) and neutrophil elastase-both free and bound to alpha 1-antiprotease), sputum interleukin-10, lung function, and symptomatology.

SUBJECTS

Twenty three children from a regional cystic fibrosis centre were enrolled into the study, with mean age 10.3 years (range 7 to 17 years) and mean baseline forced expiratory volume in one second (FEV1) of 64% (range 21% to 102%) predicted for sex and height. One patient was excluded for non-compliance to the study protocol.

RESULTS

No significant benefit was shown for the use of fluticasone propionate in any of the outcomes. For sputum interleukin-8 there was an estimated true treatment median difference of 142 pg/ml (95% confidence interval (CI) 8 to 2866 pg/ml) in favour of placebo; while for maximal expiratory flow at 25% (MEF25%) remaining forced vital capacity predicted for sex and height there was a 15 percentage points (pp) (95% CI 4 to 26 pp) mean treatment difference in favour of placebo. Sputum interleukin-10 was undetected in any samples and unaffected by fluticasone propionate. Neither atopic status, baseline FEV1, nor concomitant DNase therapy had any effect on response to treatment.

CONCLUSIONS

Lack of benefit from fluticasone propionate was most likely due to failure of the drug to penetrate the viscid mucus lining the airways. It is suggested a large multicentre trial with higher doses given for a longer time by a different delivery system is required to assess efficacy.

Prevalence of asthma, rhinitis and eczema among schoolchildren in Kelantan, Malaysia

The prevalence and severity of asthma, rhinitis and eczema in Kelantanese schoolchildren were determined as part of an international study of the epidemiology of asthma and allergic diseases. The international study of asthma and allergies in childhood (ISAAC) written questionnaire was administered to 7055 schoolchildren from February 1995 to August 1995. The respondents were parents or guardians of 5- to 7-year-old children (n = 3939), and schoolchildren aged 12-14 years (n = 3116). The ISAAC video questionnaire (AVQ3.0) was shown to children aged 12-14 years after the written questionnaire. The overall prevalences of 'ever wheezed' and 'wheezing in last 12 months' were 9.4 and 6.0% respectively. The prevalence of 'ever diagnosed with asthma' was 9.4%. Both 'ever wheezed' and 'wheezing in the last 12 months' were significantly higher in 12- to 14-year-old children than in 5- to 7-year-old children, with P values of 0.0006 and 0.014 respectively. No gender differences in the prevalences were observed. For the complete study group, 4.7% of children had sleep disturbed by wheezing but only 1.1% had a severe attack limiting speech in the preceding 12 months. Sleep disturbance was more common in the 12- to 14-year-old children than in 5- to 7-year-old children (P = 0.006). There was no difference between the age groups for severe attacks limiting speech. The overall prevalence of rhinitis and eczema symptoms were 27 and 12%, respectively. The prevalence of rhinitis in the 12-14 year age group (38.2%) was significantly higher (P < 0.0001) than in the 5-7 year age group (18.2%). The prevalence of eczema in the 5-7 year age group (13.7%) was significantly higher (P = < 0.0001) than in the 12-14 year age group (9.9%). These prevalence data are comparable with previous reports in Malaysian children, but are considerably lower than those reported for most developed countries.

Validation of a rhinitis symptom questionnaire (ISAAC core questions) in a population of Swiss school children visiting the school health services. SCARPOL-team. Swiss Study on Childhood Allergy and Respiratory Symptom with respect to Air Pollution and Climate. International Study of Asthma and Allergies in Childhood

The primary aim of the study was to assess the validity of the ISAAC core questions on rhinitis in a population of Swiss school children by comparing them to skin prick test results. Second, the positive predictive value in detecting atopy among children with rhinitis symptoms was determined. Third, agreement between parental reports of hay fever and rhinitis symptoms was evaluated, since earlier Swiss prevalence surveys had exclusively relied on reported hay fever.

MATERIAL AND METHODS

Two thousand nine hundred and fifty-four (81.2%) parents of 7, 10 and 14-year old children filled in an exhaustive questionnaire which included the ISAAC core questions on rhinitis. Two thousand one hundred and twenty children also underwent skin prick testing against six common aeroallergens (grass mixture, birch, mugwort, D. pteronyssinus, cat and dog dander). The analysis is restricted to children with both questionnaire data and skin prick test results.

