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Keywords:

  • allergic rhinitis;
  • asthma;
  • cross-sectional study;
  • eczema;
  • ISAAC;
  • prevalence

Abstract

  1. Top of page
  2. Abstract
  3. Methods
  4. Population and data collection
  5. Outcome measures
  6. Data analysis
  7. Results
  8. Discussion
  9. Acknowledgments
  10. References

Objective: To assess time trends in symptoms of asthma, allergic rhinitis, and atopic eczema among children in Münster, Germany.

Methods: Two cross-sectional surveys 5-years apart (1994/1995, 1999/2000) using ISAAC core written and video questionnaires and applying the ISAAC protocol. Two main age groups (6–7 and 13–14 year olds) were designated with information collected by parental and self-report for both age groups, respectively. A school-based sample of 7744 participants in the 1994/1995 survey and 7962 participants in the 1999/2000 survey was recruited. In the first and second surveys, response rates for the 6–7 year olds were 81 and 82%, respectively, while for the 13–14 year olds response rates were 94% in both. Analyses focus on the change in 12-month prevalence of symptoms of asthma, rhinitis, and eczema.

Results: There is a tendency towards an increase in current symptoms for all three conditions and in both age groups, but more so among girls. Indices of diagnosis either remained the same or increased in parallel to the increase in symptoms. Indices of severity also showed a homogenous increase in the 5-year study period.

Conclusions: Our study shows that symptoms of asthma, rhinitis, and eczema are increasing, reflecting a change in the morbidity of these conditions in our population.

There is a wide consensus that asthma and allergies are witnessing a rising trend among children especially in western societies (1, 2). In some western countries asthma and allergies have reached alarming proportions, affecting up to one-third of children within the general population (3). Although most of the information about the increase in asthma and allergies come from studies on school children, recent evidence from the UK suggests that wheezing disorders, including viral wheeze, are increasing in preschool children as well, indicating a generalized trend (4). Asthma and allergies rank high on the public health agenda in many countries, highlighting the need for continuous monitoring and assessment of the dynamics of these disorders and factors that influence their trends (5). In Leipzig, Germany, surveys conducted between 1991 and 1996 showed a substantial increase in the prevalence of hay fever and atopic sensitization, but not asthma (6).

While there is general agreement on the increasing trends of asthma and allergies in western countries, a lot of factors can affect our assessment of those trends such as changes in severity, changes in medical care practices, and changes of diagnostic labelling of these disorders (7, 8). On the other hand, despite extensive research devoted to studying time trends in asthma and allergies, methodological problems, especially those related to comparability and generalizability of research results, still hinder the establishment of a reliable picture about the epidemiology of asthma and allergies worldwide (9, 10). Having such reliable data is instrumental for the generation of valid concepts about possible driving forces, intervention strategies, and for the assessment of costs of asthma and allergies within the society. A considerable amount of effort, therefore, has been devoted in the last decade or so to the development and refinement of standardized, sensitive, and practical survey tools that can be widely applied to measure the burden of, and factors associated with, these disorders in different populations and to allow for reliable assessment of disease trends spatially and secularly (9–11).

The International Study of Asthma and Allergies in Childhood (ISAAC) is one of the pioneer and most comprehensive efforts aiming at the creation of a reliable map on the international trends in asthma and allergies that will foster better understanding of their patterns as well as hint towards possible etiological factors (12, 13). It is in brief a three-phase multi-centre, multi-national project, with phases I and III involving the conduction of identical surveys at least 5 years apart to look at the spread and time trends in childhood asthma and allergies worldwide (12). To the best of our knowledge, this is the first study within the ISAAC framework to report the time trends in symptoms of asthma, allergic rhinitis, and atopic eczema based on data collected from Phase I (1994/1995) and Phase III (1999/2000) in Münster, Germany.

Population and data collection

  1. Top of page
  2. Abstract
  3. Methods
  4. Population and data collection
  5. Outcome measures
  6. Data analysis
  7. Results
  8. Discussion
  9. Acknowledgments
  10. References

Methods of the international ISAAC and ISAAC Münster projects have been described in detail elsewhere (14, 15). Briefly, this study uses the information collected on two occasions 5 years apart (Phase I 1994/1995, Phase III 1999/2000), using identical methods on symptoms of asthma and allergies in two age groups referred to as 6–7 year olds and 13–14 year olds. A random sample of all schools in the city of Münster was selected, and all pupils in the two grades with the highest proportion of 6–7 and 13–14 year olds were approached. The number of schools participating in the two surveys was 90 and 91 in 1994/1995 and 1999/2000, respectively. The overall number of participants in the first survey was 7744 (3741 in the 6–7-year age group, 4003 in the 13–14-year age group) with response rates of 81 and 94%, for both age groups, respectively, while the overall number of participants in the second survey was 7962 (3830 in the 6–7-year age group, 4132 in the 13–14-year age group) with response rates of 82 and 94%, for both age groups, respectively. Information for the younger age group was collected by parental report, while for the older age group it was collected by self-report (14). Questionnaires used in both groups contained the ISAAC core questions on symptoms of asthma and allergies. During the design period of the ISAAC project, the German version of these questions was piloted and validated among schoolchildren in the city of Bochum (16). In both surveys, information was collected outside the main pollen season and within the same time of the year (August–January).

