The house dust mite is the most important environmental allergen implicated in the aetiology of childhood asthma in the UK. Dust mite barrier bedding is relatively inexpensive, convenient to use, and of proven effectiveness in reducing mattress house dust mite load, but no studies have evaluated its clinical effectiveness in the control of childhood asthma when dispensed in primary care. We therefore aimed to evaluate the effectiveness of house dust mite barrier bedding in children with asthma treated in primary care.
Pragmatic, randomised, double-blind, placebo controlled trial conducted in eight family practices in England. Forty-seven children aged 5 to 14 years with confirmed house dust mite sensitive asthma were randomised to receive six months treatment with either house dust mite barrier or placebo bedding. Peak expiratory flow was the main outcome measure of interest; secondary outcome measures included asthma symptom scores and asthma medication usage.
No difference was noted in mean monthly peak expiratory flow, asthma symptom score, medication usage or asthma consultations, between children who received active bedding and those who received placebo bedding.
Treating house dust mite sensitive asthmatic children in primary care with house dust mite barrier bedding for six months failed to improve peak expiratory flow. Results strongly suggest that the intervention made no impact upon other clinical features of asthma.
Twenty-one children with mite-sensitive asthma took part in a crossover randomised controlled trial of mite-free bedding. Each child was issued with a new sleeping bag and pillow for a month, and twice-daily peak flow readings were compared with those obtained during a month in the child's ordinary bedding. Seventeen of the children had higher mean peak flow readings during the period in the mite-free bedding (p < 0.01). The overall improvement was only modest, however, and some mites had appeared in most of the bedding by the end of the trial. New bedding may be helpful to patients with mite-sensitive asthma, but methods are needed to prevent colonisation by mites.
House dust mite allergen exposure is a postulated risk factor for allergic sensitization, asthma development, and asthma morbidity; however, practical and effective methods to mitigate these allergens from low-income, urban home environments remain elusive. The purpose of this study was to assess the feasibility and effectiveness of physical interventions to mitigate house dust mite allergens in this setting. Homes with high levels of house dust mite allergen (Der f 1 + Der p 1 > or = 10 microg/g dust by enzyme-linked immunosorbent assay) in the bed, bedroom carpet, and/or upholstered furniture were enrolled in the study. Carpets and upholstered furniture were subjected to a single treatment of either dry steam cleaning plus vacuuming (carpet only) or intensive vacuuming alone. Bed interventions consisted of complete encasement of the mattress, box spring, and pillows plus either weekly professional or in-home laundering of nonencased bedding. Dust samples were collected at baseline and again at 3 days (carpet and upholstery only) and 2, 4, and 8 weeks posttreatment. We compared pretreatment mean allergen concentrations and loads to posttreatment values and performed between-group analyses after adjusting for differences in the pretreatment means. Both dry steam cleaning plus vacuuming and vacuuming alone resulted in a significant reduction in carpet house dust mite allergen concentration and load (p < 0.05). Levels approached pretreatment values by 4 weeks posttreatment in the intensive vacuuming group, whereas steam cleaning plus vacuuming effected a decrease that persisted for up to 8 weeks. Significant decreases in bed house dust mite allergen concentration and load were obtained in response to encasement and either professional or in-home laundering (p < 0.001). Between-group analysis revealed significantly less postintervention house dust mite allergen load in professionally laundered compared to home-laundered beds (p < 0.05). Intensive vacuuming and dry steam cleaning both caused a significant reduction in allergen concentration and load in upholstered furniture samples (p < 0.005). Based on these data, we conclude that physical interventions offer practical, effective means of reducing house dust mite allergen levels in low-income, urban home environments.
Sensitization to the house dust mite (Dermataphagoides pteronyssinus) (HDM) is the most common risk factor associated with the development of asthma in adults and children. The effectiveness of HDM control measures in the treatment of asthma is not yet proven. The strategies for control for avoidance depend on our understanding of the biology of the HDM. The evidence suggests a favorable effect of transferring allergic asthmatic children to naturally low dust mite environments, such as at altitude or in hospital, but little to suggest that this can be replicated in general practice by simple practical measures such as mattress covers. However, a recent multi-allergen reduction approach has suggested benefits may be achievable. HDM densities tend to be high in warm, humid conditions in the home, which may be modified by external factors, such as ventilation. However, ventilation control to reduce indoor humidity has had inconsistent effects on dust mite levels and asthma. The challenge is to further refine the interventions in large placebo-controlled trials such that clinical outcomes may be more easily demonstrated.
