Biomedical subjects

B Brunekreef

Publications and source records attributed to B Brunekreef.

At least 19 recordsLinked to original sources

PubMed2006

Comparison of parental reports of smoking and residential air nicotine concentrations in children.

BACKGROUND: Using questionnaires to assess children's residential exposure to environmental tobacco smoke (ETS) may result in misclassification from recall and response bias. Questionnaire data have frequently been validated against urinary cotinine measurements, but rarely against actual measurements of residential air nicotine. OBJECTIVE: To compare questionnaire reported smoking with air nicotine concentrations in a large population of children and with urinary cotinine levels in a subpopulation; and to assess the potential impact of the symptom status of the children on the agreement between different measures of exposure. METHODS: The authors assessed residential exposure to ETS in 347 German, 335 Dutch, and 354 Swedish preschool and schoolchildren by questionnaire and air nicotine measurements, and in a subset of 307 German children by urinary cotinine measurements. They then compared the different measures of ETS exposure. RESULTS: In all countries, air nicotine concentrations increased with increasing questionnaire reported smoking in a dose-response fashion. Specificity and negative predictive values of questionnaire reports for nicotine concentrations were excellent. Sensitivity and positive predictive values were moderate to good. Excluding occasional smokers, the overall percentage of homes misclassified was 6.9%, 6.7%, and 5.1% in Germany, the Netherlands, and Sweden, respectively. Similar results were found for the agreement of urinary cotinine concentrations with questionnaire reports and air nicotine levels. There was no indication of underreporting by parents of symptomatic children. CONCLUSION: Despite some misclassification, questionnaire reports are an inexpensive and valid estimate of residential ETS exposure among preschool and school children.

Adult↗

PubMed2006

[The dangers to health of fine dust particles in the air].

Many scientific studies have been published that connect all kinds of toxicological characteristics offine dust particles, measured in vitro, with lung damage parameters both in animals and humans. These studies do not provide an unequivocal picture on the mechanisms that are responsible for the perceived connection between exposure to fine dust and the degree of illness and death. Without connecting to specific sources of air pollution, this type of study moreover, is only of limited value for drawing up control policy. Even if one or more responsible properties could be determined, it is still unlikely that these would be translated into a standard for permitted levels of concentration in the open air. It is far more likely that such insight will be used for specific source policy aimed at tackling the sources that contribute the most to the harmfulness of the mixture of air pollution.

Air Pollutants↗

PubMed2006

Repeated measurements of mite and pet allergen levels in house dust over a time period of 8 years.

BACKGROUND: Studies of the association between indoor allergen exposure and the development of allergic diseases have often measured allergen exposure at one point in time. OBJECTIVE: We investigated the variability of house dust mite (Der p 1, Der f 1) and cat (Fel d 1) allergen in Dutch homes over a period of 8 years. METHODS: Data were obtained in the Dutch PIAMA birth cohort study. Dust from the child's mattress, the parents' mattress and the living room floor was collected at four points in time, when the child was 3 months, 4, 6 and 8 years old. Dust samples were analysed for Der p 1, Der f 1 and Fel d 1 by sandwich enzyme immuno assay. RESULTS: Mite allergen concentrations for the child's mattress, the parents' mattress and the living room floor were moderately correlated between time-points. Agreement was better for cat allergen. For Der p 1 and Der f 1 on the child's mattress, the within-home variance was close to or smaller than the between-home variance in most cases. For Fel d 1, the within-home variance was almost always smaller than the between-home variance. Results were similar for allergen levels expressed per gram of dust and allergen levels expressed per square metre of the sampled surface. Variance ratios were smaller when samples were taken at shorter time intervals than at longer time intervals. CONCLUSION: Over a period of 4 years, mite and cat allergens measured in house dust are sufficiently stable to use single measurements with confidence in epidemiological studies. The within-home variance was larger when samples were taken 8 years apart so that over such long periods, repetition of sampling is recommended.

Air Pollution, Indoor↗

PubMed2006

Allergic diseases and atopic sensitization in children related to farming and anthroposophic lifestyle--the PARSIFAL study.