As recommended by the ISAAC protocol, we used for the 13–14-year-old age group the video questionnaire, which showed five sequences related to asthma symptoms and severity: (i) moderate wheezing at rest; (ii) wheezing and shortness of breath after exercise; (iii) nocturnal wheezing; (iv) nocturnal cough; and (v) severe wheezing and shortness of breath at rest (17, 18). For the two surveys, the Caucasian version of the video questionnaire was used after the written one, whereby participants answered specific questions after viewing each sequence (15, 17, 18).

Outcome measures

  1. Top of page
  2. Abstract
  3. Methods
  4. Population and data collection
  5. Outcome measures
  6. Data analysis
  7. Results
  8. Discussion
  9. Acknowledgments
  10. References

Main outcome measures used in this study were 12-month prevalence of symptoms of asthma (current wheeze), allergic rhinitis (current rhinitis), and atopic eczema (current eczema). According to ISAAC phase I and III main modules and consistent with previously published reports from the ISAAC project, these outcome measures were obtained from core questions about the presence of wheezing or whistling in the chest in the past 12 months (17–19), about having a problem with sneezing, or a runny/blocked nose when the participant did not have a cold or flu in the past 12 months (20), and about the presence of an itchy rash in the last 12 months that affected the skin creases (21). To cover as much as possible the range of presenting symptomatology of childhood asthma, we included in the analyses responses to questions about the presence of exercise-induced wheeze, and about dry cough at night not due to cold or chest infection (14, 17, 18). Information related to lifetime diagnosis of the three disorders were obtained from answers to three questions about ever having had asthma, hay fever, or eczema (14, 17, 18). For the 13–14 year olds, responses to the five video sequences related to 12-month prevalence and severity of asthma symptoms are included in the current analyses.

Severity of asthma symptoms was assessed among children with current wheeze from responses to questions about the number of wheezing attacks in the last 12 months, about sleep disturbance due to wheezing, and about the presence of speech-limiting wheeze in the last 12 months (14, 17, 18). Severity of allergic rhinitis was assessed among children with current rhinitis from the responses to the questions on the presence of accompanying itchy-watery eyes, and about interference with daily activities because of the nose problem. Finally, severity of atopic eczema was assessed based on the response to a question about interference with sleeping because of the itchy rash (14, 17, 18). Consistent with an earlier report from Münster, severity indices were subcategorized into (none) and (any) (15).

Data analysis

  1. Top of page
  2. Abstract
  3. Methods
  4. Population and data collection
  5. Outcome measures
  6. Data analysis
  7. Results
  8. Discussion
  9. Acknowledgments
  10. References

Of the 15 706 total participants (phases I and III combined), 128 (0.81%) had missing values for sex or nationality, and could not be included in the analyses. To be able to assess time trends of symptoms of asthma and allergies in a rather homogenous population we opted to restrict our analyses to children with known German nationality. Accordingly, 1009 (6.42%) non-Germans were excluded from the analyses, leaving a total of 14 569 participants for subsequent analyses. A gender/age stratified description of the study participants is found in Table 1. Missing or inconsistent responses were included in the denominator for calculation of prevalence figures while they were excluded from subsequent bivariate analyses in accordance with ISAAC recommendations (19–22). Our prevalence estimates, therefore, are conservative; they are calculated by dividing positive responses to the given question by the total number of completed questionnaires for the corresponding stratum. Analyses were done using SAS 8.02 statistical package. Chi-square (χ2) tests were done to test for statistical significance in comparisons of proportions between the two surveys, and prevalence odds ratios (POR) and 95% confidence intervals (95% CI) were calculated. To test whether the difference between odds ratios for time trends of different severity levels is significant, a test of homogeneity of the odds ratios was calculated and a resulting P value <0.05 was considered significant.

Table 1.  Descriptive statistics of the study population*
 1994/1995 survey (phase I)1999/2000 survey (phase III)
N (%)Mean age ± SDN (%)Mean age ± SD
  1. * German nationals with known sex.

6–7-year age group
 Male1754 (50.6)6.90 ± 0.781863 (52.8)6.85 ± 0.76
 Female1713 (49.4)6.87 ± 0.761666 (47.2)6.84 ± 0.73
 Total3467 (100)6.88 ± 0.773529 (100)6.84 ± 0.75
13–14-year age group
 Male1865 (49.6)13.43 ± 0.931894 (49.6)13.34 ± 0.84
 Female1892 (50.4)13.28 ± 0.891922 (50.4)13.24 ± 0.94
 Total3757 (100)13.35 ± 0.913816 (100)13.29 ± 0.94

Results

  1. Top of page
  2. Abstract
  3. Methods
  4. Population and data collection
  5. Outcome measures
  6. Data analysis
  7. Results
  8. Discussion
  9. Acknowledgments
  10. References

