Leticia Grize Institute of Social and Preventive Medicine University of Basel Steinengraben 49 CH-4051 Basel Switzerland
Background: Changing occurrence rates of asthma, allergic rhinitis and atopic dermatitis are of public health concern and require surveillance. Changes in prevalence rates of these atopic diseases were monitored during 10 years and their trend with time was determined taking into account the influence of personal and environmental risk factors.
Methods: Four cross-sectional surveys in 5–7-year old children were performed in seven different communities in Switzerland between 1992 and 2001. Prevalence of respiratory and allergic symptoms and of affecting risk factors including parental environmental concern were assessed using a standardized parental questionnaire.
Results: A total of 988 (74.1%), 1778 (79.0%), 1406 (82.6%) and 1274 (78.9%) children participated, respectively, in the 1992, 1995, 1998 and 2001 surveys. Prevalence rates of asthma and hay fever symptoms remained quite stable over time (wheeze/past year: 8.8%, 7.8%, 6.4% and 7.4%, sneezing attack during pollen season: 5.0%, 5.6%, 5.4% and 4.6%). Rates of reported atopic dermatitis symptoms (specific skin rash/past year: 4.6%, 6.5%,7.4% and 7.6%) showed an increase over time, but those of diagnosis of eczema did not show a clear pattern (18.4%, 15.7%, 14.0% and 15.2%). Stratified analysis by parental environmental concern and by parental atopy showed similar trends. Rates of atopic dermatitis symptoms showed significant increase in girls but stayed stable in boys.
Conclusion: Results of these four consecutive surveys suggest that the increase in prevalence of asthma and hay fever in 5–7-year old children living in Switzerland may have ceased. However, symptoms of atopic dermatitis may still be on the rise, especially among girls.
Atopic diseases such as asthma, allergic rhinitis and atopic dermatitis are common disorders in childhood and rank high on the public health agenda highlighting the need for continuous monitoring. Time trends in asthma and atopy have shown a substantial increase since the early 1960s and there is evidence of consistent associations of these disorders with Western lifestyle (1). More recently an increasing number of studies reported reversing trends of childhood asthma and atopy since the late 1990s (2). Likewise, the prevalence rates of asthma, allergic rhinitis and atopic sensitization among Swiss adolescents have stabilized since the early 1990s after a clear upward trend during the 1980s (3). However, there are still a number of studies showing a continuous increase in prevalence rates of childhood asthma or allergic rhinitis (4–7) and several studies reported diverging trends according to age group (8, 9), gender (9, 10) or atopic phenotype (7, 11).
Studies on time trends of childhood asthma and atopy usually rely on parental responses to repeated questionnaires and thus might be influenced by changes in public and professional awareness and diagnostic labelling. A recent report from Sheffield, UK (12) found that the increase in the last 12-months prevalence of symptoms of asthma among 8–9 year olds was confined to mild symptoms arguing for a possible contribution of over-reporting of mild symptoms as a result of increased public awareness.
Many environmental factors have been hypothesized to contribute to the increasing asthma and atopy rates including both indoor (13) and ambient air pollution (14), reduced exposure to microbial stimulation (15) and changes in diet (16). However, the observed increase has not convincingly been explained by any of these factors and there is limited evidence of changes in exposure to these risk factors over time.
The present study, Swiss Surveillance Programme on Childhood Allergy and Respiratory symptoms with respect to Air Pollution and Climate (SCARPOL) (17), was set up in 1992 to monitor the development of asthma and allergy rates over time in children attending school in Switzerland by investigating the same age group of children with the same methodology every 3 years.
We report here the outcome of four consecutive surveys conducted among 5–7-year old children using the questionnaire of the International Study of Asthma and Allergies in Childhood (ISAAC) and assessing a range of environmental exposures over time. We specifically examined whether changes in the amount of parental environmental concern with respect to their children's health influences time trend of reported symptoms and whether the time trend was similar in boys and girls and for the different atopic phenotypes.
The Swiss Surveillance Programme of Childhood Allergy and Respiratory Symptoms with respect to Air Pollution and Climate (SCARPOL) is a multi-centre study designed to monitor the prevalence rates of respiratory and allergic symptoms and of relevant environmental factors over time. The study consists of repeated cross-sectional surveys organized within the frame of the School Health Services, which includes routine visits during kindergarten or first, fourth and eighth school grades. The present analyses focus on the youngest age group (5–7 year olds). The SCARPOL surveillance study was carried out in three urban centres (Bern, Lugano and Zurich) and four suburban or rural communities (Grabs, Langnau, Montana and Payerne).