house dust mite; asthma; allergy; control
Mite counts and tests for mite antigen were performed on samples of dust taken from the bedding of 53 children with mite-sensitive asthma. The samples from damp houses and the beds or enuretic children had markedly more mites and mite-antigen than those from dry houses. although the predominant species was usually Dermatophagoides pteronyssinus, some of the beds in the damp houses were heavily infested with another pyroglyphid mite Euroglyphus maynei, so that this was the species found in the greatest numbers. D pteronyssinus antigen was found to be correlated broadly with the total mite count, but more antigen was present for a given number of mites in the mattresses than in the blankets. The children were randomly allocated into two groups, one of which carried out rigorous anti-mite measures. The amounts of dust and mite antigen were reduced, though not the numbers of mites. Peak flow readings were monitored in the two groups for eight weeks and a final assessment made by a paediatrician who was unaware of the allocation of each patient in the trial. No significant differences emerged in the progress of the two groups, both tending to improve. Measures designed to remove mites from bedding do not greatly benefit the majority of children with mite-sensitive asthma.
Exposure to indoor air pollutants such as tobacco smoke and dust mites may exacerbate childhood asthma. Environmental interventions to reduce exposures to these pollutants can help prevent exacerbations of the disease. Among the most important interventions is the elimination of environmental tobacco smoke from the environments of children with asthma. However, the effectiveness of reducing asthmatic children's exposure to environmental tobacco smoke on the severity of their symptoms has not yet been systematically evaluated. Dust mite reduction is another helpful environmental intervention. This can be achieved by enclosing the child's mattresses, blankets, and pillows in zippered polyurethane-coated casings. Primary prevention of asthma is not as well understood. It is anticipated that efforts to reduce smoking during pregnancy could reduce the incidence of asthma in children. European studies have suggested that reducing exposure to food and house dust mite antigens during lactation and for the first 12 months of life diminishes the development of allergic disorders in infants with high total IgE in the cord blood and a family history of atopy. Many children with asthma and their families are not receiving adequate counseling about environmental interventions from health care providers or other sources.
A trial of the effects of measures designed to reduce exposure to house-dust mites was performed on 14 children with mite-sensitive asthma. These measures reduced mite infestation of the beds and were associated with clinical improvement of asthmatic symptoms. Immunological studies revealed a tendency for levels of total serum IgE to fall during the course of the trial, but no such changes were apparent in the levels of anti-mite specific serum IgE. Possible reasons for this discrepancy are discussed.
The conclusion of the study is that the use of a plastic mattress cover and the other inexpensive and harmless avoidance measures described should be advised for all asthmatic children with evidence of mite-sensitivity before resort to drug prophylaxis or hyposensitization procedures.
House dust mite sensitized asthmatics are advised to practice allergen avoidance. Charcoal pillows are used in Korea with unsubstantiated claims regarding their efficacy in alleviating asthma symptoms. We tested the effects of activated charcoal on breeding of house dust mites in culture. Twenty live adult house dust mites (Dermatophagoides pteronyssinus) were inoculated, 10 replicates, on culture media containing 0%, 1%, 3%, 5%, 10%, and 20% activated charcoal and incubated at 25℃ and a relative humidity of 75%. After four weeks, the mean numbers of live house dust mites were 286, 176, 46, 16, 7, and 0 for the 0%, 1%, 3%, 5%, 10%, and 20% charcoal-containing culture media, respectively. Thus, activated charcoal suppresses breeding of house dust mites and offers a new promising method for house dust mite control.
Dermatophagoides Pteronyssinus; House Dust Mite; Activated Charcoal; Survival; Allergy
The efficacy of bed covers that are impermeable to house dust mites has been disputed.
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.
Primary care in a south-eastern region of the Netherlands.
Asthma patients aged between 16 and 60 years with a house dust mite allergy requiring ICS were randomised to intevention 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.
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.