Apart from eczema among 13–14-year-old boys, there was a general increase in current symptoms for all three conditions and in both age groups (Tables 2 and 3). The increase was generally more marked among girls compared to boys for all three conditions and in both age groups (Fig. 1A,B). Indices of severity also showed a general increase in the 5-year study period, with the increase being generally homogenous across all severity levels (Tables 2 and 3). For the 13–14 year olds, responses to the video sequences about 12-month prevalence of symptoms of asthma showed similar time trends as was observed from the written questionnaires, although on a smaller scale (Table 4). The test of homogeneity of odds ratios was statistically significant only in two subgroups, indicating a greater increase in the higher severity category (any vs none, Table 3). In the younger age group, indices related to lifetime diagnosis (ever asthma, ever hay fever, ever eczema) either remained the same or increased to a lower extent than indices related to current symptoms (Table 2), while in the older age group indices of medical diagnosis either increased in parallel to the increase in symptoms (asthma, rhinitis) or surpassed the increase in symptoms (eczema) (Table 3).

Table 2.  Time trends of symptoms, severity, and diagnosis of asthma, allergic rhinitis, and atopic eczema among 6–7 year olds* in Münster
 BoysGirls
1994/1995 survey (N = 1754)1999/2000 survey (N = 1863)POR** (95% CI)1994/1995 survey (N = 1713)1999/2000 survey (N = 1666)POR (95% CI)
n (%)n (%)n (%)n (%)
  1. * Parental report. ** Prevalence odds ratio.

12-Month prevalence of asthma symptoms
Wheeze210 (12.0)254 (13.6)1.2 (0.95–1.41)128 (7.5) 212 (12.7)1.8 (1.42–2.28)
Night cough263 (15.0)303 (16.3)1.1 (0.91–1.31)223 (13.0)257 (15.4)1.2 (0.99–1.48)
Exercise-induced wheeze132 (7.5) 146 (7.8) 1.0 (0.80–1.32)81 (4.7)100 (6.0) 1.3 (0.93–1.73)
Number of wheeze attacks
 None38 (2.2)40 (2.1)1.0 (0.62–1.59)17 (1.0)31 (1.9)1.9 (1.01–3.57)
 Any167 (9.5) 211 (11.3)1.2 (0.97–1.51)105 (6.1) 179 (10.7)1.8 (1.42–2.38)
Speech-limiting wheeze
 None150 (8.6) 197 (10.6)1.3 (1.0–1.59)111 (6.5) 180 (10.8)1.8 (1.35–2.25)
 Any55 (3.1)54 (2.9) 0.9 (0.62–1.37)14 (0.8)31 (1.9)2.3 (1.17–4.55)
Sleep disturbance due to wheeze
 None90 (5.1)116 (6.2) 1.2 (0.91–1.64)52 (3.0)85 (5.1)1.7 (1.19–2.47)
 Any111 (6.3) 133 (7.1) 1.1 (0.87–1.49)69 (4.0)123 (7.4) 1.9 (1.39–2.60)
Lifetime diagnosis
Asthma ever86 (4.9)96 (5.2)1.1 (0.77–1.42)46 (2.7)60 (3.6)1.4 (0.90–2.03)
12-Month prevalence of rhinitis symptoms
Rhinitis272 (15.5)337 (18.1)1.2 (1.01–1.44)165 (9.6) 241 (14.5)1.6 (1.29–1.98)
Rhino-conjunctivitis130 (7.4) 150 (8.0) 1.1 (0.85–1.41)66 (3.9)98 (5.9)1.6 (1.12–2.17)
Interference with daily activities
 None94 (5.4)135 (7.2) 1.4 (1.05–1.83)65 (3.8)108 (6.5) 1.8 (1.26–2.43)
 Any174 (9.9) 193 (10.4)1.1 (0.84–1.31)92 (5.4)130 (7.8) 1.5 (1.12–1.98)
Lifetime diagnosis
Hay fever ever123 (7.0) 137 (7.4) 1.1 (0.81–1.36)71 (4.1)74 (4.4)1.1 (0.76–1.52)
12-Month prevalence of eczema symptoms
Eczema128 (7.3) 123 (6.6) 0.9 (0.69–1.17)114 (6.7) 163 (9.8) 1.5 (1.18–1.97)
Average nights of sleeplessness
 None87 (5.0)90 (4.8)1.0 (0.71–1.33)68 (4.0)114 (6.8) 1.8 (1.29-2.45)
 Any38 (2.2)31 (1.7)0.8 (0.46–1.26)45 (2.6)49 (2.9) 1.1 (0.73–1.73)
Lifetime diagnosis
Eczema ever251 (14.3)253 (13.6)0.9 (0.77–1.13)250 (14.6)282 (16.9)1.2 (0.99–1.44)
Table 3.  Time trends of symptoms, severity, and diagnosis of asthma, allergic rhinitis, and atopic eczema among 13–14 year olds* in Münster
 BoysGirls
1994/1995 survey (N = 1865)1999/2000 survey (N = 1894)POR (95% CI)1994/1995 survey (N = 1892)1999/2000 survey (N = 1922)POR (95% CI)
n (%)n (%)n (%)n (%)
  1. * Self-report. ** P < 0.05 for the difference in odds ratios corresponding to the two levels of severity (none vs any) using the test of homogeneity of the odds ratios.

