Dust Mite Allergen Concentrations Research Articles

Role of ventilation and cleaning for controlling house dust mite allergen infestation: A study on associations of house dust mite allergen concentrations with home environment and life styles in Tianjin area, China.

House dust mites produce well-known allergens for asthma and allergy among children. To study house dust mite allergen exposure level in northeast China and characterize its association with indoor environmental factors and cleaning habits, we inspected 399 homes in Tianjin area and collected dust from mattresses. Dermatophagoides farinae (Der f) and Dermatophagoides pteronyssinus (Der p) were detected by the enzyme-linked immunosorbent assay (ELISA) method. The medians of total allergen concentrations for spring, summer, autumn, and winter were 524 ng/g, 351 ng/g, 1022 ng/g, and 1010 ng/g. High indoor air relative humidity (RH), low air change rate, indoor dampness, and frequent changing of quilt cover/bedsheet/pillow case were significantly associated with high house dust mite allergen concentration (relative risk [RR]: RH, 1.18-1.34; air change rate, 0.97-1.00; dampness, 2.92-3.83; changing quilt cover/bedsheet/pillow case, 0.66-0.75). The decrease in the absolute humidity gradient between indoors and outdoors that occurs with increased air change rate may explain why a high ventilation reduces house dust mite allergen concentration. The findings of this study show the importance of ventilation and cleaning for controlling house dust mite allergens. We found that the decrease in additional absolute humidity (e.g., humidity indoor -humidity outdoor ) with increased air change rate may be the main reason that a high ventilation rate reduces house dust mite allergen concentration. Ventilation and cleaning should be both considered for creating a healthy home environment.

Impact of environmental factors and bacterial interactions on dust mite allergens in different indoor dust

Indoor dust is the main carrier of indoor pollutants, especially dust mite allergens and bacteria, they can trigger asthma, rhinitis, eczema and other allergic diseases. However, the interactions between dust mite allergens and bacterial communities in different types of indoor dust are not clear. The study focused on particulate and flocculent fibrous dust, explored the concentrations of Der p 1 (Dermatophagoides pteronyssinus) and Der f 1 (D. farinae) in 46 households in Changchun and their environmental influences, characterized the bacterial communities by high-throughput sequencing, and the interactions between Der p 1, Der f 1 and bacterial communities were explored. The results showed that Der p 1 and Der f 1 tended to accumulate more in flocculent fibrous dust, and Der p 1 predominated in the indoor dust samples. The floor height, years of housing occupancy and the living areas all affected the concentrations of dust mite allergens. In bacterial community, Proteobacteria, Firmicutes and Actinobacteria were leading phyla in the two types of dust. Kocuria, Blastococcus and Massilia were dominating genera in particulate dust and Acinetobacter, Lactobacillus, Corynebacterium_1 were dominating genera in flocculent fibrous dust. The overall diversity and species richness of bacteria in particulate dust were significantly higher than those in flocculent dust (p < 0.001). The living area was an important environmental factor affecting the bacterial community in flocculent fibrous dust (p < 0.01). The interaction between the relative abundance of Proteobacteria, Firmicutes and Actinobacteria and dust mite allergen concentrations significantly differed between the two dust types, indicating that bacteria could be used both as food and to establish symbiotic relationships with household dust mites (HDMs) hosts and provide nutrition.

Allergic Rhinitis Improvement in Asthmatic Children After Using Acaricidal Bait: A Randomized, Double-Blind, Cross-Placebo Study

Objective: This study aimed to evaluate the effects of acaricidal bait use on the house dust mite (HDM) allergen concentration and occurrence of allergic rhinitis (AR) and asthma symptoms in children sensitized to HDMs.Study Design: Sixty-six children (3–12 years old) with AR and asthma sensitized to HDMs were randomly assigned to receive an acaricidal bait intervention for 8 weeks and a placebo intervention for 8 weeks separated by a 4-week washout period. The visual analog scale (VAS) score, rhinitis control assessment test (RCAT) score, rhinoconjunctivitis quality of life questionnaire (RQLQ) score, asthma control questionnaire-5 (ACQ-5) score and HDM allergen levels were monitored.Results: HDM allergen levels were significantly decreased after 8 weeks (Δder p2+f2 2.282 (3.516) μg/g vs. 0.147 (0.25) μg/g, P < 0.05) in the acaricidal bait group compared with the placebo group. The VAS, RCAT and RQLQ scores in the acaricidal bait group were also significantly improved (ΔVAS 7.5 (16) vs. 3 (18), P < 0.05; ΔRCAT−3 (5) vs. 0 (7), P < 0.05; ΔRQLQ 4.5 (8) vs. 1 (8), P < 0.05), but the ACQ-5 score did not improve (ΔACQ-5 0.2 (0.4) vs. 0 (0.65), P > 0.05).Conclusion: Acaricidal bait reduced HDM exposure and improved rhinitis symptoms. This trial is registered at www.chictr.org.cn.