RESULTS

Sensitization to any allergen was most strongly associated with reported hay fever (OR = 5.7, 95% CI 4.4-7.4), nose problems accompanied by itchy-watery eyes (OR = 4.4, 95% CI: 3.3-5.7), symptoms occurring only during pollen season (March through September) (OR = 4.9, 95% CI: 3.6-6.5) and a combination of these latter two symptoms (OR = 5.8, 95% CI: 4.1-8.1). The association was stronger for a sensitization to outdoor allergens than for indoor allergens. The specificity of the various questions was high, ranging from 77.5% to 97.6%, but the sensitivity was low (2.6% to 42.7%). The positive predictive value for atopy among children with symptoms was 63% for sneezing accompanied by itchy-watery eyes, 67% for symptoms occurring only during the pollen season and 70% for reported hay fever. However, agreement between reported rhinitis symptoms and hay fever was only moderate. About one third of the children with symptoms indicative of seasonal rhinitis did not report the label "hay fever".

CONCLUSIONS

We conclude from our analyses that the ISAAC core questions on rhinitis are highly specific and therefore useful in excluding atopy. In addition they have a high positive predictive value in detecting atopy among children with symptoms, but they are not helpful for detecting atopy in a general population of children (low sensitivity). To monitor time trends in the prevalence of allergic rhinitis in Switzerland, questions on rhinitis symptoms as well as on the diagnostic label "hay fever" have to be included in a questionnaire because they contain complementary information since under-diagnosis of allergic rhinitis is common.

Prevalence of childhood asthma in Istanbul, Turkey

In order to determine the asthma prevalence in 6-12-year-old schoolchildren in Istanbul, we issued 2350 questionnaires, according to ISAAC criteria, in six randomly selected city primary schools to be completed at home by parents. A total of 2232 of the questionnaires were completed, an overall response rate of 94.9%, and 2216 questionnaires were taken into consideration. The prevalence of asthma was found to be 9.8% and wheezing 15.1%. To investigate the effect of socioeconomic status on the prevalence of asthma, we evaluated the heating system at home, the place of residence, the educational levels of the mother and father, the number of people living in the house, the sharing of bedrooms, and the annual family income. In conclusion, the prevalence of childhood asthma was not affected by any of these factors. Atopic family history, food allergy, eczema, and frequent otitis media and sinusitis attacks were evaluated and found to be significant in asthma prevalence.

The prevalence of respiratory symptoms and asthma among school children in three different areas of Norway

The role of exposure to ambient air pollution has been a topic of interest as a potential risk factor for respiratory symptoms and asthma. We expected that the prevalence rates would vary in Norway between the capital, Oslo, the mountainous area Hallingdal and the industrial area Odda. Surveys were conducted in school children, aged 6-16 years, in; Oslo (n = 2577), Hallingdal (n = 1177) and Odda (n = 831). The parent-reported prevalence of wheeze in past year was almost similar in Oslo (13.1 (95% CI 11.7-14.5)) and Upper Hallingdal (14.2 (13.1-15.3)), but lower in Odda (9.0 (7.0-11.0)). The findings for severe respiratory symptoms were almost equal. The age patterns within each area differed. The risk of wheeze ever (p < 0.001) and wheeze in past year (p = 0.04) decreased with increasing age in Odda, while there was an increase in the risk of exercise induced wheeze in Oslo (p = 0.02) and Hallingdal (p < 0.001). The lifetime prevalence of asthma was lowest in Odda (5.4 (3.8-7.0)) compared to Oslo (9.4 (8.2-10.6)) and Hallingdal (8.5 (6.8-10.2)). There was a positive association between physical activity and wheeze in past year. The results do not support the hypothesis that respiratory morbidity is more common in urban than rural areas, age and physical activity can influence the prevalence rates of respiratory symptoms in school children.

Stability of respiratory symptoms in unlabelled wheezy illness and nocturnal cough

OBJECTIVE

To assess the natural history of respiratory symptoms not labelled as asthma in primary schoolchildren.

DESIGN

Repeat questionnaire survey of subgroups identified from a previous questionnaire survey after a two year delay.

SUBJECTS

The original population of 5321 Sheffield children aged 8-9 years yielded 4406 completed questionnaires in 1991(82.8%). After excluding children with a label of asthma, there were 370 children with current wheeze, 129 children with frequent nocturnal cough, and a random sample of 222 children with minor cough symptoms and 124 asymptomatic children.

