House dust mite allergen avoidance and self-management in allergic patients with asthma: randomised controlled trial

BACKGROUND: The efficacy of bed covers that are impermeable to house dust mites has been disputed. AIM: The aim of the present study was to investigate whether the combination of 'house dust mite impermeable' covers and a self-management plan, based on peak flow values and symptoms, leads to reduced use of inhaled corticosteroids (ICS) than self-management alone. DESIGN OF STUDY: Prospective, randomised, double blind, placebo-controlled trial. SETTING: Primary care in a south-eastern region of the Netherlands. METHOD: Asthma patients aged between 16 and 60 years with a house dust mite allergy requiring ICS were randomised to intervention and placebo groups. They were trained to use a self-management plan based on peak flow and symptoms. After a 3-month training period, the intervention commenced using house dust mite impermeable and placebo bed covers. The follow-up period was 2 years. Primary outcome was the use of ICS; secondary outcomes were peak expiratory flow parameters, asthma control, and symptoms. RESULTS: One hundred and twenty-six patients started the intervention with house dust mite impermeable or placebo bed covers. After 1 and 2 years, significant differences in allergen exposure were found between the intervention and control groups (P<0.001). No significant difference between the intervention and control groups was found in the dose of ICS (P = 0.08), morning peak flow (P = 0.52), peak flow variability (P = 0.36), dyspnoea (P = 0.46), wheezing (P = 0.77), or coughing (P = 0.41). There was no difference in asthma control between the intervention and control groups. CONCLUSION: House dust mite impermeable bed covers combined with self-management do not lead to reduced use of ICS compared with self-management alone.     

Birth month and sensitization to house dust mites in asthmatic children

Background: Early exposure to high quantities of allergen has an important role in the incidence of atopic sensitization. In fact, subjects sensitized to house dust mites (HDMs) have a significantly higher proportion of births in the season when HDMs are most abundant. Objective: The aim of this study was to investigate whether birth month patterns differ for asthmatic patients sensitized only to HDMs and for those sensitized to HDMs and other allergen(s). Methods: Among 2225 patients with asthma, aged 10–16 years, 1642 sensitized to HDMs were identified by skin prick testing. This group was composed of patients sensitized only to HDMs (n = 715) and patients sensitized to HDMs and other allergen(s) (n = 927). The birth month distributions of the group of HDM-sensitive asthmatics or its subgroups were compared with that of a reference population (total live births in the same years as the studied subjects). The risk ratio of a given birth month in relation to all the other months was calculated as an odds ratio (OR) with the corresponding 95% confidence interval (CI). Results: A significant difference in birth month distribution was observed for HDM-sensitive asthmatics (χ² = 23.6, P = 0.015), with higher rates of birth in August (OR: 1.23, 95% CI: 1.04–1.46) and September (1.24, 1.04–1.46). When the two subgroups were analyzed separately, significantly more births were noted in August (1.34, 1.06–1.71) and September (1.34, 1.05–1.70) for those sensitized only to HDMs, whereas no such birth month preference was observed for those sensitized to HDMs and other allergen(s). Conclusions: The HDM-positive asthmatics showed a greater proportion of births in August and September, which correspond to high HDM exposure. However, this birth month pattern was evident in asthmatic-sensitive only to HDMs, but was not observed in those sensitive to HDMs and other allergen(s).     

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.     

Seasonal differences in airway hyperresponsiveness in asthmatic patients: relationship with allergen exposure and sensitization to house dust mites

Background The degree of airway hyperresponsiveness in allergic asthmatic patients may be influenced by changes in environmental exposure to inhalant allergens. Objective This study investigates the relationship between seasonal changes in exposure to house dust mite (HDM) allergens and non-specific airway hyperresponsiveness in asthmatic patients with multiple sensitizations to inhaled allergens. Methods In 43 asthmatic patients sensitized to several inhalant allergens, lung function (FEV₁), airway hyperresponsiveness (PC₂₀ histamine), serum total IgE, house dust mite (HDM) specific IgE and number of peripheral blood eosinophils were measured during autumn 1990 (September-November) and spring 1991 (March—May). During each season. floor dust samples were collected twice from living- and bedrooms and the concentration of the HDM allergens Der p 1 and Der p 2 determined. Results More severe airway hyperresponsiveness (lower PC₂₀ histamine) during autumn was only found in patients sensitized to HDM(n= 32; autumn: 2.05mg/mL, spring: 4.51mg/mL (geometric means), P <0.0 1), whereas in patients not sensitized to HDM (n= 11) similar values were observed in both seasons (3.44 and 4.52 mg/mL. respectively, P= 0.56). More severe airway hyperresponsiveness of HDM sensitized patients in autumn was significantly associated with higher Der p 1 concentrations in floor dust. Aside from airway hyperresponsiveness, seasonal changes in serum total IgE and number of peripheral blood eosinophils were seen in patients sensitized to HDM, Conclusions In allergic asthmatic patients, airway hyperresponsiveness may increase during autumn, depending on sensitization to HDM and an increase of exposure to HDM allergen.     