House dust mite impermeable bed covers combined with self-management do not lead to reduced use of ICS compared with self-management alone.
allergy; asthma; corticosteriods; house dust mites; inhalation; self management
Pillows are known to contain significant levels of indoor allergens and endotoxin, that are of importance to house dust mite sensitized asthmatics. Buckwheat pillows are commonly used in Korea. We studied the levels of the house dust mite allergen, Der f 1, and endotoxin on new synthetic and buckwheat pillows and their accumulation over three months. Endotoxin levels were significantly higher on new buckwheat pillows compared to synthetic pillows; geometric mean levels (95% CI) were 60,950 EU/g (30,270-122,700) and 4,887 EU/g (2,570-9,311) respectively (p<0.001). No Der f 1 was detected on the new pillows. After three months Der f 1 levels were similar on buckwheat and synthetic pillows, geometric mean levels (95% CI) were 1.16 µg/g (0.02-8.13) and 1.08 µg/g (0.19-1.68) respectively. These results indicate that buckwheat pillows are a source of very high endotoxin levels that may be of relevance to asthma severity of atopic asthmatics.
Pillows; Buckwheat; Endotoxins; House Dust Mite; Dermatophagoides pteronyssinus; Dermatophagoides farinae; Asthma; Atopy
We examined the impact of a combination of home environmental interventions and nurse case management services on total settled dust loadings and on allergen concentrations in the homes of asthmatic children.
Using a randomized longitudinal controlled trial study design, we randomly assigned homes of asthmatic children in Milwaukee to either a control (n=64) or an intervention (n=57) group. Control group homes received a visual assessment, education, bed/pillow dust mite encasings, and treatment of lead-based paint hazards. The intervention group received these same services plus nurse case management that included tailored, individual asthma action plans, provision of minor home repairs, home cleaning using special vacuuming and wet washing, and integrated pest management. Dust vacuum samples were collected from measured surface areas of floors in the TV room, kitchen, and child's bedroom at baseline and at three-, six-, and 12-month follow-up visits. Dust loading (mass per surface area) is a means of measuring total dust and the total amount of allergen present.
For the intervention group, geometric mean dust loadings declined significantly from baseline (39 milligrams per square foot [mg/ft2]) to post-intervention (11 mg/ft2) (p<0.001). Baseline dust loading, treatment group, visit, and season were significant predictors of follow-up dust loadings. Mean post-intervention dust loadings were 72% higher in the control group. The total amount of allergen in settled house dust declined significantly following the intervention because total dust loading declined; the concentration of allergens in settled dust did not change significantly.
The combination of nurse case management and home environmental interventions promotes collaboration between health and housing professionals and is effective in reducing exposures to allergens in settled dust.
Background: The relationship between cough receptor sensitivity and eosinophilic inflammation of the airway in patients with asthma remains unclear.
Methods: Eighteen patients with asthma sensitised to house dust mite (HDM) were enrolled in a randomised parallel group study. Patients with asthma whose main symptom was cough were not enrolled in the study. Half the patients were randomly assigned to inhale saline and the other half to inhale HDM allergen. Cough receptor sensitivity to capsaicin, airway responsiveness to histamine, and sputum eosinophils analysed with hypertonic saline inhalation were investigated before and 24 hours after saline or HDM allergen bronchoprovocation.
Results: Patients inhaling saline showed no significant changes in sputum eosinophils (from 7.87% (95% confidence interval (CI) 5.08 to 12.19) to 8.60% (95% CI 3.03 to 14.18); p=0.97), airway responsiveness to histamine (from 726.68 µg/ml (95% CI 251.90 to 2096.36) to 773.01 µg/ml (95% CI 251.36 to 2377.23); p=0.96), or capsaicin sensitivity (from 7.23 µM (95% CI 2.45 to 21.31) to 7.24 µM (95% CI 2.46 to 21.31); p=0.96). Early asthmatic response was induced in all patients, and late asthmatic response was observed in six of nine patients inhaling HDM allergen. Although there were significant increases in sputum eosinophils (from 9.83% (95% CI 6.78 to 14.27) to 21.00% (95% CI 13.85 to 28.15); p<0.01) and airway responsiveness to histamine (from 784.16 µg/ml (95% CI 318.24 to 1932.24) to 377.81 µg/ml (95% CI 118.43 to 1205.24); p<0.05) 24 hours after HDM allergen inhalation compared with baseline levels, capsaicin sensitivity did not change significantly (from 5.75 µM (95% CI 1.91 to 17.30) to 6.20 µM (95% CI 2.21 to 17.38); p=0.77).
Conclusions: These findings suggest that cough receptor sensitivity to capsaicin is not associated with eosinophilic inflammation of the airway in patients with allergic asthma whose main symptoms are wheezing and dyspnoea but not cough.