RESULTS

Response rates in the four groups were 233 (63.0%), 77 (59.7%), 160 (72.1%), and 90 (72.6%) respectively. Of those who initially wheezed, 114 (48.9%) had stopped wheezing and 42 (18.0%) had been labelled as having asthma. Those with more frequent wheezing episodes (p < 0.02) and a personal history of hay fever (p < 0.01) in 1991 were more likely to retain their wheezy symptoms. In the children with frequent nocturnal cough in 1991, 20.1% had developed wheezing, 42.9% had a reduced frequency of nocturnal coughing, and 14.2% had stopped coughing altogether two years later. One sixth had been labelled as having asthma. Children with nocturnal cough were more likely to develop wheezing if they had a family history of atopy (p = 0.02). Only 3.8% and 3.3% of those with minimal cough and no symptoms respectively in 1991 had developed wheeze by 1993 (1.9% and 1.0% labelled as asthma).

CONCLUSIONS

Most unlabelled recurrent respiratory symptoms in 8-10 year olds tend to improve. Unlabelled children who have persistent symptoms have other features such as frequent wheezing attacks and a family or personal history of atopy. If a screening questionnaire were to be used to identify such children, a combination of questions should be employed.

Problems of measuring asthma prevalence

This review considers the issues involved in measuring the community prevalence of asthma, particularly in the context of international comparisons. We argue that there is no gold standard definition for measuring asthma prevalence, and discuss the currently available methods of case ascertainment. Prevalence studies, if they are to be generalizable, need to involve large sample sizes with high response rates. This necessitates methods that are simple, inexpensive and practicable, but also as sensitive and specific for asthma as possible. We discuss some of the issues that are specific to comparisons of asthma prevalence between diverse populations, and suggest that large surveys using written or video questionnaires of self reported symptoms validated in all of the target populations are the method of choice.

Interrelationships between diagnosed asthma, asthma-like symptoms, and abnormal airway behaviour in adolescence: the Odense Schoolchild Study

BACKGROUND

The diagnosis of asthma is based on several characteristics including symptoms and suitable tests of airway lability. However, it is neither clear to what degree various tests and symptoms identify the same subjects, nor how these characteristics are best combined to diagnose asthma. The interrelationships between physician-diagnosed asthma, asthma-like symptoms, and abnormal airway function, as defined by four commonly used tests, have therefore been assessed.

METHODS

A population based sample of 495 Danish schoolchildren aged 12-15 years, comprising 292 randomly selected subjects and 203 subjects considered at risk of having or developing asthma, was examined. Symptoms and background information were recorded by questionnaire. The test panel consisted of baseline forced expiratory volume in one second (FEV1%), provocation with treadmill exercise (EXE) and with inhaled methacholine (PD15), and monitoring of peak expiratory flow (PEF) twice daily for two weeks.

RESULTS

The sensitivity for diagnosed asthma was highest for PD15 followed by PEF monitoring, whereas specificity for asthma or asthma-like symptoms was marginally higher with the other two tests. Most symptomatic subjects with any positive test were identified by PD15 alone (75%) or in combination with PEF monitoring (89%). PEF variability was more susceptible to treatment with inhaled steroids than the PD15 index. Although inter-test agreement was weak (kappa < 0.40 for all pairs), significant associations were found between PD15 and EXE, PEF and EXE, and FEV1% and PD15.

CONCLUSIONS

The agreement between the four tests was weak. In particular, PEF variability and methacholine responsiveness seem to identify different varieties of airway pathophysiology. The combined use of methacholine provocation testing and PEF monitoring may be helpful as an epidemiological screening tool for asthma.

Longitudinal study of free running exercise challenge: reproducibility

The reproducibility of free running exercise challenge has been examined in an unselected population of 8-10 year olds. Using a standardised protocol, monthly exercise tests were performed on 143 children over one year. A positive test was defined using both a 15% and 20% fall in peak expiratory flow after exercise. The mean (95% confidence interval, CI) population frequency for a positive test at 15% fall was 14.9% (6.5 to 23.3) and coefficient of variation 24.6%. For a 20% fall, the mean (95% CI) population frequency was 7.9% (2.9 to 12.9) and coefficient of variation 27.8%. Seventy two (50.3%) of the children gave at least one positive response at 15% fall. Exercise testing is not reproducible in the community setting and should not be used as a screening test. Exercise data from epidemiological studies of asthma should be interpreted with caution.