12-Month prevalence of asthma symptoms
Wheeze241 (12.9)288 (15.2)1.2 (1.0–1.46)289 (15.3)378 (19.7)1.4 (1.15–1.62)
Night cough303 (16.2)332 (17.5)1.1 (0.90–1.28)451 (23.8)549 (28.6)1.3 (1.09–1.47)
Exercise-induced wheeze359 (19.2)429 (22.7)1.2 (1.04–1.44)441 (23.3)558 (29.0)1.3 (1.14–1.54)
Number of wheeze attacks
 None21 (1.1)33 (1.7)1.6 (0.87–2.78)36 (1.9)25 (1.3)0.7 (0.39–1.17)
 Any208 (11.2)253 (13.4)1.2 (1.0–1.49)246 (13.0)345 (18.0)1.5** (1.22–1.76)
Speech limiting wheeze
 None146 (7.8) 170 (9.0) 1.2 (0.92–1.47)173 (9.1) 209 (10.9)1.2 (0.97–1.51)
 Any88 (4.7)111 (5.9) 1.2 (0.93–1.69)110 (5.8) 165 (8.6) 1.5 (1.17–1.97)
Sleep disturbance due to wheeze
 None177 (9.5) 220 (11.6)1.3 (1.01–1.55)189 (10.0)249 (13.0)1.3 (1.09–1.65)
 Any54 (2.9)63 (3.3)1.2 (0.78–1.69)94 (5.0)121 (6.3) 1.3 (0.97–1.71)
Lifetime diagnosis
Asthma ever166 (8.9)166 (8.8) 1.0 (0.78–1.24)95 (5.0)132 (6.9) 1.4 (1.05–1.84)
12-Month prevalence of rhinitis symptoms
Rhinitis508 (27.2)524 (27.7)1.0 (0.88–1.18)582 (30.8)695 (36.2)1.3 (1.11–1.46)
Rhino-conjunctivitis248 (13.3)210 (11.1)0.8 (0.66–0.99)298 (15.8)366 (19.0)1.3 (1.05–1.49)
Interference with daily activities
 None204 (10.9)211 (11.1)1.0 (0.82–1.25)258 (13.6)315 (16.4)1.2 (1.02–1.46)
 Any258 (13.8)282 (14.9)1.1 (0.90–1.30)262 (13.8)347 (18.1)1.4 (1.13–1.61)
Lifetime diagnosis
Hay fever ever424 (22.7)468 (24.7)1.1 (0.93–1.27)360 (19.0)429 (22.3)1.2 (1.04–1.43)
12-Month prevalence of eczema symptoms
Eczema93 (5.0)85 (4.5)0.9 (0.66–1.22)178 (9.4) 214 (11.1)1.2 (0.98–1.50)
Average nights of sleeplessness
 None71 (3.8)49 (2.6)0.7 (0.46–0.99)115 (6.1) 132 (6.7) 1.1 (0.87–1.49)
 Any20 (1.1)32 (1.7)1.6** (0.88–2.89)60 (3.2)81 (4.2)1.3 (0.94–1.91)
Lifetime diagnosis
Eczema ever153 (8.2) 206 (10.9)1.4 (1.09–1.71)233 (12.3)334 (17.4)1.5 (1.22–1.77)
image

Figure 1. Absolute percentage change in 12-month prevalence of symptoms of asthma, allergic rhinitis, and atopic eczema for boys and girls in both age groups.

Download figure to PowerPoint

Table 4.  Time trends of 12-month (current) symptoms of asthma among 13–14 year olds from the video questionnaire
 BoysGirls
1994/1995 survey (N = 1865)1999/2000 survey (N = 1894)POR (95% CI)1994/1995 survey (N = 1892)1999/2000 survey (N = 1922)POR (95% CI)
n (%)n (%)n (%)n (%)
Wheeze while at rest111 (6.0) 122 (6.4) 1.1 (0.83–1.43)105 (5.5) 142 (7.4) 1.4 (1.04–1.78)
Wheeze with exercise238 (12.8)286 (15.1)1.2 (1.0–1.46)380 (20.1)406 (21.1)1.1 (0.91–1.25)
Sleep disturbance due to wheeze72 (3.9)74 (3.9)1.0 (0.72–1.43)69 (3.6)105 (5.5) 1.5 (1.11–2.12)
Sleep disturbance due to cough135 (7.2) 174 (9.2) 1.3 (1.02–1.66)262 (13.8)378 (19.7)1.5 (1.27–1.81)
Severe wheeze84 (4.5)80 (4.2)0.9 (0.68–1.30)72 (3.8)108 (5.6) 1.5 (1.10–2.07)

Discussion

  1. Top of page
  2. Abstract
  3. Methods
  4. Population and data collection
  5. Outcome measures
  6. Data analysis
  7. Results
  8. Discussion
  9. Acknowledgments
  10. References

With the rigorous application of identical study methods, attainment of high and similar response rates in both surveys and for both age groups, and the use of a large sample representative of children within the general population, we believe that we have arrived at credible estimates of time trends of the prevalence of symptoms of asthma, allergic rhinitis, and atopic eczema within the studied population. Our data show that there is a general tendency towards an increase in the symptoms of these disorders among children in Münster, remarkably more so among girls than boys.