Objective To determine whether patients with asthma who are sensitive to mites benefit from measures designed to reduce their exposure to house dust mite antigen in the home.
Design Meta-analysis of randomised trials that investigated the effects on asthma patients of chemical or physical measures to control mites, or both, in comparison with an untreated control group. All trials in any language were eligible for inclusion.
Subjects Patients with bronchial asthma as diagnosed by a doctor and sensitisation to mites as determined by skin prick testing, bronchial provocation testing, or serum assays for specific IgE antibodies.
Main outcome measures Number of patients whose allergic symptoms improved, improvement in asthma symptoms, improvement in peak expiratory flow rate. Outcomes measured on different scales were combined using the standardised effect size method (the difference in effect was divided by the standard deviation of the measurements).
Results 23 studies were included in the meta-analysis; 6 studies used chemical methods to reduce exposure to mites, 13 used physical methods, and 4 used a combination. Altogether, 41/113 patients exposed to treatment interventions improved compared with 38/117 in the control groups (odds ratio 1.20, 95% confidence interval 0.66 to 2.18). The standardised mean difference for improvement in asthma symptoms was −0.06 (95% confidence interval −0.54 to 0.41). For peak flow rate measured in the morning the standardised mean difference was −0.03 (−0.25 to 0.19). As measured in the original units this difference between the treatment and the control group corresponds to −3 l/min (95% confidence interval −25 l/min to 19 l/min). The results were similar in the subgroups of trials that reported successful reduction in exposure to mites or had long follow up times.
Conclusion Current chemical and physical methods aimed at reducing exposure to allergens from house dust mites seem to be ineffective and cannot be recommended as prophylactic treatment for asthma patients sensitive to mites.
Key messagesCurrent chemical and physical methods aimed at reducing exposure to allergens from house dust mites seem to be ineffective; these methods cannot be recommended as prophylactic treatment for asthma patients who are sensitive to mitesIt is unlikely that a worthwhile effect has been overlooked in this meta-analysis since the confidence interval for the peak expiratory flow rate was quite narrowFuture studies should be much larger and more rigorous than those in this meta-analysis and should evaluate other methods of mite control than those used to date
We evaluated the efficacy of health education in reducing indoor arthropod allergens in Seoul. The mite control measures comprised the use of mite-proof mattress and pillow coverings, regular washing of potentially infested materials, maintenance of a low humidity, removal of carpets, and frequent vacuum cleaning. Cockroach control measures included trapping, application of insecticides, and protecting food. Of 201 homes enrolled in October 1999, 63 volunteers were included in a 2-year follow-up survey between April 2000 and January 2002. Before intervention, the density of mites/g of dust varied greatly; 27.1/g in children's bedding, 20/g in adult bedding, 7.2/g on the floors of children's bedrooms, 6.8/g in sofas, 5.9/g on the floors of adult's bedrooms, 3.9/g on living room floors, 3.7/g in carpets, and 1.9 mites/g on kitchen floors. The predominant mite species and house percentages infested were; Dermatophagoides farinae 93%, D. pteronyssinus 9%, and Tyrophagus putrescentiae 8%. Comparing 1999 and 2001 infestations, before and after 25 mo of education, mite abundance was reduced by 98%, from 23.7 to 0.57 mites/g of dust. In 1999, cockroaches were detected in 62% homes: 36% Blattella germanica and 35% Periplaneta spp., including 9% double infestations of B. germanica and P. americana. Following intervention, cockroach infestation rates decreased to 22% of houses in 2000 and 23% in 2001. We conclude that continuous and repetitive health education resulted in the effective control of domestic arthropods.
Blattella germanica; Dermatophagoides farinae; Periplaneta americana; Periplaneta fuliginosa; Periplaneta japonica; Tyrophagus putrescentiae; aeroallergens; allergy prevention; cockroaches; house dust mites
The aetiological importance of the house-dust mite, Dermatophagoides sp., was examined in 133 asthmatic children referred to hospital. Evidence of sensitization to this allergen from positive skin tests and the presence of circulating specific IgE was found in the majority of these children and sensitization often began in the preschool years. In vitro studies of specific IgE levels were found to bear a close relation to nasal provocation tests and probably have an important place in the identification of offending allergens in the paediatric patient.
