Do mite avoidance measures affect mite and cat airborne allergens?

Population growth and allergen accumulation of Dermatophagoides pteronyssinus cultured at 20 and 25 °C

The house dust mites, Dermatophagoides pteronyssinus and D. farinae are cultured commercially and in research laboratories and material is harvested from these cultures to make extracts that are used for diagnosis, immunotherapy and research. Temperature and other climatic conditions can influence population growth rates, dynamics of allergen production, and the associated endotoxin, enzyme and protein levels of the mite material harvested from these cultures. Here we determined how temperature affected these parameters. Dermatophagoides pteronyssinus was cultured at 20 and 25 °C at 75% relative humidity, and at 2-week intervals the concentrations of mites, Der p 1 and Der p 2 allergens, endotoxin, and selected enzymes were determined. Mite density increased exponentially but growth rate and final population density were greater at 25 °C compared to 20 °C. The combined allergen (Der p 1 + Der p 2) concentrations accumulated in the cultures at about the same rate at both temperatures. However, individual Der p 1 and Der p 2 accumulation rates varied independently at the two temperatures. Der p 1 accumulated faster at 20 °C whereas Der p 2 accumulated faster at 25 °C. The amount of Der p 1 in whole cultures was greater than the amount of Der p 2. The concentration of allergen for washed mites harvested from the cultures was much less than for the whole cultures. Our study demonstrated that temperature is an important factor in population growth and the dynamics of allergen production in cultured mites.

House dust mite control measures for asthma

EDITORIAL NOTE

This 2011 review predates current reporting standards and methodological expectations for Cochrane Reviews. It should not be used for clinical decision‐making.

BACKGROUND

The major allergen in house dust comes from mites. Chemical, physical and combined methods of reducing mite allergen levels are intended to reduce asthma symptoms in people who are sensitive to house dust mites.

OBJECTIVES

To assess the effects of reducing exposure to house dust mite antigens in the homes of people with mite-sensitive asthma.

SEARCH STRATEGY

PubMed and The Cochrane Library (last searches Nov 2007), reference lists.

SELECTION CRITERIA

Randomised trials of mite control measures vs placebo or no treatment in people with asthma known to be sensitive to house dust mites.

DATA COLLECTION AND ANALYSIS

Two authors applied the trial inclusion criteria and evaluated the data. Trial authors were contacted to clarify information.

MAIN RESULTS

Fifty-four trials (3002 patients) were included. Thirty-six trials assessed physical methods (26 mattress encasings), 10 chemical methods, and 8 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 standardised mean difference was 0.00 (95% confidence interval (CI) -0.10 to 0.10). There were no statistically significant differences either in number of patients improved (relative risk 1.01, 95% CI 0.80 to 1.27), asthma symptom scores (standardised mean difference -0.04, 95% CI -0.15 to 0.07), or in medication usage (standardised mean difference -0.06, 95% CI -0.18 to 0.07).

AUTHORS' CONCLUSIONS

Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended. It is doubtful whether further studies, similar to the ones in our review, are worthwhile. If other types of studies are considered, they should be methodologically rigorous and use other methods than those used so far, with careful monitoring of mite exposure and relevant clinical outcomes.

Treatment Options for the Management of Perennial Allergic Rhinitis, with a Focus on Intranasal Corticosteroids

Perennial allergic rhinitis (PAR) can have a significant impact on a patient's quality of life. While allergen avoidance is the first line of management for PAR, complete avoidance is difficult. Therapeutic options available for PAR include intranasal corticosteroids (INS), H1-antihistamines, decongestants and local chromones, as well as immunotherapy. For mild symptoms, INS and antihistamines are the standard of care, whereas for moderate-to-severe PAR, INS are the preferred therapy due to their proven efficacy. Patient quality of life and therapy preference play a role in maintaining adherence to treatment.

How is the indoor environment related to asthma?: literature review

AIMS

This paper reports a review conducted to identify the factors in the indoor environment that have an evidence-based link with the exacerbation or development of asthma and to identify measures that healthcare professionals can promote to reduce exposure to these risk factors in the home.

BACKGROUND

The indoor environment, particularly at home, has been recognized as a major source of exposure to allergens and toxic chemicals. Exposure to allergens and toxins is thought to exacerbate respiratory conditions, in particular, asthma.

METHODS

Searches were made of health and indoor environment databases, including Cochrane Library, National Health Services Centre for Reviews and Assessment Reports, British Medical Journal, CINAHL and Ovid library, MEDSCAPE/MEDLINE, EMBASE, INGENTA, Science Citation Index, Web of Science. Searches were also made of other Internet-based resources, including those of international and government bodies. The following keywords were used: allergens, allergen avoidance, asthma, asthma prevention, cat, damp, Der p 1, dog, environmental control, house dust mites, indoor air quality, indoor environment, meta analysis, mould, pets, remedial actions, respiratory illnesses and systematic reviews.

FINDINGS

There is evidence of a link between asthma and a small number of indoor environmental factors. There is currently only reasonable evidence for one causative factor for asthma in the indoor environment and that is house dust mite allergen. Although there are many studies of different remedial actions that can be taken in the home, often these give evidence of reduced risk of exposure but not clinical improvement in asthma. Although there is a lack of medical evidence for the reduction of known sensitizers such as mould, this is because of a dearth of research rather than evidence of no association.

CONCLUSIONS

There is some evidence of a link between the indoor environment and asthma. There are measures, which could be promoted by healthcare professionals to alleviate asthmatic symptoms.

House dust mite control measures for asthma

BACKGROUND

The major allergen in house dust comes from mites. Chemical, physical and combined methods of reducing mite allergen levels are intended to reduce asthma symptoms in people who are sensitive to house dust mites.