A representative sample of schools was invited to participate in the urban centres, while all children of the respective age group were invited in the rural areas. Parents filled in a detailed questionnaire on health outcomes and risk factors based on the core questions on asthma and allergy of the ISAAC study (18). The study protocol was approved by the ethics committees of the Universities of Geneva and Bern.
Responses relating to asthma, hay fever, eczema and their corresponding symptoms obtained from the parental questionnaire were examined as health outcomes. With respect to asthma, answers to questions on wheeze and asthma ever, wheeze during the past year, wheeze during exercise and speech impairment by wheeze were considered. Regarding hay fever, responses to sneezing attack without a cold accompanied by itchy and watery eyes during the past year, to sneezing attack only during pollen season and to the diagnosis of hay fever were analysed. And for eczema, questions asked for an itchy rash which was coming and going for at least 6 months ever or during the past 12 months, and whether this itchy rash had affected any of the following places: the fold of the elbows, behind the knees, in front of the ankles, under the buttocks, around the neck or around the ears or eyes. In addition, parents were asked whether the child ever suffered from eczema. Information on personal risk factors, as well as family characteristics and exposure to potential sources of indoor air pollution were obtained via parental questionnaire. Low parental education was defined as such if none of the parents attended technical school, college or university. Parents were also asked whether they perceived ambient air pollution as a threat to their child's health.
Prevalence of risk factors and potential confounders were determined for each of the four surveys and the time trend was assessed with the Chochran–Armitage test for trend. Raw and adjusted prevalence for all symptoms were calculated. A Generalized Estimating Equations model (19) was used to adjust symptom prevalence for known risk factors and potential confounders and to calculate the time trend. The final models contained all covariates which were either associated with health outcome or had changed significantly over time.
As sensitivity analysis, several stratified multivariate regression models were performed: first, by parental perception of the effect of outdoor air pollution on their children's health, second by the sex of the child, and third by the presence of a family history of asthma and hay fever. All analyses were conducted with SAS Version 8 (20).
In total, parents of 74.1% (988/1333) of the invited children filled in the questionnaires during the 1992 survey, 79.0% (1778/2251) in 1995, 82.6% (1406/1702) in 1998 and 78.9% (1274/1615) in 2001. The characteristics of the study population and the prevalence of the risk factors for the four surveys are shown in Table 1. The mean age of the children decreased from 6.5 to 5.9 (P = <0.0001) due to the shift over time of the visit to the school doctor from first grade to kindergarten in some schools. There was no change on the proportion of participating boys and girls through the years. A statistically significant increase with time was observed for a paternal history of hay fever, the proportion of breastfed children and the number of families who got rid of carpets due to an allergy in the child. The proportion of parents with low education, of homes with water spots or mildew, of carpeted bedrooms, of homes with pets, of children exposed to environmental tobacco smoke through the mother and of parental perception of air pollution as having an influence on children's health showed a significant decrease with time.
Table 1. Characteristics of study population and prevalence of risk factors in four consecutive surveys
1992, n (%)
1995, n (%)
1998, n (%)
2001, n (%)
P-value for trend
Age: mean (SD)
Low parental education
Mother's history of asthma
Father's history of asthma
Mother's history of hay fever
Father's history of hay fever
Environmental tobacco smoke (ETS) exposure by mother
Single oven heating
Water spots or mildew
Carpet in child's bedroom
Pets in child's bedroom
Got rid of carpets due to allergy
Got rid of pets due to allergy
Mother filled in questionnaire
Parents perceive air pollution as a risk factor for respiratory disease in child
Prevalence rates of asthma and hay fever symptoms remained quite stable over the years (Table 2). Yet, the prevalence of symptoms characteristic of atopic eczema/dermatitis syndrome (AEDS) such as skin rash ever and a skin rash during the past year occurring at specific locations showed an increase over time whereas a reported diagnosis of eczema showed no clear pattern. Unadjusted and adjusted time trends showed similar patterns.
Table 2. Raw and adjusted* prevalence rates of asthma, rhinitis and dermatitis symptoms in four consecutive surveys according to parental reports (5–7 years old)
1992 (n = 988)
1995 (n = 1778)
1998 (n = 1406)
2001 (n = 1274)
P-value for trend†
Adjusted, % (95% CI)
Adjusted, % (95% CI)
Adjusted, % (95% CI)
Adjusted, % (95% CI)
*Symptom rates were adjusted for study year, sex, parental education, study area, maternal and paternal asthma and hay fever, breastfeeding, number of siblings, heating system, carpets in child's bedroom, pet ownership, getting rid of carpets because of the child's allergy, exposure to mother's smoking, mother filling in the questionnaire and parental perception of air pollution as a risk factor for their child's respiratory health.
†P-value for trend of adjusted prevalence.