Ecological studies of the house-dust mite revealed its common occurrence in domestic environments, especially in the bed and bedroom. The mites were not found in hospital beds and only low levels of infestation were found in perambulators and cots and in residential schools for `delicate' children. The findings stress the major importance of this allergen in the causation of childhood asthma.
fractional exhaled NO concentrations (FENO) and
blood/tissue eosinophilia are frequently reported in allergic children with mild asthma and are thought to reflect the intensity of the inflammation characterising the disease. The aim of this study was to
investigate possible differences in FENO levels or in the intensity of the blood eosinophilia in allergic and non-allergic asthmatic children.
with stable, mild, intermittent asthma with a positive bronchial
challenge to methacholine were consecutively enrolled in the study; 56 were skin prick test and RAST negative (non-sensitised) while 56 were
sensitised to house dust mites (23 only to house dust mites
(monosensitised) and 33 were sensitised to mites and at least another
class of allergens (pollens, pet danders, or moulds)). Nineteen sex and
age matched healthy children formed a control group.
with non-allergic patients, allergic children had a significantly
higher rate of blood eosinophilia (p=0.0001) with no differences
between mono- and polysensitised individuals. Forced expiratory volume
in 1 second (FEV1), forced vital capacity (FVC), forced
expiratory flow at 25-75% of vital capacity
(FEF25-75%), and the degree of bronchial reactivity to
methacholine were similar in non-atopic and atopic children, with no
differences between mono- and polysensitised individuals.
FENO levels measured by chemiluminescence analyser were
higher in asthmatic children (15.9(14.3) ppb) than in the control
group (7.6 (1.6) ppb, p=0.04) and higher in allergic patients (23.9 (2.1) ppb) than in non-allergic patients (7.9 (0.8) ppb, p=0.0001),
but there were no differences between mono- and polysensitised
individuals (p>0.1). Significant correlations between blood
eosinophilia and FENO levels were seen only in allergic
(r=0.35, p<0.01) and in polysensitised
individuals (r=0.45, p<0.05).
children with mild asthma, a similar degree of functional disease
severity may be associated with a higher inflammatory component in
allergic than in non-allergic subjects.
The clinical features of perennial asthmatic children with a skin or bronchial reaction to the house dust mite (Dermatophagoides pteronyssinus) were compared with those of asthmatic children without mite sensitivity. Mite sensitive asthma was characterised by an early age of onset of symptoms, these being predominantly nocturnal. A history of wheezing precipitated by dust exposure, during vacuuming, bedmaking, or dusting was present in 52% of cases. Asthmatic children with mite sensitivity were more likely to have been born at the time of the year when mite counts were highest. This was consistent with the idea that allergy may be associated with a period of susceptibility to sensitisation in early infancy.
Aims: To determine the frequency of sensitisation to mites among rhinitic laboratory animal workers and to clarify whether sensitisation could be occupational.
Methods: Skin prick tests (SPT) were performed in 40 subjects who were working with laboratory animals in Kuopio University research units and who had been referred to Kuopio University Hospital for work related rhinitis. The SPT panel consisted of three storage mites, two house dust mites, 11 other common environmental airborne allergens, latex, and 2–4 individually relevant laboratory animals. To determine signs of mites in animal facilities, guanine was determined in 22 dust samples taken from feedstuffs or bedding material used for laboratory animals and from rooms where these materials were stored and handled.
Results: Positive SPT results were found in 35 out of 40 workers: in 14 for storage mites, four for house dust mites, 25 for other common aeroallergens, as well as positive reactions to laboratory animals in 19 individuals. The guanine test was positive, indicating the presence of mite derived material in 21 out of 22 dust samples.
Conclusions: This study suggests that subjects who are occupationally exposed to laboratory animals are also exposed to mite derived allergens. Sensitisation to mites is common and may be work related.
Hypersensitivity to house dust mite (HDM; Dermatophagoides sp.) allergens is one of the most common allergic responses, affecting up to 85% of asthmatics. Sensitization to indoor allergens is the strongest independent risk factor associated with asthma. Additionally, >50% of children and adolescents with asthma are sensitized to HDM. Although allergen-specific CD4+ Th2 cells orchestrate the HDM allergic response through induction of IgE directed toward mite allergens, activation of innate immunity also plays a critical role in HDM-induced allergic inflammation. This review highlights the HDM components that lead to activation of the innate immune response. Activation may due to HDM proteases. Proteases may be recognized by protease-activation receptors (PARs), Toll-like receptors (TLRs), or C-type lectin receptors (CTRs), or act as a molecular mimic for PAMP activation signaling pathways. Understanding the role of mite allergen-induced innate immunity will facilitate the development of therapeutic strategies that exploit innate immunity receptors and associated signaling pathways for the treatment of allergic asthma.