Is there an association between indoor allergens and the severity of atopic dermatitis?

Atopic dermatitis (AD) is a multifactorial inflammatory skin disease with frequent hypersensitivity to allergens. However, the role of exposure to indoor allergens on AD severity is unclear. Children aged 0-17 years with active AD from central Chile were recruited; disease severity was evaluated with SCORAD and POEM scores. A home environment survey was applied to parents. Bedroom dust samples were collected for all subjects and analyzed by multiplex assay to quantify dust mite (Der p1, Der f1), dog (Can f1), cat (Fel d1), and alternaria alternata (Alt a1) allergens. Twenty-five children aged 3.9 ± 3.8 years were included. Fifty-two percent were female. Mean SCORAD was 29 ± 14 (range 11-61), and mean POEM was 10.7 ± 6.2. No direct association was found between tobacco exposure, pet ownership, aerosol use, visible dust, or home carpets/rugs with SCORAD (all P > 0.05). Dust samples from all homes had Can f1 and Fel d1 allergens, regardless of pet ownership. Homes that had indoor dogs or cats had significantly higher amounts of these allergens (P < 0.001). Forty percent of homes had dust mite allergens, and none had alternaria alternata. Children with AD living in homes with elevated dust mite and animal dander allergen concentrations had higher SCORAD than those from homes with low allergen concentrations (40 ± 13 vs. 26 ± 13, P = 0.025). High concentrations of indoor allergens may influence AD severity in children. Further studies assessing indoor allergens and allergen sensitization are warranted to fully evaluate the role of indoor allergens on AD.

Primary Paediatric Bronchial Airway Epithelial Cell in Vitro Responses to Environmental Exposures.

The bronchial airway epithelial cell (BAEC) is the site for initial encounters between inhaled environmental factors and the lower respiratory system. Our hypothesis was that release of pro inflammatory interleukins (IL)-6 and IL-8 from primary BAEC cultured from children will be increased after in vitro exposure to common environmental factors. Primary BAEC were obtained from children undergoing clinically indicated routine general anaesthetic procedures. Cells were exposed to three different concentrations of lipopolysaccharide (LPS) or house dust mite allergen (HDM) or particulates extracted from side stream cigarette smoke (SSCS). BAEC were obtained from 24 children (mean age 7.0 years) and exposed to stimuli. Compared with the negative control, there was an increase in IL-6 and IL-8 release after exposure to HDM (p ≤ 0.001 for both comparisons). There was reduced IL-6 after higher compared to lower SSCS exposure (p = 0.023). There was no change in BAEC release of IL-6 or IL-8 after LPS exposure. BAEC from children are able to recognise and respond in vitro with enhanced pro inflammatory mediator secretion to some inhaled exposures.

No Concentration Decrease of House Dust Mite Allergens With Rising Altitude in Alpine Regions.