BACKGROUND: The prevalence of allergic diseases has increased rapidly in recent decades, particularly in children. For adequate prevention it is important not only to identify risk factors, but also possible protective factors. The aim of this study was to compare the prevalence of allergic diseases and sensitization between farm children, children in anthroposophic families, and reference children, with the aim to identify factors that may protect against allergic disease. METHODS: The study was of cross-sectional design and included 14,893 children, aged 5-13 years, from farm families, anthroposophic families (recruited from Steiner schools) and reference children in Austria, Germany, The Netherlands, Sweden and Switzerland. A detailed questionnaire was completed and allergen-specific IgE was measured in blood. RESULTS: Growing up on a farm was found to have a protective effect against all outcomes studied, both self-reported, such as rhinoconjunctivitis, wheezing, atopic eczema and asthma and sensitization (allergen specific IgE > or = 0.35 kU/l). The adjusted odds ratio (OR) for current rhinoconjunctivitis symptoms was 0.50 (95% confidence interval (CI) 0.38-0.65) and for atopic sensitization 0.53 (95% CI 0.42-0.67) for the farm children compared to their references. The prevalence of allergic symptoms and sensitization was also lower among Steiner school children compared to reference children, but the difference was less pronounced and not as consistent between countries, adjusted OR for current rhinoconjunctivitis symptoms was 0.69 (95% CI 0.56-0.86) and for atopic sensitization 0.73 (95% CI 0.58-0.92). CONCLUSIONS: This study indicates that growing up on a farm, and to a lesser extent leading an anthroposophic life style may confer protection from both sensitization and allergic diseases in childhood.

Adolescent↗

PubMed2006

European birth cohort studies on asthma and atopic diseases: I. Comparison of study designs -- a GALEN initiative.

BACKGROUND: The reasons for the rise in asthma and allergies remain unclear. To identify risk or protective factors, it is essential to carry out longitudinal epidemiological studies, preferably birth cohort studies. In Europe, several birth cohort studies on asthma and atopic diseases have been initiated over the last two decades. AIM: One of the work packages within the Global Allergy and Asthma European Network (GA(2)LEN) project was designed to identify and compare European birth cohorts on asthma and atopic diseases. The present review (part I) describes their objectives, study settings, recruitment process and follow-up rates. A subsequent review (part II) will compare outcome and exposure parameters. METHODS: For each birth cohort, we collected detailed information regarding recruitment process, study setting, baseline data (pregnancy, birth, parents/siblings) as well as follow-up rates, outcome and exposure parameters at each time point. RESULTS: We identified and assessed 18 European birth cohorts on asthma, allergic rhinitis and eczema. Six of these studies also focused on food allergies. The birth cohorts were mostly initiated in the 1990s with predominantly urban/metropolitan settings. Many studies were able to maintain high follow-up rates, even after five or more years. CONCLUSIONS: Due to the unique cooperation within the GA(2)LEN project a common database was established containing study characteristics of European birth cohorts on asthma and atopic diseases. This can be used as a basis for evaluating the possibility to pool data and perform meta-analyses, as well as to recommend criteria for conducting future birth cohorts.

Adolescent↗

PubMed2006

Gas cooking, kitchen ventilation, and asthma, allergic symptoms and sensitization in young children--the PIAMA study.

BACKGROUND: Several studies reported inconsistent associations between using gas for cooking and respiratory symptoms or lung function in children. Kitchen ventilation characteristics may modify the relationship between gas cooking and respiratory health. The aim of this study was to investigate the effect of kitchen ventilation (while cooking) on the relationship between gas cooking, combustion product dispersal, and respiratory and allergic outcomes in children. METHODS: Data on respiratory and allergic symptoms and diagnoses were collected by yearly questionnaires in a population of over 3000 children participating in a birth cohort study on development of allergy and asthma. At 4 years of age, a sub-sample of 647 children provided blood samples for antibody testing. Data on gas cooking and kitchen ventilation were collected when the children were 5 years old. Based on these data a model was constructed to determine the chance of accumulation of combustion products (CACP) in the kitchen. RESULTS: No relationship was found between gas cooking and any of the respiratory or allergy outcomes except nasal symptoms. The overall results did not change when the 'CACP' was used as exposure variable instead, while the association for nasal symptoms decreased to borderline significance. CONCLUSION: Our results suggest that gas cooking per se is associated with nasal symptoms in young children and not with the other respiratory symptoms that were investigated. Taking kitchen ventilation characteristics into account did not lead to different conclusions in this population where, according to the classification system, the majority of households using gas for cooking have insufficient kitchen ventilation.

Air Pollution, Indoor↗

PubMed2006

Nonlinear relations between house dust mite allergen levels and mite sensitization in farm and nonfarm children.

