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Asthma in school age: prevalence, incidence and remission in relation to environmental determinants. The Obstructive Lung Disease in Northern Sweden (OLIN) Studies, Thesis XI
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine. (OLIN-studierna)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background In the past half-century, the prevalence of asthma among children and adolescents has risen and asthma has become an important public health challenge in Sweden as well as in many other countries, necessitating further studies on this complex disease and its risk factor pattern. The studies included in this thesis aimed to investigate the clinical expression of childhood asthma over time, to describe the determinants of new-onset and remission of asthma, and to evaluate possible environmental risk factors in northern Sweden.

Methods As the result of a repeated questionnaire survey among primary school children aged 7-8 years in three municipalities in the north of Sweden, two pediatric cohorts were formed, one in 1996 (n=3430) and one in 2006 (n=2585). The cohort created in 1996 was followed annually until the age of 19 years. Skin prick testing was performed on children in both cohorts. Lung function and bronchial hyperreactivity testing were carried out in children with asthma in the first cohort. The study participation and retention rates were very high in both cohorts. Among children in the second cohort living in Luleå, the home addresses were assigned to coordinates in a geographical information system (GIS) to evaluate the impact on respiratory health of living near roads with much traffic, which was measured as the number of vehicles daily. We used a validated reported diagnosis of asthma and International Study of Asthma and Allergies in Childhood (ISAAC) questions were incorporated into the questionnaire. A cross-sectional study of children of the same age ten years apart, longitudinal studies on asthma incidence and remission as well as a cross-sectional study on vehicle traffic were performed.

Results While children aged 7-8 years in 2006 more often had a physician-diagnosed asthma compared to children of the same age in 1996 (7.4% vs 5.7%, p<0.001), they had less asthma symptoms, especially severe symptoms. In parallel, a more beneficial environment and a more intense treatment with inhaled corticosteroids (ICS) were observed. The explanation for this change in clinical expression probably includes also an increased awareness and diagnosing of asthma. From age 12 years to age 19 years, the cumulative incidence of physician-diagnosed asthma was 7.2% and of current wheeze 22.0%. The risk of new-onset asthma in adolescence was increased among girls, sensitized and those with heredity for asthma. Smoking and home dampness increased the risk for incident wheeze. The risk for both incident asthma and wheeze was inversely related to number of siblings. Among children with current asthma at age 7-8 years, 21% were in remission, 38% had periodic asthma and 41% had persistent asthma at a follow-up at age 19 years. Subjects in remission and with periodic asthma had significantly less airway obstruction and showed less bronchial hyperreactivity compared to subjects with persistent asthma. The probability of asthma remission from childhood to early adulthood was significantly increased by absence of allergic sensitization, male gender and a low asthma severity scoring at age 7-8 years. Sensitization to furred animals was more important as a determinant of both incidence and remission than sensitization to pollen. Living close to roads with high traffic flows, especially with heavy vehicles, was associated with an increased risk for current wheeze. Stratified analyses showed that the effect of traffic on asthma and wheeze was restricted to non-sensitized subjects.

Conclusion Asthma onset in adolescence was more common among girls and remission was more common among boys. Children sensitized to furred animals and children with a more severe asthma were risk groups for persistence of asthma. Environmental factors such as smoking and dampness were associated to onset of asthma symptoms during adolescence, and vehicle traffic was associated with asthma symptoms among children also in a small city with relatively low traffic flows. Preventive measures like smoking reduction programs, improvement of damp housing conditions and separation of areas where many children live from heavily trafficked roads could prove to be beneficial.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet , 2013. , 66 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1565
Keyword [en]
asthma, wheeze, environment, prevalence, incidence, remission, vehicle traffic, sensitization
National Category
Other Clinical Medicine
Research subject
Occupational and Environmental Medicine
Identifiers
URN: urn:nbn:se:umu:diva-69623ISBN: 978-91-7459-595-6 (print)OAI: oai:DiVA.org:umu-69623DiVA: diva2:619448
Public defence
2013-05-29, Sal 135, by 9A, Norrlands Universitetssjukhus, Umeå, 13:00 (Swedish)
Opponent
Supervisors
Projects
OLIN-studierna
Available from: 2013-05-07 Created: 2013-05-03 Last updated: 2013-05-07Bibliographically approved
List of papers
1. The clinical expression of asthma in schoolchildren has changed between 1996 and 2006
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2010 (English)In: Pediatric Allergy and Immunology, ISSN 0905-6157, E-ISSN 1399-3038, Vol. 21, no 5, 859-866 p.Article in journal (Refereed) Published
Abstract [en]