PurposeSeveral studies over the past 4 decades have indicated a significant reduction in house dust mite (HDM) and HDM allergen concentration in areas higher than 1,500 m above sea level. These have served as basis of allergen avoidance therapies for HDM allergy and asthma. However, modern construction techniques used in the insulation, heating, and glazing of buildings as well as global warming have changed the environmental parameters for HDM living conditions. The present study revisits the paradigm of decreasing HDM allergen concentrations with increasing altitude in the alpine region of Germany and Austria.MethodsA total of 122 dust samples from different abodes (hotels, privates and mountain huts) at different altitudes (400-2,600 m) were taken, and concentrations of HDM allergens were analyzed. Humidity and temperature conditions, and numerous indoor environmental parameters such as fine dust, type of flooring, age of building, and frequency of cleaning were determined.ResultsHDM allergen concentrations did not significantly change with increasing altitude or relative humidity. At the level of indoor parameters, correlations could be found for different flooring types and the concentration of HDM allergens.ConclusionsIn contrast to the widespread view of the relationship between altitude and HDM allergen concentrations, clinically relevant concentrations of HDM allergens could be detected in high-lying alpine regions in Austria and Germany. These results indicate that improvement in conditions of asthmatic patients sensitized against HDMs during a stay at high altitude can no longer be ascribed to decreased levels of HDM allergens, instead, other mechanisms may trigger the beneficial effect.

Mold populations and dust mite allergen concentrations in house dust samples from across Puerto Rico

Lifetime childhood asthma prevalence (LCAP) percentages in Puerto Rico Health Regions (HR) are substantially higher in northeastern vs. southwestern HR. Higher average relative humidity in the northeast might promote mold and mite exposures and possibly asthma prevalence. To test this hypothesis, mold contamination, Environmental Relative Moldiness Index (ERMI) values were measured in floor dust (n = 26) and dust mite allergen concentrations in bed dust (n = 14). For this analysis, the eight HR were divided into those with LCAP > 30 % (n = 3) and < 30 % (n = 5). The average ERMI value was significantly greater (Wilcoxon Rank Sum, p < 0.001) in high than in low LCAP HR (14.5 vs. 9.3). The dust mite antigens Der p 1, Der f 1, and Blo t 5 were detected in 90 % of bed samples, but the concentrations were not significantly different in high vs. low LCAP HR. Mold exposures might partially explain the differences in LCAP HR in Puerto Rico.

The effects of a newsletter on bedding control on house dust mite allergen concentrations in childcare centers in Korea.

ObjectivesBedding in childcare centers (CCCs) can hold house dust mite (HDM) allergens. This study examined whether HDM allergen levels can be reduced through the distribution of an educational newsletter on bedding control to parents of CCC children in Korea.MethodsAll 38 CCCs were measured for Der 1 (sum of Der f 1 and Der p 1) concentrations on classroom floors and bedding before the intervention. Educational newsletters on children’s bedding control were sent to 21 CCCs by mail, and teachers were asked to distribute the newsletters to the parents of the children (intervention group). The remaining 17 CCCs were not sent newsletters (control group). The measurement of Der 1 concentrations in 38 CCCs was repeated after the intervention. Dust samples were collected with a vacuum cleaner and analyzed using enzyme-linked immunosorbent assay methods.ResultsThe Der 1 concentrations on the bedding were significantly higher than those on the floors in 38 CCCs at baseline (p<0.05). Although changes of the Der 1 concentrations for the control group (n=17) were not significant, Der 1 concentrations for the intervention group (n=21) decreased significantly from 2077.9 ng/g dust to 963.5 ng/g dust on the floors and from 3683.9 ng/g dust to 610.4 ng/g dust on bedding (p<0.05).ConclusionsThe distribution of educational newsletters on bedding control to parents may be an effective means of controlling HDMs in CCCs.

IgE antibodies and urinary trimethylarsine oxide accounted for 1-7% population attributable risks for eczema in adults: USA NHANES 2005-2006.

Population attributable risks from serum IgE and dust miteallergen concentrations and environmental chemicals for eczema are unclear. Therefore, it was aimed to examine serum IgE and allergen concentrations and environmental chemicals for eczema in adults and to calculate population attributable risks in a national and population-based setting. Data retrieved from the National Health and Nutrition Examination Survey, 2005-2006, was analyzed. Information on demographics and self-reported ever eczema was obtained by household interview. Bloods and urines (sub-sample) were also collected during the interview. Adults aged 20-85 were included. Statistical analyses were using chi-square test, t test, survey-weighted logistic regression modeling, and population attributable risk (PAR) estimation. Of all the included American adults (n = 4979), 310 (6.2%) reported ever eczema. Moreover, more eczema cases were observed in female adults but fewer cases in people born in Mexico. There were no significant associations observed between commonly known biomarkers (including vitamin D) and eczema or between dust mite allergens and eczema. Serum D. Farinae (PAR 1.0%), D. Pteronyssinus (PAR 1.1%), cat (PAR 1.8%), dog (PAR 1.6%), and muse (PAR 3.2%) IgE antibodies were associated with eczema. Adults with ever eczema were found to have higher levels of urinary trimethylarsine oxide concentrations (PAR 7.0%) but not other speciated arsenic concentrations. There were no clear associations between other environmental chemicals including heavy metals, phthalates, phenols, parabens, pesticides, nitrate, perchlorate, polycyclic hydrocarbons and eczema as well. Elimination of environmental risks might help delay or stop eczema up to 7% in the adult population.