Wheeze past year
Wheeze after exercise
Speech limiting wheeze
Sneezing attack without cold and itchy watery eyes past year
Sneezing attack, only pollen season
Skin rash ever
Specific skin rash past year
Figure 1 shows the adjusted prevalence rates for current symptoms over the four consecutive surveys, stratified by parental perception of air pollution as a risk factor influencing their children's health. Rates of current wheeze and rhinitis symptoms had a tendency to decrease with time in children whose parents were concerned with the influence of the environment. If parents did not have this concern, the rates remained stable and were several times lower. Current dermatitis symptoms increased with time as a tendency in children with parental concern, and significantly in children with parents without environmental concern.
Subgroup analysis by family history of asthma or hay fever showed similar time trends in both strata (results not shown). When stratifying by child's sex, occurrence of all symptoms was slightly higher in boys than in girls (specific rates not shown). Wheeze in the past year decreased from 10.7% to 7.7% (P = 0.048) and speech limiting wheeze from 1.6% to 0.6% (P = 0.026) in boys, and remained unchanged through time in girls. Reported prevalence rates of rhinitis symptoms remained relatively stable in both sexes. As shown in Table 3, reported eczema rates decreased, but AEDS associated symptom rates increased over time, significantly in girls and less obviously in boys. For both sexes the prevalence rates of reported eczema without a typical skin rash decreased significantly over time (in boys from 8.6% in 1992 to 5.6% in 2001, in girls from 9.2% in 1992 to 4.1% in 2001).
Table 3. Adjusted* prevalence of dermatitis symptoms (parental reports) in four consecutive surveys, stratified by children's sex as a risk factor for their child's respiratory health
Study sample/health outcome
1992 % (95% CI)
1995 % (95% CI)
1998 % (95% CI)
2001 % (95% CI)
P-value for trend
*Symptom rates were adjusted for study year, sex, parental education, study area, maternal and paternal asthma and hay fever, breastfeeding, number of siblings, heating system, carpets in child's bedroom, pet ownership, getting rid of carpets because of the child's allergy, exposure to mother's smoking, and mother filling in the questionnaire.
n = 516
n = 872
n = 722
n = 646
Skin rash ever
Specific skin rash past year
n = 472
n = 894
n = 676
n = 620
Skin rash ever
Specific skin rash past year
Among children aged 5–7 years examined in four consecutive surveys between 1992 and 2001 the prevalence rates of asthma and hay fever and associated symptoms remained stable whereas prevalence rates of symptoms characteristic of atopic eczema/dermatitis syndrome significantly increased over these 10 years of observation. This increase was only seen among girls and more pronounced among children whose parents did not express increased awareness of environmental problems and was in contrast to stable rates of reported eczema. Although time trends of a series of known and suspected risk factors for allergic disorders were recorded, the inclusion of these factors into the multivariate analyses did not change the observed time trends. Parental perception of air pollution having a deteriorating effect on their children's health, used as an indicator of increased parental awareness of environmental problems, decreased in prevalence over time but did not affect reported symptom rates differentially. In Switzerland, the increase in the occurrence of asthma and hay fever seems to have plateaued in both adolescents (3) and school-beginners, thus giving no indication of diverging prevalence trends for these phenotypes according to age.
Time trend analyses in other countries performed as part of the ISAAC phase III protocol using the same questions and examining the same age groups of children as the SCARPOL surveillance programme gave inconsistent results. In Spain, responses to the ISAAC questions in 1994 and in 2002 indicated a stabilization of asthma prevalence among adolescents but an increase among the younger age group (8). The ISAAC studies in Hong Kong showed decreasing asthma rates among adolescents (21) and a stabilization of asthma among 6–7 year olds but increasing rates of allergic rhinitis and eczema in this age group (7). In Germany, a significant increase in current symptoms of asthma, rhino-conjunctivitis and eczema among adolescents was observed whereas among the 6–7 year olds the significant increase of reported symptoms was restricted to girls (9). In contrast, a recent study in Southern Germany reported no further increase in the prevalence of asthma and atopy in 10 year olds over a period of 9 years (22). A recent analysis of young adults in Italy indicated stabilization of asthma like symptoms among 32–45 years old but an increase in 20–26 years old (23).