BACKGROUND: Low sensitization rates to common allergens have been observed in farm children, which might be due to high exposure to microbial agents. It is not known how microbial agents modify the association between specific allergen exposure and sensitization. OBJECTIVE: To examine the relations between house dust mite allergen exposure and mite sensitization in farm and nonfarm children and to assess the effects of microbial agents levels on this association. METHODS: Major mite allergens of Dermatophagoides pteronyssinus (Der p 1) and Dermatophagoides farinae (Der f 1), endotoxin, beta(1,3)-glucans and fungal extracellular polysaccharides were measured in mattress dust of 402 children participating in a cross-sectional study in five European countries. Mite allergen (Der p 1 + Der f 1) levels were divided into tertiles with cut-offs 1.4 and 10.4 microg/g. Sensitization was assessed by measurement of allergen-specific immunoglobulin E against house dust mite. RESULTS: Prevalence ratios of mite sensitization for medium and high when compared with low mite allergen levels were 3.1 [1.7-5.7] and 1.4 [0.7-2.8] respectively. Highest mite sensitization rates at intermediate exposure levels were consistently observed across country (except for Sweden) and in both farm and nonfarm children. The shape of the dose-response curve was similar for above and below median mattress microbial agent levels, but the 'sensitization peak' appeared to be lower for above median levels. CONCLUSIONS: Our data suggest a bell-shaped dose-response relationship between mite allergen exposure and sensitization to mite allergens. In populations with high microbial agent levels and low sensitization rates, the curve is shifted down.

Adolescent↗

PubMed2006

European birth cohort studies on asthma and atopic diseases: II. Comparison of outcomes and exposures--a GA2LEN initiative.

BACKGROUND: The Global Allergy and Asthma European Network (GA2LEN) is a consortium of 26 leading European research centres committed to establish a European research area of excellence in the field of allergy and asthma. AIM: One of the GA2LEN work packages was designed to identify and compare the existing European birth cohort studies on asthma and atopic diseases. The present review compares their subjective and objective outcomes as well as exposure variables. METHODS: A common database was established to assess study characteristics of observational birth cohort studies designed to examine asthma and atopic diseases. Data were collected by visiting most of the participating research teams and interviewing all relevant study personnel. For each study, the type of objective/subjective outcome parameters and potentially influential factors were recorded precisely for every time point during follow-up. RESULTS: Eighteen birth cohort studies on asthma and atopic diseases were identified in eight European countries. Thirteen studies collected data on specific immunoglobulin E (IgE) to various inhalant and food allergens, whereas 12 performed skin prick tests (many at several time points during follow up). Several studies measured lung function, but across the cohorts no comparable standard procedures were used. For subjective evaluation of asthma and allergic rhinitis most studies applied the ISAAC questionnaire (sometimes modified), whereas the assessment of eczema was rather heterogeneous across the studies. CONCLUSION: This GA2LEN initiative established a unique common database of 18 European birth cohorts on asthma and atopic diseases. For selected cohorts, it seems that pooling data and performing common analyses may be possible to examine associations between certain exposure variables (e.g. pet ownership, tobacco smoke exposure and day-care) and selected outcome measures for atopy, asthma or allergic rhinitis (e.g. sensitization assessed by IgE or skin prick tests, doctor's diagnosis of asthma, parental perception regarding asthma/wheezing or hay fever symptoms).

Asthma↗

PubMed2006

Gas cooking, kitchen ventilation, and exposure to combustion products.

We evaluated a questionnaire-based system for classifying homes into groups with distinctly different chances of accumulating combustion products from cooking appliances. The system was based on questions about type of cooking appliance, type and use of ventilation provisions, and kitchen size. Real-time measurements were made of CO, CO(2), temperature, and water vapor, and passive sampling was performed of nitrogen oxides, over a week-long period in 74 kitchens. During the measurements, inhabitants kept a diary to record appliance use time and use of ventilation provisions. The questionnaire-based and diary-based home classifications for the 'Chance of Accumulation of Combustion Products' (CACP) turned out to agree fairly well. For CO(2) as well as for CO a significant difference between the 'high' and 'low' CACP groups was found for the mean accumulation in the kitchen during cooking of the combustion generated concentrations. These facts are considered to be important experimental evidence of the CACP stratification being valid for our study population. In the homes studied, NO(2) as well as CO concentrations were found to be lower compared with previous studies in The Netherlands. Practical Implications Previous studies on indoor combustion product dispersal conducted in the early- to mid-1980s in the Netherlands showed much higher NO(2) and CO concentrations than the present study. Apparently, the removal of combustion products formed during cooking is more efficient in the (mostly newer) homes that we studied than in the homes studied in the early- to mid-1980s. More detailed knowledge of kitchen situations is needed to improve the CACP model. Future studies can achieve this by using questionnaires on the kitchen situation, diaries and real-time measurements of the combustion products under consideration.