The two main concerns about questionnaire-based surveys for the epidemiological study of asthma and allergies are the ability of questionnaires to catch the clinical spectrum of the problem of interest, and the liability of questionnaire-gathered information to the change in awareness or diagnostic labelling (23–25). These concerns are particularly relevant for the study of childhood asthma, where presentation can vary across a considerable range of symptoms and where we have no gold standard against which we can validate our questionnaires (26, 27). Furthermore, increased public attention to asthma in recent years can affect awareness or perception of symptoms, rendering studying time trends troublesome. Indeed, Man Kwong et al. have recently found, using the ISAAC questionnaire, that the increase in 12-month symptoms of asthma among children aged 8–9 years in Sheffield, England, was confined to mild symptoms, arguing for a possible contribution of over-reporting of mild symptoms, as a result of increased awareness, to the increasing trends of asthma in their population (28). Furthermore, improvement in treatment can affect the severity profile of asthma symptoms, leading to an increase in the reporting of less severe symptoms (28, 29). However, we believe that the overall increase in the three conditions we report here reflects for the most part a genuine increase in their morbidity within the community. First, we focused in our assessment of time trends on the change in symptoms of the three disease entities, which should be less susceptible to change in the diagnostic behaviour of health-care providers. In addition, for most of the studied strata the 5-year increase in current symptoms (12 months) surpassed the increase in indices related to the diagnosis of these conditions, which argues against a change in diagnostic behaviour of physicians as an important contributor to the noticed time trends. Second, the fact that in the case of asthma the 5-year increase of symptoms within each stratum was homogenous for all assessed symptoms, and that in all three conditions the noticed increase in prevalence did not generally show a differential severity profile, rules out the possibility of an important contribution of change in severity or awareness of mild symptoms to the noticed time trends. Finally, for the 13–14 year olds, responses to the written and video questionnaires draw an analogous picture of the general trends towards an increase in asthma symptoms and severity, mostly among girls, giving further support to the validity of our observed trends.

Intriguingly, the most pronounced pattern found in this study was gender-related, with girls having more pronounced increase in the prevalence of symptoms of all three conditions compared to boys. For example, current wheeze among girls in the 6–7-year age group witnessed a 70% relative increase within the 5-year study period compared to only 13% increase for boys in the same age group. This is an important finding that can be overlooked by reporting figures of time trends without stratification by gender (28, 30). The same pattern was also seen for allergic rhinitis and atopic eczema although on a smaller scale for eczema. Venn and colleagues looked at time trends (1988–1995) in asthma among schoolchildren aged 4–11 years in Nottingham, England, and found that the increase in asthma symptoms was greater in girls than in boys (31). Similar gender-related trends in the occurrence of asthma and allergies were reported among 7–13-year-old schoolchildren in Norway (32). Generally, the natural history of asthma and allergic rhinitis points towards male predominance in childhood but a female predominance from adolescence onward (25, 33). Considering this natural history, our results show that the noticed gender-related time trend works to mitigate the gender difference in respiratory and nasal symptoms in childhood, while probably augmenting it (towards more female dominance) in adolescent years. Atopic eczema, on the other hand, has a known female predominance and a tendency towards subsiding in adolescence (24). This corresponds with our results, which show that the increase of symptoms of eczema was only noticed among girls in both age groups, but more so in the younger age group. In addition, the described age–gender pattern of atopic eczema explains why among the older age group indices of medical diagnosis, which reflect mostly lifetime morbidity, surpassed those related to current symptoms. It is of note that atopic eczema among boys was the only condition that did not increase within the 5-year interval in both age groups.

Apart from time trends, a comparison of the frequency of asthma symptoms with asthma diagnosis at each point of time (1994/1995 and 1999/2000 surveys) suggests that adolescent girls are less likely to report asthma diagnosis compared to adolescent boys. Similar findings have been reported from 13–14-year-old students in Belgium using the ISAAC questionnaire, where the prevalence of asthma symptoms among girls was higher than among boys while the opposite was true for asthma diagnosis (34). Wieringa et al. suggest that their finding can be due either to under-diagnosis of asthma among girls or under-reporting of symptoms by boys in this age group (34). However, given the homogenous picture arising from comparing all responses between boys and girls, our data suggest that the discrepancy between reporting of symptoms and diagnosis of asthma among adolescent girls is most likely to reflect under-diagnosis of asthma among girls. Evidence from Switzerland and Denmark looking at asthma symptoms and diagnosis among school children suggest that asthma is particularly under-diagnosed among girls (35, 36).

In addition to the concerns mentioned earlier about measuring asthma and allergies in questionnaire-based surveys (9), we ought to remember that although incidence can be inferred from prevalence the cross-sectional design gives no direct information about the incidence of asthma or allergy. Prevalence, in turn, can be influenced by a variety of factors, such as remission, exacerbation, and treatment. However, given the chronic nature of the three studied conditions and the length of the inquiry period (12 months), the calculated estimates reflect to a good extent the morbidity of these conditions within the society at each point in time. In addition, differential recall due to a multitude of disease-related (i.e. severity) or personal (i.e. socio-economic) factors can influence the quality of gathered information, but this would have minimal effect on the current analyses, since it is unlikely that these factors have changed considerably within 5 years. On the other hand, the use of identical methodology and the full compliance with the strict methodological and quality control measures of the ISAAC study in both surveys make us quite positive about the validity of our assessment and conclusions.