House dust mites; innate immunity; toll-like receptors; C-type lectin receptors; dendritic cells
Identifying toddlers at increased risk of developing persistent wheeze provides an opportunity for risk-reducing interventions. House dust mite (HDM) allergen sensitization might identify this group of high-risk children.
We examined whether a positive skin prick test (SPT) to at least 1 of the 3 HDMs in wheezing toddlers, would serve as a predictor for persistent wheeze at age 8 to 14 years old.
A cohort of 78 children, who had wheezing episodes, and underwent SPT to 3 HDMs between the ages of 2 to 5 years old, were enrolled. SPT results were obtained from the National University Hospital database. Four to 9 years later, the children, currently between 8 to 14 years old, were re-assessed for persistence of asthma symptoms and other atopic disorders via a telephone interview. A validated questionnaire on current wheezing and asthma, developed by the International Study of Asthma and Allergies in Childhood, was used. Fisher's exact test was used to evaluate the association between persistence of asthma and a positive SPT.
Of the 78 children who participated in the study, 42 (53.8%) had a positive SPT and 36 (46.2%) had a negative SPT. Of these, 18 (42.9%) of SPT positive and 7 (19.4%) of SPT negative children had persistence of asthma symptoms. There is a significant association between a positive SPT during the preschool years, and persistence of asthma (p = 0.0314 [<0.05]).
HDM sensitization at ages 2 to 5 years old in wheezing children predicts persistence of asthma after 4 to 9 years. This in turn may have benefits for management of asthma in this high-risk group.
Dust mite; Allergy; Asthma; Wheezing; Skin tests; Child
Twenty one adult patients with asthma, with positive skin test responses to the European house dust mite, Dermatophagoides pteronyssinus, were randomly allocated to a control group or to a group applying house dust mite avoidance measures. These included an initial application of liquid nitrogen to mattresses and bedroom carpets to kill the live house dust mite population. Histamine airway responsiveness, symptom scores, peak expiratory flow rates (PEF), and house dust mite numbers were determined during the two week pretrial and eight week trial periods. Nine patients in each group completed the study. By the end of the study there was a significant reduction in live mites in the "avoidance" group but not in the control group. The avoidance group showed a significant improvement in symptom scores measured on a linear analogue scale, in the number of hours each day spent wheezing (mean reduced from 8.6 to 4.5 hours), and in PEF (l/min) both in the morning (from 364 to 388) and in the evening (from 368 to 392). These changes were not found in the control group. The provocative concentration (PC) of histamine causing a 20% fall in FEV1 (PC20FEV1) had increased significantly in the avoidance group at eight weeks (from 0.58 to 2.3 mg/ml), whereas no change was seen in the control group (from 0.93 to 1.21 mg/ml). These results show that house dust mite avoidance, combined with initial killing of the mite by liquid nitrogen, diminishes airway responsiveness and improves asthma symptom control over an eight week period in adult asthmatic patients with house dust mite allergy.
OBJECTIVE--To investigate the effects of the home environment on the risk of severe asthma during adolescence. DESIGN--A questionnaire based case-control study drawn from a cross sectional survey of allergic diseases among secondary school pupils in Sheffield in 1991. SUBJECTS--763 children whose parents had reported that over the previous 12 months they had suffered either 12 or more wheezing attacks or a speech limiting attack of wheeze. A further 763 children were frequency matched for age and school class to act as controls. Analysis was restricted to 486 affected children and 475 others born between 1975 and 1980 who had lived at their present address for more than three years. RESULTS--Independent associations with severe wheeze were seen for non-feather bedding, especially foam pillows (odds ratio 2.78; 95% confidence interval 1.89 to 4.17), and the ownership of furry pets now (1.51; 1.04 to 2.20) and at birth (1.70; 1.20 to 2.40). These estimates were derived from subjects whose parents denied making changes in the bedroom or avoiding having a pet because of allergy. Parental smoking, use of gas for cooking, age of mattress, and mould growth in the child's bedroom were not significantly associated with wheezing. CONCLUSIONS--Either our study questionnaire failed to detect the avoidance or removal of feather bedding by allergic families or there is some undetermined hazard related to foam pillows. Synthetic bedding and furry pets were both widespread in this population and may represent remediable causes of childhood asthma.