Early-life house dust mite allergens, childhood mite sensitization, and respiratory outcomes.

Exposure to indoor allergens during early life may play a role in the development of the immune system and inception of asthma. To describe the house dust mite (HDM) allergen concentrations in bedroom dust during early life and to evaluate its associations with HDM sensitization, wheezing, and asthma, from birth to school age, in 5 geographically spread European birth cohorts. We included 4334 children from INMA-Menorca (Spain), BAMSE (Sweden), LISAplus and MAS (Germany), and PIAMA-NHS (the Netherlands). Dust samples were collected from bedrooms during early life and analyzed for Dermatophagoides pteronyssinus (Der p1) and Dermatophagoides farinae (Der f1). HDM concentrations were divided into four categories. Sensitization was determined by specific IgE. Wheezing and asthma information up to 8/10 years was collected through questionnaires. We performed mixed-effects logistic regression models and expressed associations as odds ratios with 95% confidence intervals. House dust mite concentrations varied across cohorts. Mean allergen concentrations were highest in INMA-Menorca (geometric mean (GM) Der p1 = 3.3 μg/g) and LISAplus (GM Der f1 = 2.1 μg/g) and lowest in BAMSE (GM Der p1 = 0.1 μg/g, Der f1 = 0.3 μg/g). Moderate and high HDM concentrations were significantly (P-values < 0.05) associated with 50-90% higher prevalence of HDM sensitization. No significant associations were observed with respiratory outcomes. Our study based on geographically spread regions, a large sample size, and a wide range of allergen concentration shows that HDM allergen concentrations vary across regions and that exposure during early life plays a role in the development of allergic sensitization but not in the development of respiratory outcomes.

Decreased FEV1 % in asthmatic adults in Scottish homes with high Environmental Relative Moldiness Index values.

SummaryBackgroundExposures to indoor biological contaminants have been implicated in asthma's aetiology but their effect on lung function is not well quantified.ObjectiveThe aim of this cross‐sectional study of non‐smoking, asthmatic adults in Scotland was to determine the correlation between the results from a standard spirometry test, forced expiratory volume in one‐second percent (FEV 1%), and quantitative estimates of some biological exposures.MethodsA population (n = 55) of non‐smoking, adult asthmatics in Scotland was included in this study and each completed a questionnaire that allowed the determination of the Asthma Control Questionnaire scores (ACQ) and St. George's Respiratory Questionnaire scores (SGRQ), as well as corticosteroid use. Spirometry testing was completed and the pre‐bronchodilator FEV 1% value calculated. At about the same time, floor dust samples were collected in the living room and in the bedroom. These dust samples were analysed for mould contamination, as described by the Environmental Relative Moldiness Index (ERMI) values and by (1, 3)‐β‐D‐glucan concentrations, for endotoxin, and for dust mite, cat, and dog allergen concentrations. The asthmatics' FEV 1% values were tested for correlation (Pearson) to questionnaire‐based estimates of health. Also, each biological exposure was tested for correlation (Pearson) to the FEV 1% values.Results FEV 1% results were correlated with ACQ scores (ρ −0.586, P < 0.001), SGRQ scores (ρ −0.313, P = 0.020), and weakly with corticosteroid use (ρ −0.221, P = 0.105). The ERMI values in the homes (average 5.3) were significantly correlated with FEV 1% values (ρ −0.378, P = 0.004). There was no correlation between FEV 1% and concentrations of endotoxin, (1, 3)‐β‐D‐glucan, or any of the allergens.Conclusion and clinical relevanceAlthough these results do not prove that mould exposures caused the deficit in lung function observed in this study, it might be advisable for asthmatics to avoid high ERMI environments.