Trying to speculate on the reasons behind the observed time trends however, especially the female predominance, is not a simple task. We recently looked at the smoking habits of adolescents in the same surveys and found that the increase in current smoking was more marked among girls compared to boys (37). Smoking, however, is not likely to be of much importance in explaining the observed gender difference in time trends as it cannot explain the steeper increase in symptoms of asthma and eczema, in the younger age group. Recent evidence has shown that although genetic factors influence susceptibility to sensitization and allergic disease, identical twins show discordance in their expression of atopic symptoms (38). Furthermore, atopy (the propensity to mount IgE-mediated responses to common allergens), which is the strongest risk factor for asthma and allergies, seems to play a minor role in some populations, as studies from Africa and China suggest (39, 40). In a broader sense, there is ample evidence showing that children with more dynamic lifestyles (children in rural areas, more physically active, raised on a farm, in some traditional cultures) seem to be relatively protected from asthma and allergy (41–46). Accordingly, it seems that some environmental influences associated with more traditional lifestyles can confer resistance to the development of allergies even in susceptible individuals, and that the expression of asthma and allergies is governed by a dynamic balance between protective/risk factors at each stage of development. It is plausible, therefore, that, due to a mixture of social and biological factors, girls, especially in western/urban settings, can be more vulnerable to lifestyle factors that will interfere with their ability to develop normal resistance to allergy (47). Indeed, evidence from the two largest studies to date, looking at the effect of siblings on the occurrence of allergy, found a stronger protective effect for brothers than for sisters (48, 49), which can reflect the influence of male siblings (especially older ones) in determining the level of physical activity of his brother/sister as well as their ability to spend more time outdoors. Furthermore, Andrew-Aligne and colleagues have been able to show recently that the higher prevalence of asthma among inner city black children is not due to race or low income per se, but more so due to their living in an urban setting (50), highlighting the importance of the social context within which asthma and allergy develop. Thus, although this view does not give specific mechanisms/answers to the noticed gender-related time trends, it can provide a useful framework for future research looking in depth into factors influencing different trends of asthma and allergies within the population.

Back to our main question, is the prevalence of asthma and allergies increasing? Recent evidence from children in Italy and adults in Great Britain suggests that the increase in asthma observed in the 1970s and 1980s may be coming to an end (51, 52). We show in this report, however, that symptoms of asthma and allergies in our population continue to show an increasing trend. This trend is likely to reflect a real change in the morbidity of these conditions within our population as it spans the whole spectrum of symptoms and severity levels.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Methods
  4. Population and data collection
  5. Outcome measures
  6. Data analysis
  7. Results
  8. Discussion
  9. Acknowledgments
  10. References

This study was funded by the Ministry for Women, Youth, Family and Health of the State of North Rhine-Westphalia, Düsseldorf. Dr. Wasim Maziak is supported by a fellowship from the Alexander von Humboldt Foundation, Bonn, Germany.