Air Pollution, Indoor↗

PubMed2006

Exposure to microbial components and allergens in population studies: a comparison of two house dust collection methods applied by participants and fieldworkers.

Dust collection by study participants instead of fieldworkers would be a practical and cost-effective alternative in large-scale population studies estimating exposure to indoor allergens and microbial agents. We aimed to compare dust weights and biological agent levels in house dust samples taken by study participants with nylon socks, with those in samples taken by fieldworkers using the sampling nozzle of the Allergology Laboratory Copenhagen (ALK). In homes of 216 children, parents and fieldworkers collected house dust within the same year. Dust samples were analyzed for levels of allergens, endotoxin, (1-->3)-beta-D-glucans and fungal extracellular polysaccharides (EPS). Socks appeared to yield less dust from mattresses at relatively low dust amounts and more dust at high dust amounts than ALK samples. Correlations between the methods ranged from 0.47-0.64 for microbial agents and 0.64-0.87 for mite and pet allergens. Cat allergen levels were two-fold lower and endotoxin levels three-fold higher in socks than in ALK samples. Levels of allergens and microbial agents in sock samples taken by study participants are moderately to highly correlated to levels in ALK samples taken by fieldworkers. Absolute levels may differ, probably because of differences in the method rather than in the person who performed the sampling. Practical Implications Dust collection by participants is a reliable and practical option for allergen and microbial agent exposure assessment. Absolute levels of biological agents are not (always) comparable between studies using different dust collection methods, even when expressed per gram dust, because of potential differences in particle-size constitution of the collected dust.

Air Pollutants↗

PubMed2005

Diet and asthma in Dutch school children (ISAAC-2).

BACKGROUND: The rise in the prevalence of asthma in western societies may be related to changed dietary habits. Epidemiological studies in children have shown inverse associations of asthma related outcomes with intake of fruits, vegetables, dairy and whole grain products, and fish. In contrast to most previous studies, we used both questionnaire and clinical data to define asthma. METHODS: Intake of the abovementioned foods was studied in relation to asthma in 598 Dutch children aged 8-13 years. Dietary intake was estimated using a parent completed semi-quantitative food frequency questionnaire. Current wheeze and current asthma were defined based on questionnaire data. More complex end points were defined using information on bronchial hyperresponsiveness (BHR) and atopic sensitisation as well. Linear associations were studied using logistic regression analysis and odds ratios presented for the highest versus the lowest tertile of intake. In the final models, adjustments were made for maternal educational level, foreign descent, and total energy intake. RESULTS: The intake of whole grain products and of fish was inversely associated with asthma. Adjusted odds ratios for the independent associations with whole grains and fish were 0.46 (95% CI 0.19 to 1.10) and 0.34 (95% CI 0.13 to 0.85) for current asthma and 0.28 (95% CI 0.08 to 0.99) and 0.12 (95% CI 0.02 to 0.66) for atopic asthma with BHR. Similar results were observed for current wheeze and atopic wheeze with BHR. Intake of (citrus) fruits, vegetables, and dairy products showed no clear associations with asthma end points. CONCLUSIONS: Our findings suggest that a high intake of whole grain products and fish may have a protective effect against asthma in children.

Adolescent↗

PubMed2005

Validation of questions on asthma and wheeze in farming and anthroposophic children.