서울시 일부 지하철 전동차 객실 시트의 먼지 진드기 알레르겐 농도와 세균 내독소 농도 조사

서울시 일부 지하철 전동차 객실 시트의 먼지 진드기 알레르겐 농도와 세균 내독소 농도 조사

Real-Time Particle Counts Provide a Reliable Indication of Airborne Dust Mite Allergen (Der p 1) Concentration and Ensure Controlled and Safe Exposure for Dust Mite Allergic Patients in an Environmental Exposure Chamber (EEC) Model

Real-Time Particle Counts Provide a Reliable Indication of Airborne Dust Mite Allergen (Der p 1) Concentration and Ensure Controlled and Safe Exposure for Dust Mite Allergic Patients in an Environmental Exposure Chamber (EEC) Model

Use of gelatin filter and BioSampler in detecting airborne H5N1 nucleotides, bacteria and allergens

In this study, the pure influenza A virus (H5N1) nucleotides, dermatophagoides allergens (Der f 1 and Der p 1), and Bacillus subtilis vegetative cells were aerosolized and collected by a Button Aerosol Sampler equipped with gelatin filter and a BioSampler, which were operated at 4 and 12.5 L/min, respectively, for 1–5 min. The collected air samples were analyzed by quantitative polymerase chain reaction (qPCR) and enzyme-linked immuosorbent assay (ELISA). In addition, the performances of the samplers when quantifying total outdoor bacteria were also studied. The cycle threshold (Ct) value for 0.1 fg/μl RNA positive control was observed around 26, and the Ct value for the negative control was about 30. Gelatin filters were shown to report 1-2 times higher nucleotides and B. subtilis concentrations than those obtained by the BioSampler. When sampling outdoor bacteria, both samplers however obtained similar concentration levels ( p-value=0.36). In contrast, the BioSampler reported substantially higher dust mite allergen concentration levels, especially for Der f 1 than the gelatin filters in this study. The sampling time up to 5 min was shown not to have a statistically significant effect on the performance of qPCR when the gelatin filter was used. Such finding was also observed with the performance of ELISA for the sampling time up to 15 min. This study suggests that the bioaerosol sampler, collection medium and analysis methods such as qPCR and ELISA would play overall roles in characterizing airborne biological materials.

Dust Mite Allergen Reduction Study

RATIONALE: Asthmatics are encouraged to employ interventions to reduce exposure to indoor allergens, but often lack objective evidence to confirm the efficacy of their efforts. In-home test kits and education may influence dust mite allergen reduction. METHODS: This randomized controlled trial enrolled 60 households of children aged 5-15 years with parent-reported dust mite allergy and allergen concentrations ≥2μg/g in the child's bedroom. The intervention group (N = 30) received educational materials and in-home dust mite test kits at baseline, 1, 2, 5, and 8 months. The control group (N = 30) received only educational materials. Nonparametric sign tests were performed to determine the likelihood of mite levels decreasing vs. increasing. RESULTS: At baseline and 8 months, 37% and 61% of intervention households, respectively, had dust mite concentrations <2 μg/g and 7% and 4%, respectively, had >10μg/g in bed. At baseline and 8 months, 26% and 74% of intervention households, respectively, had dust mite concentrations <2 μg/g and 7% and 0%, respectively, had >10 μg/g on bedroom floor. Decreased dust mite levels from baseline to months 1, 2, 5 and 8 were statistically significant in floor (p < 0.002) and from baseline to months 2 and 5 in bed (p < 0.02). CONCLUSIONS: There was an increase in the number of tests with dust mite concentrations ≤2 ug/g and a decrease in the number of tests with dust mite concentrations >10 μg/g in the intervention group. Use of in-home test kits along with educational materials reduced dust mite allergen in bedrooms of children with reported dust mite allergy. The study had limited power to test other potential covariates.