References

  1. Top of page
  2. Abstract
  3. Methods
  4. Population and data collection
  5. Outcome measures
  6. Data analysis
  7. Results
  8. Discussion
  9. Acknowledgments
  10. References
  • 1
    Kay AB. Allergy and allergic diseases. First of two parts. N Engl J Med 2001;344: 3037.
  • 2
    Strachan DP. Parallels with the epidemiology of other allergic diseases. In: WilliamsHC, editor. The epidemiology of atopic dermatitis. Cambridge: Cambridge University Press, 2000: 221232.
  • 3
    Beasley R, Keil U, von Mutius E, Pearce N. Worldwide variation in prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema: ISAAC. The International Study of Asthma and Allergies in Childhood (ISAAC). Lancet 1998;351: 12251232.
  • 4
    Kuehni CE, Davis A, Brooke AM, Silverman M. Are all wheezing disorders in very young (preschool) children increasing in prevalence? Lancet 2001;357: 18211825.
  • 5
    Sterk PJ, Buist SA, Woolcock AJ, Marks GB, Platts-Mills TA, von Mutius E, Bousquet J, Frew AJ, Pauwels RA, Ait-Khaled N, Hill SL, Partridge MR. The message from the World Asthma Meeting. Eur Respir J 1999;14: 14351453.
  • 6
    von Mutius E, Weiland SK, Fritzsch C, Duhme H, Keil U. Increasing prevalence of hay fever and atopy among children in Leipzig, East Germany. Lancet 1998;351: 862866.
  • 7
    Sears MR. Descriptive epidemiology of asthma. Lancet 1997;350 (Suppl. 2):SII1SII4.
  • 8
    Strachan DP. The epidemiology of childhood asthma. Allergy 1999;54 (Suppl. 49):711.
  • 9
    Magnus P, Jaakkola JJ. Secular trend in the occurrence of asthma among children and young adults: critical appraisal of repeated cross sectional surveys. Br Med J 1997;314: 17951799.
  • 10
    von Mutius E. The rising trends in asthma and allergic disease. Clin Exp Allergy 1998;28 (Suppl. 5):4549.
  • 11
    Sterk PJ, Buist SA, Woolcock AJ, Marks GB, Platts-Mills TA, von Mutius E, Bousquet J, Frew AJ, Pauwels RA, Ait-Khaled N, Hill SL, Partridge MR. The message from the World Asthma Meeting.The Working Groups of the World Asthma Meeting, held in Barcelona, Spain, December 9–13, 1998. Eur Respir J 1999;14: 14351453.
  • 12
    Asher MI, Weiland SK. The International Study of Asthma and Allergies in Childhood (ISAAC). ISAAC Steering Committee. Clin Exp Allergy 1998;28 (Suppl. 5):5266.
  • 13
    Lewis S. ISAAC  – a hypothesis generator for asthma? International Study of Asthma and Allergies in Childhood. Lancet 1998;351: 12201221.
  • 14
    Asher MI, Keil U, Anderson HR, Beasley R, Crane J, Martinez F, Mitchell EA, Pearce N, Sibbald B, Stewart AW, Strachan D, Weiland SK, Williams HC. International Study of Asthma and Allergies in Childhood (ISAAC): rationale and methods. Eur Respir J 1995;8: 483491.
  • 15
    Duhme H, Weiland SK, Rudolph P, Wienke A, Kramer A, Keil U. Asthma and allergies among children in West and East Germany: a comparison between Münster and Greifswald using the ISAAC phase I protocol. Eur Respir J 1998;11: 840847.
  • 16
    Pearce N, Weiland S, Keil U, Langridge P, Anderson HR, Strachan D, Bauman A, Young L, Gluyas P, Ruffin D, Crane J, Beasley R. Self-reported prevalence of asthma symptoms in children in Australia, England, Germany and New Zealand: an international comparison using the ISAAC protocol. Eur Respir J 1993;6: 14551461.
  • 17
    ISAAC Phase One Manual, 2nd edn, Auckland, New Zealand/Münster, Germany, 1993.
  • 18
    ISAAC Phase Three Manual. Auckland, New Zealand, 2000.
  • 19
    The International Study of Asthma and Allergies in Childhood (ISAAC) Steering Committee. Worldwide variations in the prevalence of asthma symptoms: the International Study of Asthma and Allergies in Childhood (ISAAC). Eur Respir J. 1998;12: 315335.
  • 20
    Strachan D, Sibbald B, Weiland S, Ait-Khaled N, Anabwani G, Anderson HR, Asher MI, Beasley R, Björksten B, Burr M, Clayton T, Crane J, Ellwood P, Keil U, Lai C, Mallol J, Martinez F, Mitchell E, Montefort S, Pearce N, Robertson C, Shah J, Stewart A, von Mutius E, Williams H. Worldwide variations in prevalence of symptoms of allergic rhinoconjunctivitis in children: the International Study of Asthma and Allergies in Childhood (ISAAC). Pediatr Allergy Immunol 1997;8: 161176.
  • 21
    Williams H, Robertson C, Stewart A, Ait-Khaled N, Anabwani G, Anderson R, Asher I, Beasley R, Björksten B, Burr M, Clayton T, Crane J, Ellwood P, Keil U, Lai C, Mallol J, Martinez F, Mitchell E, Montefort S, Pearce N, Shah J, Sibbald B, Strachan D, von Mutius E, Weiland SK. Worldwide variations in the prevalence of symptoms of atopic eczema in the International Study of Asthma and Allergies in Childhood. J Allergy Clin Immunol 1999;103 (1 Pt 1):125138.
  • 22
    Kaur B, Anderson HR, Austin J, Burr M, Harkins LS, Strachan DP, Warner JO. Prevalence of asthma symptoms, diagnosis, and treatment in 12–14 year old children across Great Britain (international study of asthma and allergies in childhood, ISAAC UK). Br Med J 1998;316: 118124.
  • 23
    Jarvis D, Burney PGJ. Epidemiology of asthma. In: BusseWW, HolgateST, eds. Asthma and rhinitis, 2nd edn. Oxford: Blackwell Scientific Publications, 2000: 1732.