BACKGROUND: In most epidemiological surveys the estimated prevalence of asthma is based on questionnaire responses, which may depend on the individual's perception as well as medical consulting habits in a given population. Therefore, measurement of bronchial hyper-responsiveness as a key feature of asthma has been suggested as an objective parameter for asthma. OBJECTIVE: The aim of the present study was to validate questionnaire responses on asthma and wheeze against bronchial response to hypertonic saline (HS) (4.5%) in populations previously shown to have a lower prevalence of asthma and allergies: farmers' children and children from anthroposophic families. METHODS: Children whose parents had completed a written questionnaire in the cross-sectional PARSIFAL-study were drawn from the following four subgroups: 'farm children' (n=183), 'farm reference children' (n=173), 'Steiner schoolchildren' (n=243) and 'Steiner reference children' (n=179). Overall, 319 children with wheeze in the last 12 months and 459 children without wheeze in the last 12 months performed an HS challenge. RESULTS: Odds ratios, sensitivity, specificity, likelihood ratios and measures of association did not differ significantly between the four subgroups. The correlation between the bronchial response to HS and wheeze and asthma questions was moderate and similar for farm children, farm reference children, Steiner schoolchildren and Steiner reference children (kappa for 'wheeze': 0.25, 0.33, 0.31, 0.35, respectively, P=0.754, kappa for 'doctor's diagnosis of asthma': 0.33, 0.19, 0.33, 032, respectively, P=0.499). CONCLUSION: The findings from this study suggest that the reliabilitiy of questionnaire responses on asthma and wheeze is comparable between farmers' children, children raised in families with anthroposophic lifestyle and their respective peers.

Adolescent↗

PubMed2005

Bacterial and fungal agents in house dust and wheeze in children: the PARSIFAL study.

BACKGROUND: Growing up on a farm and an anthroposophic lifestyle are associated with a lower prevalence of allergic diseases in childhood. This might be related to increased inhalatory exposure to microbial agents. OBJECTIVE: To assess the association between microbial agents in house dust and atopic wheeze in farm children, Steiner school children and reference children. METHODS: Levels of bacterial endotoxin, fungal beta(1,3)-glucans and fungal extracellular polysaccharides (EPS) in mattress and living room floor dust were measured in a population of 270 atopic (=Phadiatop-positive) children with self-reported wheezing, including 168 current atopic wheezers, and 441 non-atopic, non-symptomatic controls. These children were selected from a cross-sectional study in five European countries. RESULTS: In the study population as a whole, average levels of mattress dust endotoxin, EPS and glucans were slightly (1.1-1.2-fold; P<0.10) higher in control children than in atopic wheezers. Atopic wheeze was related to mattress levels of endotoxin, EPS and glucans in farm and farm-reference children. However, when adjusting for group (farm vs. farm-reference children), the associations became non-significant whereas the group effect remained. No associations between atopic wheeze and microbial agents were observed in Steiner and Steiner-reference children. For current atopic wheeze, the farm effect became non-significant after adjustment for microbial agent levels. CONCLUSION: Not only bacterial endotoxin but also mould components might offer some protection against atopic wheeze in children. However, the protective effect of being raised on a farm was largely unexplained by the mattress microbial agent levels measured in this study.

Adolescent↗

PubMed2005

Early childhood environment related to microbial exposure and the occurrence of atopic disease at school age.

BACKGROUND: There is a growing body of evidence that the early childhood environment with respect to day care attendance, older siblings, pet ownership, and early life airway infections may protect from developing atopic disease. Few studies have distinguished between atopic sensitization and symptoms, and none have evaluated independent contributions for all of these different environmental conditions. OBJECTIVE: Examine independent effects on atopic sensitization and symptoms of day care attendance, older siblings, pet ownership, and early infancy's airway disease. METHODS: A cross-sectional survey among 8-13-year-old school children with complete data for 1555 children. RESULTS: After adjustment for confounders, atopic sensitization occurred less frequently in children that had attended a day care centre (OR: 0.73, 95% CI: 0.55-0.98) or had a cat or dog before 2 years of age (OR: 0.78, 95% CI: 0.61-0.99). Having older siblings yielded a nonsignificant trend towards protection (OR: 0.88, 95% CI: 0.70-1.11). For symptoms, there was no relation with having older sibs, day care attendance and pet ownership, although there was a trend towards protection for the combination of atopy and symptoms. In contrast, children with doctors' treated airway disease before age 2, more frequently reported recent symptoms of wheeze, asthma, rhinitis, or dermatitis (all P < 0.05). CONCLUSION: Early life environmental exposure to day care, or pets may protect against atopic sensitization. Protection against symptoms only occurred if atopic sensitization was present as well.

Air Microbiology↗

PubMed2005

Bacterial and fungal components in house dust of farm children, Rudolf Steiner school children and reference children--the PARSIFAL Study.