Resuspension of indoor aeroallergens and relationship to lung inflammation in asthmatic children

Studies have shown links between the concentration of allergens found in homes and asthma. Inhalation of allergens present in settled residential dust can occur when the dust is resuspended via human activity or air currents. Although previous studies have measured allergen concentrations in homes, the focus has been on the presence of the allergens in settled dust samples. However, the actual inhalation exposure is to airborne allergens. The relationship between the settled dust composition and suspended allergens and endotoxin and the effect of exposure of these aeroallergens to asthmatics are not well understood for species typically present indoors. In this study, settled dust and airborne particulate matter samples were collected in the homes and school classrooms of asthmatic children of ages 9 to 16 and analyzed for endotoxin and allergens including dust mite and cockroach allergen, and dog and cat dander (Der p1, Der f1, Bla g1, Can f1, and Fel d1, respectively). Concentrations of cockroach allergen were below detection limit for all samples. Measurements of the settled dust samples show higher dust mite allergen in bedroom samples than in living room samples. Concentrations of airborne endotoxin and indoor allergens were generally higher in the homes than those measured at school. Within the homes, higher concentrations of airborne allergens and endotoxin were observed in the living rooms compared to the bedrooms. Resuspension rates for endotoxin, dust mite allergen, and, cat and dog dander were estimated in this study. Calculated resuspension rates for cat dander (8.1×10−7±3.5×10−7min−1) and dust mite allergen (2.1×10−6±7.6×10−7min−1and 1.4×10−5±4.6×10−6min−1 for Der p 1 and Der f 1, respectively) were found to be higher than those for dog dander (3.1×10−7±1.3×10−7min−1) and endotoxin (3.6×10−7±1.6×10−7min−1). Markers of asthma inflammation including nitrate in exhaled breath condensate (EBC) and exhaled nitric oxide (eNO), were correlated with the concentrations of dust mite allergen (Der p 1) (Spearman r=0.598; p-value=0.068 for EBC and Spearman r=0.819; p-value=0.007 for eNO) and cat dander (Fel d 1) (Spearman r=0.917; p-value=0.0002 for EBC and Spearman r=0.697; p-value=0.054 for eNO) present in PM10 samples.

Association of pediatric asthma severity with exposure to common household dust allergens

Reducing exposure to household dust inhalant allergens has been proposed as one strategy to reduce asthma. To examine the dose-response relationships and health impact of five common household dust allergens on disease severity, quantified using both symptom frequency and medication use, in atopic and non-atopic asthmatic children. Asthmatic children (N=300) aged 4-12 years were followed for 1 year. Household dust samples from two indoor locations were analyzed for allergens including dust mite (Der p 1, Der f 1), cat (Fel d 1), dog (Can f 1), cockroach (Bla g 1). Daily symptoms and medication use were collected in monthly telephone interviews. Annual disease severity was examined in models including allergens, specific IgE sensitivity and adjusted for age, gender, atopy, ethnicity, and mother's education. Der p 1 house dust mite allergen concentration of 2.0 microg/g or more from the main room and the child's bed was related to increased asthma severity independent of allergic status (respectively, OR 2.93, 95% CI 1.37, 6.30 for 2.0-10.0 microg/g and OR 2.55 95% CI 1.13, 5.73 for 10.0 microg/g). Higher pet allergen levels were associated with greater asthma severity, but only for those sensitized (cat OR 2.41 95% CI 1.19, 4.89; dog OR 2.06 95% CI 1.01, 4.22). Higher levels of Der p 1 and pet allergens were associated with asthma severity, but Der p 1 remained an independent risk factor after accounting for pet allergens and regardless of Der p 1 specific IgE status.

Longitudinal Evaluation of Allergen and Culturable Fungal Concentrations in Inner-City Households

To characterize seasonal variation of three allergens (dust mite, cat, and cockroach) and total culturable fungi and to explore whether residential characteristics were associated with the concentrations of these agents, floor dust was collected from 47 inner-city homes in Minneapolis, Minnesota, over a 1-year period. A longitudinal analysis of allergen and fungal concentrations was carried out using mixed-effect models. Overall, relative humidity was a better predictor of allergen concentrations over time than indoor temperature. Seasonal variation of cat and cockroach allergens was negligible compared with the variability associated with residential characteristics such as race/ethnicity, family income, and the presence of cats. Fungal concentrations showed significant seasonal variation that outweighed the variability associated with residential characteristics. Less than 30% of the dust mite allergen and cockroach allergens concentrations were above limits of detection. Observed cockroach allergen concentrations were higher in Spanish- and Somali-speaking households than in English-speaking households, while English-speaking households had significantly higher cat allergen concentrations compared with the other language groups. The ratios of within-home to between-home variance for total culturable fungi, dust mite, cockroach, and cat allergen concentrations were 2.54, 1.91, 0.55, and 0.24, respectively. This ratio is used to predict the number of repeated measurements of each allergen required to robustly estimate long-term exposure estimates such that exposure misclassification bias is kept within acceptable limits. It is not clear whether repeated measurements of dust mite and cockroach allergens are required for long-term average exposure because of the large fraction of nondetects. It is concluded that a single measurement of cat allergen is a reasonable surrogate for long-term average exposure, since repeated measurements over time were highly correlated. Total culturable fungi will require greater than nine repeated measurements for robust assessment of long-term exposures because of low correlations in fungal measures over time.