Compared with the observed stabilization of childhood asthma and hay fever prevalence rates in Switzerland, symptoms characteristic of atopic eczema/dermatitis syndrome significantly increased in time, whereas the proportion of children reported to suffer from eczema remained stable. These somewhat inconsistent findings have to be interpreted with caution because the assessment of eczema in epidemiological surveys by means of questionnaires is a particular challenge. The ISAAC questions for ADES symptoms used in the present study have been validated in different parts of the world. They best predicted atopic eczema diagnosed by a dermatologist in the UK (24) performed less well in Germany (25) and showed lowest validity in Ethiopia (26), but the questions have not been validated in Switzerland. Asking parents about a medical diagnosis such as eczema may furthermore yield unreliable results because among lay persons ‘eczema’ is a rather unspecific label for different skin disorders for example contact dermatitis. In addition, the use of medical terms by lay people may change over time, e.g. ‘neurodermitis’ has become an increasingly popular term to describe atopic dermatitis, but our questionnaires did not ask for this label. The decrease over time in reported eczema in children not suffering from a typical rash may, therefore, either be interpreted as indicating a change over time in the use of this diagnostic label by parents or as a decrease in unspecific skin disorders. The observed rise in AEDS associated symptom rates which was predominantly noticed among girls may reflect a real increase in AEDS symptoms. The fact that this increase was mainly observed among children whose parents did not express increased awareness of environmental problems argues against reporting bias due to environmental worry. Yet, as an alternative interpretation, differential parental reporting of skin symptoms for boys and girls cannot be excluded. The interpretation of the present results is obviously limited by the lack of an objective assessment of atopic dermatitis.
It has been suggested that time trends of asthma and allergic diseases may diverge between boys and girls necessitating separate analyses (9, 27). According to a recent study in Norway the prevalence of asthma among 9–11-year old girls reached a plateau and even decreased between 1995 and 2000, whereas asthma prevalence in boys tended to increase over the same time period (10). Conversely, the German ISAAC phase III study found a stronger increase in symptom rates of asthma, rhinitis, and eczema among girls than among boys (9). The present study did not find gender-related differences in the time trend of asthma and allergic rhinitis which is in line with the Spanish ISAAC phase III study (8). However, we observed divergent gender-related trends for AEDS related symptoms.
The present analyses specifically focussed on the role of parental environmental health worry in influencing symptom reporting and thus the assessment of prevalence rates over time. Health effects due to ambient air pollution made the headlines during the 1990s and most parents of children participating in the SCARPOL surveys were concerned about health effects due to environmental pollution in general. However, only about 20% were persuaded that increased levels of air pollution was deleterious to their own child's health. Symptom prevalence rates were several times higher in children with environmentally worried parents, possibly reflecting the fact that parents of susceptible children may see the effect of air pollution as an explanation for their children suffering symptoms. Since the early 1990s both ambient air pollution levels in Switzerland (28) and the proportion of parents who perceive air pollution as a threat to their child's health have declined along with a general decrease of environmental concerns in the Swiss population. A decrease in public awareness of environmentally related health problems may introduce bias in the assessment of time trends of asthma and allergic diseases. However, the results of the present study give no evidence of such bias as the development of prevalence rates over time did not differ between parents with or without environmental concerns.
The underlying reason for the reversing trend in prevalence of asthma and atopy observed in many countries remains still to be elucidated. Factors such as increased professional awareness of asthma, earlier detection and improved treatment have been suggested to be possible causes of changed trends in asthma prevalence (2). In addition, we have previously hypothesized that environmental influences summarized as ‘Western lifestyle’ have been fairly constant during the past decade and may have reached a maximum in inducing atopic disease in susceptible individuals (3).
In conclusion, the results of these four consecutive surveys in 5–7-year old children living in Switzerland suggest that the increase in prevalence of asthma and hay fever may have come to a plateau. However, symptoms of atopic dermatitis may still be on the rise, especially among girls. Environmental concern of the parents did not influence the time trend. Continuing monitoring of these common childhood diseases within the framework of an environmental health surveillance programme is of public health relevance and essential to assess time trends.
The authors are grateful to their many colleagues in the School Health Services who organized the survey. We should also like to thank the children, parents and teachers for their enthusiastic co-operation, which made this investigation possible. The study was supported by a grant of the Swiss National Science Foundation (grant 4026-033109) the Swiss Federal Office of Public Health, the Swiss Federal Office of the Environment, the Lung Association of Zurich and of St Gallen, and the cantonal health services of Zurich, St Gallen, Valais, Vaud, Geneva and Bern.
Conflict of interest statement
None of the authors had any financial or personal relationships with other people or organizations that could inappropriately influence the work associated with the present manuscript.
The SCARPOL team
C. Bezençon, C. Braun-Fahrländer, B. Bringolf, M. I. Carvajal, P. A. Eigenmann, M. Gassner, L. Grize, U. Heininger, U. Neu, P. Schmid-Grendelmeier, F. H. Sennhauser, D. Stamm, P. Straehl, T. Stricker, K. Takken-Sahli, B. Wüthrich.