A randomized trial of dehumidification in the control of house dust mite

BACKGROUND: House dust mites (HDM) are sensitive to humidity. Few studies have adequately examined the potential of dehumidification in reducing HDM numbers. OBJECTIVE: The study examined the effect of portable domestic dehumidifiers, and a behavioural programme to reduce humidity, on HDM counts and HDM allergen levels. METHODS: A randomized controlled trial was undertaken. A total of 76 homes were allocated to three groups that received a portable domestic dehumidifier, a behavioural programme, or no intervention. Humidity, temperature, HDM counts (trap and vacuum samples), HDM allergen, and other details of the home environment were measured on four occasions over a period of 1 year. Interventions and measurements were concerned predominantly with one bedroom. RESULTS: There was a reduction in relative humidity in the dehumidifier group, but not the behavioural group. A decline in HDM trap counts was observed for all three groups. Change scores did not indicate that the dehumidifier group had a greater decline than the other groups. A secondary analysis examining presence or absence of HDM showed a shift from households having HDM at baseline to households not having HDM in the final round for some trap measures. Change score analysis indicated that this shift was greater in the dehumidifier group compared with other groups. The dehumidifier group did not show a greater decline in HDM allergen than that seen in the other two groups. CONCLUSION: Neither the dehumidifier nor the behavioural intervention had a major effect on HDM counts or allergen levels. However, the study did have a number of limitations relating to size, timing of intervention, and running of the dehumidifiers. The secondary data analysis may indicate some effect of dehumidification, but clearly this effect was small. There is a need for more information on the effects of reducing ambient humidity on the distribution of HDM within their habitats.     

It's time to rethink mite allergen avoidance

The role of allergen exposure in the etiology of allergic sensitization and asthma is complex. Advice on strategies to avoid domestic allergens remains contentious because trials of interventions aimed to prevent asthma or reduce symptoms have often failed to demonstrate benefits. Asthma management guidelines differ widely in their recommendations, while Web-based information often claims benefits associated with products. In this rostrum we argue that although many factors have a role in both the etiology and the exacerbation of asthma, allergen exposure probably remains an important contributor to the manifestations of the disease. Currently, there is no evidence-based framework for effective domestic allergen avoidance interventions to reduce chronic aeroallergen exposure. The development of an effective approach to allergen avoidance requires a better understanding of (a) the physical nature of chronic aeroallergen exposure and methods for measuring and reducing this, (b) the interaction between allergen exposure and innate immune modulators at different disease stages, and (c) markers enabling the identification of individuals who would benefit from this. The strategic risk of overemphasizing other novel mechanisms and approaches to asthma management is that we will prematurely abandon and fail to improve an existing approach that could have a significant impact on the development, progression, and symptoms of the disease.     