Seasonal trends in house dust mite allergen in children’s beds over a 7‐year period

House dust mite (HDM) allergy is closely linked to the expression of asthma and other allergic diseases. Understanding factors influencing variation in allergen may help in controlling allergic disease. The objective of this study was to investigate the effects of seasonal changes in climate, type of bed used in very early childhood and anti-mite interventions on HDM allergen concentration. Participants were enrolled in a randomized-controlled trial of HDM avoidance. Der p 1 was measured in dust samples from children's beds on 13 occasions, from birth to age 5 years, between 1997 and 2004. Bed types were categorized as bassinette, cot or bed. The effects of study month, type of bed and intervention group on HDM allergen concentration were estimated by multiple linear regression. The relation between climatic variables and HDM allergen concentration was investigated using a polynomial distributed lag model. House dust mite allergen concentrations were initially low in cots and bassinettes in 1997/1998, peaked in bassinettes and beds between 1999 and 2001 and then slowly declined during the period 2002/2004. Seasonal fluctuations occurred with minima in summer and two- to threefold higher maxima during late autumn. Allergen peaks were correlated with relative humidity peaks 2 months previously. Seasonal changes in allergen were not affected by the HDM avoidance intervention. House dust mite allergen concentrations in Sydney beds fluctuate approximately two- to threefold on an annual cycle, partly determined by relative humidity, with peaks in late autumn and minima in summer. Fluctuations of this magnitude might be sufficient to influence asthma symptoms.

Early allergen exposure and atopic eczema

The relationship between exposure to indoor aeroallergens in early life and subsequent eczema is unclear. We have previously failed to show any significant associations between early life exposure to house dust mite and cat fur allergens and either sensitization to these allergens or wheeze. We have also previously reported a lower prevalence of parent-reported, doctor-diagnosed eczema by age 2 years for children exposed to higher concentrations of house dust mite, but no other associations with other definitions of eczema or for exposure to cat allergen. To extend the exposure-response analysis of allergen exposure and eczema outcomes measured up to age 8 years, and to investigate the role of other genetic and environmental determinants. A total of 593 children (92 x 4% of those eligible) born to all newly pregnant women attending one of three general practitioner surgeries in Ashford, Kent, were followed from birth to age 8 years. Concentrations of house dust mite and cat allergen were measured in dust samples collected from the home at 8 weeks after birth. The risk of subsequent eczema as defined by the U.K. diagnostic criteria was determined according to different levels (quintiles) of allergen exposure at birth. By age 8 years, 150 (25 x 3%) children had met the diagnostic criteria for eczema at least once. Visible flexural dermatitis was recorded at least once for 129 (28 x 0%). As in other studies, parental allergic history was positively associated with most eczema outcomes, as were higher maternal education and less crowded homes. No clear linear associations between early exposure to house dust mite or cat allergen were found, regardless of the definition of eczema used. The risk of eczema appeared to increase for the three lowest quintiles of house dust mite allergen exposure (odds ratio, OR 1 x 37 for third quintile compared with first), and then to fall for the two highest quintiles (OR 0 x 66 and 0 x 71) even after controlling for confounding factors. The lack of any clear exposure-disease relationship between allergens in early life and subsequent eczema argues against allergen exposure being a major factor causing eczema. If the lower levels of eczema at higher levels of house dust mite are confirmed, then interventions aimed at reducing house dust mite in early infancy could paradoxically increase the risk of subsequent eczema.