  • 24
    Williams HC. Inflammatory skin diseases I: atopic dermatitis. In: WilliamsHC, StrachanDP, eds. The challenge of dermato-epidemiology. Boca Raton, NY: CRC Press, 1997: 125144.
  • 25
    Strachan DP. Epidemiology of rhinitis. In: BusseWW, HolgateST, eds. Asthma and rhinitis, 2nd edn. Oxford: Blackwell Scientific Publications, 2000: 3342.
  • 26
    Peat JK, Toelle BG, Marks GB, Mellis CM. Continuing the debate about measuring asthma in population studies. Thorax 2001;56: 406411.
  • 27
    Pekkanen J, Pearce N. Defining asthma in epidemiological studies. Eur Respir J 1999;14: 951957.
  • 28
    Ng Man Kwong G, Proctor A, Billings C, Duggan R, Das C, Whyte MK, Powell CV, Primhak R. Increasing prevalence of asthma diagnosis and symptoms in children is confined to mild symptoms. Thorax 2001;56: 312314.
  • 29
    Anderson HR, Butland BK, Strachan DP. Trends in prevalence and severity of childhood asthma. Br Med J 1994;308: 16001604.
  • 30
    Kalyoncu AF, Selcuk ZT, Enunlu T, Demir AU, Coplu L, Sahin AA, Artvinli M. Prevalence of asthma and allergic diseases in primary school children in Ankara, Turkey: two cross-sectional studies, five years apart. Pediatr Allergy Immunol 1999;10: 261265.
  • 31
    Venn A, Lewis S, Cooper M, Hill J, Britton J. Increasing prevalence of wheeze and asthma in Nottingham primary schoolchildren 1988–1995. Eur Respir J 1998;11: 13241328.
  • 32
    Selnes A, Bolle R, Holt J, Lund E. Cumulative incidence of asthma and allergy in north-Norwegian schoolchildren in 1985 and 1995. Pediatr Allergy Immunol 2002;13: 5863.
  • 33
    Stender M, Weiland SK, Duhme H, Keil U. Epidemiology of asthma and allergic disease. In: Environmental Health Criteria 212, Principles and Methods for Assessing Allergic Hypersensitization Associated with Exposure to Chemicals. Geneva: World Health Organization, 1999: 224271.
  • 34
    Wieringa MH, Weyler JJ, Van Bever HP, Nelen VJ, Vermeire PA. Gender differences in respiratory, nasal and skin symptoms: 6–7 versus 13–14-year-old children. Acta Paediatr 1999;88: 147149.
  • 35
    Sennhauser FH, Kuhni CE. Prevalence of respiratory symptoms in Swiss children: is bronchial asthma really more prevalent in boys? Pediatr Pulmonol 1995;19: 161166.
  • 36
    Siersted HC, Boldsen J, Hansen HS, Mostgaard G, Hyldebrandt N. Population based study of risk factors for underdiagnosis of asthma in adolescence: Odense schoolchild study. Br Med J 1998;316: 651655.
  • 37
    Maziak W, Rzehak P, Keil U, Weiland SK. Smoking among adolescents in Münster, Germany (1995–2000): increase in prevalence and relation to tobacco advertising. Prev Med 2003;36: 172176.
  • 38
    Strachan DP, Wong HJ, Spector TD. Concordance and interrelationship of atopic diseases and markers of allergic sensitization among adult female twins. J Allergy Clin Immunol 2001;108: 901907.
  • 39
    Leung R, Ho P. Asthma, allergy, and atopy in three south-east Asian populations. Thorax 1994;49: 12051210.
  • 40
    Weinberg EG. Urbanization and childhood asthma: an African perspective. J Allergy Clin Immunol 2000;105 (2 Pt 1):224231.
  • 41
    Hijazi N, Abalkhail B, Seaton A. Asthma and respiratory symptoms in urban and rural Saudi Arabia. Eur Respir J 1998;12: 4144.
  • 42
    Huovinen E, Kaprio J, Laitinen LA, Koskenvuo M. Social predictors of adult asthma: a co-twin case–control study. Thorax 2001;56: 234236.
  • 43
    Maziak W. Asthma and farming. Lancet 2002;359: 623624.
  • 44
    Kearney PM, Kearney PJ. The prevalence of asthma in schoolboys of travellers’ families. Ir Med J 1998;91: 203206.
  • 45
    Alm J, Swartz J, Lilja G, Scheynius A, Pershagen G. Atopy in children of families with an anthroposophic lifestyle. Lancet 1999;353: 14851488.
  • 46
    Isolauri E, Rautava S, Kalliomaki M, Kirjavainen P, Salminen S. Role of probiotics in food hypersensitivity. Curr Opin Allergy Clin Immunol 2002;2: 263271.
  • 47
    Maziak W. Asthma and the exposure-disease tenet. J Clin Epidemiol 2002;55: 737740.
  • 48
    Svanes C, Jarvis D, Chinn S, Burney P. Childhood environment and adult atopy: results from the European Community Respiratory Health Survey. Allergy Clin Immunol 1999;103: 415420.
  • 49
    Strachan DP, Harkins LS, Golding J. Sibship size and self-reported inhalant allergy among adult women. Clin Exp Allergy 1997;27: 151155.
  • 50
    Andrew Aligne C, Auinger P, Byrd RS, Weitzman M. Risk factors for pediatric asthma. Contributions of poverty, race, and urban residence. Am J Respir Crit Care Med 2000;162 (3 Pt1):873877.
  • 51
    Fleming DM, Sunderland R, Cross KW, Ross AM. Declining incidence of episodes of asthma: a study of trends in new episodes presenting to general practitioners in the period 1989–98. Thorax 2000;55: 657661.
  • 52
    Ronchetti R, Villa MP, Barreto M, Rota R, Pagani J, Martella S, Falasca C, Paggi B, Guglielmi F, Ciofetta G. Is the increase in childhood asthma coming to an end? Findings from three surveys of schoolchildren in Rome, Italy. Eur Respir J 2001;17: 881886.