Background: The use of anti-allergic mattress covers in patients with asthma can result in a large reduction in the level of house dust mite allergen in dust samples. Apart from a reduction in histamine induced bronchial hyperresponsiveness, there are few data on the effect of mattress covers on clinical efficacy and quality of life in patients with moderate to severe asthma.
Methods: Thirty patients with asthma and house dust mite allergy were studied in a randomised, double blind, placebo controlled study. Before and after using anti-allergic covers for 1 year, dust was collected from the mattresses to determine concentrations of Dermatophagoides pteronyssinus (Der p 1), and bronchial hyperresponsiveness and quality of life were measured. The patients scored their symptoms (lungs and nose), morning and evening peak flow values, and rescue medication for 14 days before and after the intervention period.
Results: There was a significant reduction in the concentration of Der p 1 in the dust collected from the mattresses in the actively treated group after 1 year compared with before treatment; no change was found in the placebo group. In both the actively treated and placebo groups there was no significant improvement in PC20 histamine. Quality of life improved similarly in both groups. The symptom score of the lower airways did not significantly change in either group. A significant decrease in nasal symptom score was seen in the actively treated group compared with before treatment, but there was no significant difference between the groups. No changes in morning and evening peak flow values, peak flow variability, nor in the use of rescue medication were found in either group.
Conclusion: The use of anti-allergic mattress covers results in significant reductions in Der p 1 concentrations in carpet-free bedrooms. However, in patients with moderate to severe asthma, airways hyperresponsiveness and clinical parameters are not affected by this effective allergen avoidance.
Background: The effect of exposure to allergens not causing sensitisation in atopic asthmatic subjects has not previously been studied. A study was undertaken to assess the degree of asthma severity (measured by spirometry, airway reactivity and exhaled nitric oxide) in atopic asthmatic patients not sensitised to the domestic allergen to which they were exposed.
Methods: Dust samples were collected from the living room carpet and mattress in the homes of 248 subjects and dust mite, cat and dog allergen concentrations were measured. Spirometry, non-specific bronchial reactivity (BR), and exhaled nitric oxide (eNO) were ascertained. Patients' sensitisation status was assessed by skin prick testing.
Results: Adult atopic asthmatics not sensitised to mite but exposed to high levels of mite allergen had significantly more severe BR than subjects not exposed to high levels of mite (PD20, geometric mean (GM) 0.21 mg (95% CI 0.09 to 0.47) v 0.86 mg (95% CI 0.44 to 1.67), mean ratio difference 4.1 (95% CI 1.5 to 11.4), p = 0.008). Subjects not sensitised but exposed to high levels of dog allergen also had significantly more severe BR than subjects not exposed (PD20 GM 0.16 v 0.52 mg, mean ratio difference 3.3 (95% CI 1.2 to 9.2), p = 0.01). The differences in BR between these groups were still significant after adjusting for confounding factors. This effect of greater airway reactivity was not seen in subjects exposed but not sensitised to cat allergens.
Conclusion: Atopic asthmatic subjects who are exposed to high levels of dust mite or dog allergens but not sensitised to these allergens have evidence of increased airway reactivity.
The variability of repeated house dust mite (HDM) allergen determinations at the same site within 3-24 months was evaluated on previously collected samples. Between two and four repeated measurements of Der p 1, a major allergen of Dermatophagoides pteronyssinus and Der f 1, a major allergen of D. farinae, on 46 carpets and 31 mattresses were analyzed. In 90% of carpets and mattresses, HDM allergen concentrations were clinically relevant (at least one measurement >0.1 microg Der p 1 + Der f 1/g dust). The coefficients of variation (CVs) for allergen concentrations in repeated samples over time (55.3-82.0% for the two allergens in beds and carpets) were clearly greater than the CVs for multiple samples collected at the same time (4.0-32.6%). Determination of allergen mass per square meter of surface instead of concentration per gram of dust resulted in an even greater CV (72.3-86.7%). The 95% range of expected values was about 10-fold above and below the result of a single determination. We conclude that single determinations of HDM allergen in dust give very limited information about long-term exposure of an individual to the allergen. Repeated measurements are recommended. Studies of factors that affect HDM allergen exposure must be planned with appropriate sample sizes.