哮喘患儿家庭内尘螨过敏原分布特征及其临床意义

目的了解北京地区尘螨过敏性哮喘患儿家庭环境内尘螨过敏原含量分布特征,初步探讨尘螨过敏原暴露水平的临床意义。方法选取54例尘螨过敏性哮喘患儿,其中男性37例,女性17例;年龄3～16岁,平均年龄8岁2个月。采集患儿家庭中床垫、枕头、卧室地板、客厅地板及沙发的灰尘,采用酶联免疫吸附分析（ELISA）测定以上灰尘样本中户尘螨1组过敏原（Der p1）和粉尘螨1组过敏原（Der f1）的含量;应用荧光ELISA测定患儿血清尘螨特异性IgE浓度;评估患儿哮喘临床控制情况,应用化学发光法测定患儿呼出气一氧化氮浓度（FeNO）。结果采集灰尘样本255份,以中位数（最小值～最大值）表示尘螨过敏原含量,床垫、枕头和沙发灰尘样本中Derf1和Derp1的含量显著高于卧室地板和客厅地板灰尘样本中尘螨过敏原含量。Derf1平均含量为0.13μg/g,显著高于Derp1平均含量0.02μg/g（P〈0.05）。Derp1和Derf1联合暴露的最高含量平均为2.18（0.07～54.59）μg/g。Der p1和Der f1联合最高暴露含量≥10.00μg/g、2.00～10.00μg/g、0.05～2.00μg/g的例数分别为4例（7.4%）、24例（44.4%）、26例（48.1%）。其中未控制组患儿家庭内尘螨过敏原最高暴露水平为27.41（0.23～54.59）μg/g,均显著高于部分控制组和控制组哮喘患儿尘螨过敏原最高暴露水平1.66（0.07～26.27）μg/g、2.90（0.37～33.75）μg/g（P〈0.05）。不同sIgE浓度分级组间尘螨过敏原最高暴露水平的差异、不同FeNO浓度范围组间尘螨过敏原最高暴露水平差异均无统计学意义。结论北京地区尘螨过敏性哮喘患儿家庭尘螨以Der f1为主,床垫、枕头及沙发灰尘样本是Der p1和Der f1的主要来源;哮喘未控制者的尘螨过敏原最高暴露水平明显增高。     

Exposure to house dust endotoxin and allergic sensitization in adults

BACKGROUND: It has been suggested that exposure to elevated levels of endotoxin decreases the risk of allergic sensitization. OBJECTIVE: To examine the associations between current exposure to bacterial endotoxin in house dust and allergic sensitization in adults. METHODS: In 1995-1996, we conducted a nested case-control study following a cross-sectional study performed within the European Community Respiratory Health Survey (ECRHS). Data of 350 adults aged 25-50 years was analysed. Allergic sensitization was assessed by measurement of specific immunoglobulin E (IgE) against several inhalant allergens. Living room floor dust samples were taken. The endotoxin content was quantified using a chromogenic kinetic Limulus amoebocyte lysate test. RESULTS: Multiple logistic regression analysis showed a negative association between exposure to house dust endotoxin and severe allergic sensitization. Odds ratios (95% CI) adjusted for place of residence, gender, age, and 'caseness' were 0.80 (0.64-1.00) for sensitization to >/=1 allergen and 0.72 (0.56, 0.92) for sensitization to >/=2 allergens using 3.5 kU/l as a cut-off value for sensitization. With regard to single allergens, the protective effect of endotoxin was strongest for pollen sensitization [aOR (95% CI) = 0.74 (0.58, 0.93)]. CONCLUSION: Our results indicate that current exposure to higher levels of house dust endotoxin might be associated with a decreased odds of allergic sensitization in adults.     

House dust mite control measures for asthma: systematic review

The major allergen in house dust comes from mites. We performed a systematic review of the randomized trials that had assessed the effects of reducing exposure to house dust mite antigens in the homes of people with mite-sensitive asthma, and had compared active interventions with placebo or no treatment. Fifty-four trials (3002 patients) were included. Thirty-six trials assessed physical methods (26 mattress covers), 10 chemical methods and eight a combination of chemical and physical methods. Despite the fact that many trials were of poor quality and would be expected to exaggerate the reported effect, we did not find an effect of the interventions. For the most frequently reported outcome, peak flow in the morning (1565 patients), the standardized mean difference was 0.00 (95% confidence interval (CI) −0.10 to 0.10). There were no statistically significant differences in number of patients improved (relative risk 1.01, 95% CI 0.80–1.27), asthma symptom scores (standardized mean difference −0.04, 95% CI −0.15 to 0.07) or in medication usage (standardized mean difference −0.06, 95% CI −0.18 to 0.07). Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended.     

Prevention of new sensitizations in asthmatic children monosensitized to house dust mite by specific immunotherapy. A six-year follow-up study.

BACKGROUND: Specific immunotherapy (SIT) is a recognized way of treating IgE-mediated respiratory diseases. The clinical outcome is usually better in allergic children than in adults. OBJECTIVE: To increase our knowledge of the ability of SIT to prevent the onset of new sensitizations in monosensitized subjects, so far poorly documented. METHODS: 134 children (age range 5-8 years), who had intermittent asthma with or without rhinitis, with single sensitization to mite allergen (skin prick test and serum-specific IgE), were enrolled. SIT was proposed to all the children's parents, but was accepted by only 75 of them (SIT Group). The remaining 63 children were treated with medication only, and were considered the Control Group. Injective SIT with mite mix was administered to the SIT Group during the first three years and all patients were followed for a total of 6 years. All patients were checked for allergic sensitization(s) by skin prick test and serum-specific IgE every year until the end of the follow-up period. RESULTS: Both groups were comparable in terms of age, sex and disease characteristics. 123 children completed the follow-up study. At the end of the study, 52 out of 69 children (75.4%) in the SIT Group showed no new sensitization, compared to 18 out of 54 children (33.3%) in the Control Group (P < 0.0002). Parietaria, Gramineae and Olea were the most common allergens responsible for the new sensitization(s). CONCLUSIONS: According to our data, SIT may prevent the onset of new sensitizations in children with respiratory symptoms monosensitized to house dust mite (HDM).     