BACKGROUND: Growing up on a farm and an anthroposophic lifestyle are associated with a lower prevalence of allergic diseases in childhood. It has been suggested that the enhanced exposure to endotoxin is an important protective factor of farm environments. Little is known about exposure to other microbial components on farms and exposure in anthroposophic families. OBJECTIVE: To assess the levels and determinants of bacterial endotoxin, mould beta(1,3)-glucans and fungal extracellular polysaccharides (EPS) in house dust of farm children, Steiner school children and reference children. METHODS: Mattress and living room dust was collected in the homes of 229 farm children, 122 Steiner children and 60 and 67 of their respective reference children in five European countries. Stable dust was collected as well. All samples were analysed in one central laboratory. Determinants were assessed by questionnaire. RESULTS: Levels of endotoxin, EPS and glucans per gram of house dust in farm homes were 1.2- to 3.2-fold higher than levels in reference homes. For Steiner children, 1.1- to 1.6-fold higher levels were observed compared with their reference children. These differences were consistently found across countries, although mean levels varied considerably. Differences between groups and between countries were also significant after adjustment for home and family characteristics. CONCLUSION: Farm children are not only consistently exposed to higher levels of endotoxin, but also to higher levels of mould components. Steiner school children may also be exposed to higher levels of microbial agents, but differences with reference children are much less pronounced than for farm children. Further analyses are, however, required to assess the association between exposure to these various microbial agents and allergic and airway diseases in the PARSIFAL population.

Agriculture↗

PubMed2005

Cesarean delivery and cow milk allergy/intolerance.

The present study provides support for a positive association between cesarean delivery and persistent cow milk allergy/cow's milk intolerance. Correspondingly, a negative association was seen between cesarean delivery and early outgrown cow milk allergy/intolerance. A possible explanation is that cesarean delivery, rather than increasing the overall risk of food allergy, increases the risk of persistency of disease among food allergic children.

Cesarean Section↗

PubMed2005

Are house dust mite allergen levels influenced by cold winter weather?

BACKGROUND: Moisture is vitally important for house dust mites and they cannot survive in cold or hot-dry climates. AIMS OF THE STUDY: To investigate the influence of two extraordinarily cold and dry winters in 1995/1996 and 1996/1997 on house dust mite levels in German homes. METHODS: Dust samples were collected between June 1995 and December 2001 on the mattresses of 655 adults and 454 schoolchildren living in five different areas of Germany. We compared house dust mite allergen Dermatophagoides pteronyssinus (Der p 1) levels before and during the winters of 1995/1996 and 1996/1997 with levels after these winters. RESULTS: D. pteronyssinus (Der p 1) levels in samples taken after the cold winters of 1995/1996 and 1996/1997 were approximately two times lower than Der p 1 levels in dust samples collected before or during these respective winters (Geometric means: Erfurt 89 vs 33 ng/g; Hamburg 333 vs 219 ng/g; Bitterfeld, Hettstedt, and Zerbst 296 vs 180 ng/g). Except for Hamburg, the decrease in Der p 1 levels was statistically significant. D. pteronyssinus levels measured in dust samples collected in 2001 (i.e. 3 years after the two cold winters) show a statistically non-significant increase (Geometric means: Erfurt 33 vs 39 ng/g; Hamburg 219 vs 317 ng/g), suggesting that it may take a long time for mite allergen levels to increase again after a sudden decrease. CONCLUSION: We conclude that Der p 1 levels in German mattress dust samples have been approximately reduced by a factor of three to four by the two consecutive cold winters of 1995/1996 and 1996/1997.

Adult↗

PubMed2005

La mano de DIOS...was the PIAMA intervention study intervened upon?

The PIAMA study evaluates whether application of mite impermeable mattress covers reduces exposure to mite allergen sufficiently to reduce the incidence of asthma and mite allergy. The study started in 1996. Baseline measurements of mite allergen levels were conducted on mattresses of newborn children and their parents, mostly in 1997. Mite allergen levels were surprisingly low in this study compared with previous studies among school children and infants. Mite allergen levels were measured again on mattresses in the PIAMA study in the years 2000/2001 when the children were 4 years old, and in a new study among 6-12 year old school children conducted in the fall of 2001. Data on winter climate were collected as well. In the winters of 1995/1996 and 1996/1997, which preceded and coincided with the PIAMA baseline measurements, temperatures had been extremely low, and precipitation had been extremely low as well. It is likely that these unusual winter weather conditions affected the baseline allergen levels in the PIAMA study so that the effect of the planned intervention (mite impermeable mattress covers) was considerably smaller than it could have been.

Antigens, Dermatophagoides↗