Several studies have reported diverging trends in the prevalence of asthma and wheeze. The aim of this study was to investigate the clinical expression of childhood asthma in 1996 and 2006 by studying asthma morbidity, treatment, and environmental exposures in school children with physician-diagnosed asthma and wheeze, respectively. All children enrolled in first or second grade (7-8 yr-old) in three municipalities in northern Sweden were invited to a questionnaire study in 1996 and 2006, respectively. In 1996, 3430 (97%) participated; and in 2006, 2585 (96%) participated. The same parental completed questionnaire, including the ISAAC questions, was used in both surveys. Physician-diagnosed asthma was reported at 5.7% in 1996 and 7.4% in 2006. A significantly greater proportion of children with asthma were using inhaled corticosteroids (ICS) in 2006, 67% vs. 55% in 1996. This increase was parallel to a major decrease in severe asthma symptoms such as disturbed sleep because of wheeze (49% vs. 38%) and troublesome asthma (21% vs. 11%). The prevalence of current wheeze among the asthmatics decreased significantly; however, this was seen only among children not using ICS. Parental smoking decreased significantly as did the proportion living in damp buildings. In conclusion, although asthma remains a major public health issue in school age children, children with asthma had less respiratory symptoms and a better asthma control in 2006 compared to 1996. This parallels with an increase in treatment with ICS, more beneficial environmental conditions, and an increased diagnostic intensity resulting in a larger proportion of children with mild symptoms being diagnosed as having asthma.

Keyword
asthma;children;epidemiology;medication;environment
National Category
Respiratory Medicine and Allergy Immunology in the medical area Pediatrics
Identifiers
urn:nbn:se:umu:diva-34782 (URN)10.1111/j.1399-3038.2010.01055.x (DOI)000280200000009 ()20408972 (PubMedID)
Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2017-12-12Bibliographically approved
2. Heavy vehicle traffic is related to wheeze among schoolchildren: a population-based study in an area with low traffic flows
Open this publication in new window or tab >>Heavy vehicle traffic is related to wheeze among schoolchildren: a population-based study in an area with low traffic flows
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2011 (English)In: Environmental health, ISSN 1476-069X, E-ISSN 1476-069X, Vol. 10, no 91Article in journal (Refereed) Published
Abstract [en]

Background: An association between traffic air pollution and respiratory symptoms among children has been reported. However, the effects of traffic air pollution on asthma and wheeze have been very sparsely studied in areas with low traffic intensity in cold climate with poor dispersion. We evaluated the impact of vehicle traffic on childhood asthma and wheeze by objective exposure assessment.

Methods: As a part of the Obstructive Lung Disease in Northern Sweden (OLIN) studies, a questionnaire was sent to the families of all children attending first or second grade in Luleå (72,000 inhabitants) in Northern Sweden in 2006. The age of the children was 7-8 years and the participation rate was 98% (n = 1357). Skin prick tests were performed in 1224 (89%) children. The home addresses were given geographical coordinates and traffic counts were obtained from the local traffic authorities. A proximity model of average daily traffic and average daily heavy vehicle traffic within 200 meters from each participant's home address was used. The associations between traffic exposure and asthma and wheeze, respectively, were analysed in an adjusted multiple logistic regression model.

Results: Exposure to high traffic flows was uncommon in the study area; only 15% of the children lived within 200 meters from a road with a traffic flow of ≥8000 vehicles per day. Living closer than 200 meters from a road with ≥500 heavy vehicles daily was associated with current wheeze, odds ratio 1.7 (confidence interval 1.0-2.7). A dose-response relation was indicated. An increased risk of asthma was also seen, however not significant, odds ratio 1.5 (confidence interval 0.8-2.9). Stratified analyses revealed that the effect of traffic exposure was restricted to the non-sensitized phenotype of asthma and wheeze. The agreement between self-reported traffic exposure and objective measurements of exposure was moderate.

Conclusions: This study showed that already at low levels of exposure, vehicle traffic is related to an increased risk of wheeze among children. Thus, the global burden of traffic air pollution may be underestimated.

Place, publisher, year, edition, pages
London: BioMed Central, 2011
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-49214 (URN)10.1186/1476-069X-10-91 (DOI)21995638 (PubMedID)
Available from: 2011-11-04 Created: 2011-11-04 Last updated: 2017-12-08Bibliographically approved
3. Persistence and remission of asthma followed from 7 to 19 years of age
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(English)Manuscript (preprint) (Other academic)
National Category
Respiratory Medicine and Allergy
Identifiers
urn:nbn:se:umu:diva-70206 (URN)
Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2013-05-07Bibliographically approved
4. Incidence of wheeze and asthma in adolescence in relation to environmental factors
Open this publication in new window or tab >>Incidence of wheeze and asthma in adolescence in relation to environmental factors
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(English)Manuscript (preprint) (Other academic)
National Category
Respiratory Medicine and Allergy
Identifiers
urn:nbn:se:umu:diva-70208 (URN)
Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2013-05-07Bibliographically approved

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