New mattresses: how fast do they become a significant source of exposure to house dust mite allergens?

Background Sensitization and exposure to mile allergens is a major risk factor for asthma. Little is known about the rate of build-up of allergens in the mite microhabitats. Objectives To investigate the rate of increase in mite allergen levels in new mattresses. Methods Der p 1 was measured in the dust samples collected from six identical new single mattresses over a period of 2 years. Results Der p 1 increased significantly at 4 months as compared with baseline level (P < 0.01), but no difference was found between the concentrations at 4. 8, 12 and 24 months. There was a significant correlation between Der p 1 concentration in mattresses at 4.8, 12 and 24 months and Der p 1 levels in the bedroom carpet at the beginning of the study. Conclusions New mattresses can become a significant source of exposure to mite allergens after a short period of time (< 4 months). There is little justification for advising mite sensitive patients to replace their mattresses as a part of avoidance regime.     

Determinants of house dust mite allergen in homes in Wellington, New Zealand

Objectives To measure levels of the major Dermatophagoides pteronyssinus allergen (Der p 1) in homes in Wellington, New Zealand, and to examine factors which affect these levels. Methods As part of a study of risk factors for asthma among 474 8–10-year-old children, standard procedures were used to collect reservoir dust and to measure Der p 1 levels on the living room floor and child's bedroom floor and bedding. Der p 1 levels were analysed both as geometric mean μg/g of fine dust and as μg/m². Questionnaires collected information about factors which might influence these levels, and an average relative humidity in the bed and on the bedroom floor was also measured. Results Similar geometric mean levels of Der p 1 were found at each floor site – 25.5μg/g (95% CI: 22.8–28.5) in the living room and 26.4 μg/g (95% CI: 23.7–29.3) on the child's bedroom floor. The geometric mean level of Der p 1 in the child's bed was 46.6 μg/g (95% CI: 42.3–51.3). After controlling for possible confounders, geometric mean living room and bedroom floor Der p 1 levels were significantly higher in households with older carpet than households with no carpets or newer carpets, and higher in the autumn. Households with three or more children had higher levels of Der p 1 than households with fewer children. Bedding levels were significantly higher in beds with kapok or inner sprung mattresses, or wool underlays and at relative humidities above the mean (51%). Conclusion The very high levels of house dust mite allergen (Der p 1) found in Wellington are likely to be due to a variety of life-style and climatic factors. However, the type and age of floor covering appears to be the single most important factor.     

Effect of improved home ventilation on asthma control and house dust mite allergen levels

Background:  The warm, humid environment in modern homes favours the dust mite population, but the effect of improved home ventilation on asthma control has not been established. We tested the hypothesis that a domestic mechanical heat recovery ventilation system (MHRV), in addition to allergen avoidance measures, can improve asthma control by attenuating re-colonization rates.
Methods:  We conducted a randomized double-blind placebo-controlled parallel group trial of the installation of MHRV activated in half the homes of 120 adults with asthma, allergic to Dermatophagoides pteronyssinus . All homes had carpets steam cleaned and new bedding and mattress covers at baseline. The primary outcome was morning peak expiratory flow (PEF) at 12 months.
Results:  At 12 months, the primary end-point; change in mean morning PEF as compared with baseline, did not differ between the MHRV group and the control group (mean difference 13.5 l/min, 95% CI: −2.6 to 29.8, P  = 0.10). However, a secondary end-point; evening mean PEF, was significantly improved in the MHRV group (mean difference 24.5 l/min, 95% CI: 8.9–40.1, P  = 0.002). Indoor relative humidity was reduced in MHRV homes, but there was no difference between the groups in Der p 1 levels, compared with baseline.
Conclusions:  The addition of MHRV to house dust mite eradication strategies did not achieve a reduction in mite allergen levels, but did improve evening PEF.