OBJECTIVES

To assess the effects of reducing exposure to house dust mite antigens in the homes of people with mite-sensitive asthma.

SEARCH STRATEGY

Cochrane Airways Group trials register, and PubMed and The Cochrane Library (last searches June 2004), reference lists.

SELECTION CRITERIA

Randomised trials of mite control measures vs placebo or no treatment in asthmatic people known to be sensitive to house dust mites.

DATA COLLECTION AND ANALYSIS

Two reviewers applied the trial inclusion criteria, assessed their quality and extracted the data independently. Study authors were contacted to clarify information.

MAIN RESULTS

Forty-nine trials (2733 patients) were included; the number of patients has more than doubled since the last version of this review. Thirty-one trials assessed physical methods, ten assessed 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 (1339 patients), the standardised mean difference was -0.02 (95% confidence interval (CI) -0.13 to 0.08). There were no statistically significant differences either in number of patients improved (relative risk 1.01, 95% CI 0.80 to 1.27), asthma symptom scores (standardised mean difference -0.01, 95% CI -0.10 to 0.13), or in medication usage (standardised mean difference -0.05, 95% CI -0.18 to 0.09).

REVIEWERS' CONCLUSIONS

Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended. It is doubtful whether further studies, similar to the ones in our meta-analysis, are worthwhile. If other types of studies are considered, they should be methodologically rigorous and use other methods than those used so far, with careful monitoring of mite exposure and relevant clinical outcomes.

Efficacy in allergen control and air permeability of different materials used for bed encasement

BACKGROUND

Different types of textile are used for the preparation of covers for bed encasement. The aim of the present study was to evaluate different fabrics employed for mattress covers regarding their efficacy in blocking Der p 1 and Fel d 1 as well as their air permeability.

METHODS

Eleven different commercially available fabrics manufactured for allergen avoidance have been tested and compared with regular cotton. Dust samples titered for Der p 1 and Fel d 1 were pulled through the different fabrics using a modified Fussnecker dust trap and collected by a filter located downstream. Airflow through the dust trap was controlled by a vacuum pump operating for 5 min and measured at the beginning (T0) and at the end (T1) of the test.

RESULTS

All the tightly woven and laminated materials were able to control mite allergen permeability allowing air passage but they significantly differed in Fel d 1 permeability. Laminated tissues and laminated tissue not tissued were effective in controlling both the allergens but they did not allow air permeability.

CONCLUSIONS

Detailed knowledge about the actual properties of the products for bed encasement needs to be considered in order to optimize allergen avoidance, disease control and sleep comfort.

The effects of housing interventions on child health

Housing hazards contribute to considerable morbidity and mortality among millions of children each year in the US, but few interventions are proven to control asthma and lead poisoning. Moreover, there is little evidence that many of the current recommendations to control residential hazards are safe and efficacious. The only interventions that have been found to work consistently are home visitation programs and home modification, such as installment of window guards and carpet removal. Altering the environment to protect the health of children requires pediatrician intervention. New models of cooperation between pediatricians and public health agencies must deal with residential hazards in an integrated manner and cannot be focused on one disease process or one method at a time. With research in more effective environmental interventions and pediatric-public-health partnerships, primary and secondary prevention of diseases from residential hazards may become a reality in the future.

Stringent environmental control in pregnancy and early life: the long-term effects on mite, cat and dog allergen

BACKGROUND

As part of a primary prevention of asthma study, we measured the effect of environmental control measures on Der p 1, Fel d 1 and Can f 1 over a 3.5-year period.

METHODS

High-risk infants (both parents atopic) without pets, were randomized to the Active group (n = 142, vinyl flooring in child's room, allergen-impermeable cot mattress, hot-washable toy, mite allergen-impermeable encasings to parental bed and to child's bed when older, high filtration vacuum cleaner, hot-washing of bedding) or the Control group (n = 136, no intervention), in early pregnancy. Dust samples from the parental mattress, living room floor, child's mattress and floor at baseline (pregnancy), birth and at 3 years were analysed for Der p 1, Fel d 1 and Can f 1.

RESULTS

A total of 278 families completed the baseline visit, 259 the birth visit and 239 the 3-year visit. In the Active group at 3 years, 58% remained compliant with all measures likely to reduce the child's exposure to allergen and 77% of parents still used encasings on their bed. Levels of Der p 1, Fel d 1 and Can f 1 were significantly lower in the Active group in the child's floor and the child's mattress at 3 years compared to the Control group (P < 0.001). For the parental mattress, the levels of Der p 1 and Fel d 1 were lower in the Active group (P < 0.001) and there was a strong trend towards a lower level for Can f 1. There was no difference in the levels of any of the allergens between the groups in the living room floor. Childrens' bedrooms with no detectable mite, cat or dog allergen were significantly more common in the Active than the Control group (25 vs. 2, P < 0.001).

CONCLUSIONS

Environmental control measures are effective in substantially reducing levels of Der p 1, Fel d 1 and Can f 1 in homes without pets in the long term and are acceptable to families. The effect of this environmental manipulation on the development of sensitization and allergic disease remains to be seen.

Four methods of sampling for dust mite allergen: differences in 'dust'

BACKGROUND

Measurement of exposure to the dust mite allergen Der p 1 is important in asthma research and is potentially useful in managing asthma. As no single measure can capture all characteristics of an exposure, it is important to recognize differences in the available methods of measuring exposure to Der p 1.

METHODS

Fourteen bedrooms and living rooms were sampled using four methods for 1 week. Airborne allergen was sampled by static Institute of Occupational Medicine samplers. Settling dust was collected on Petri dishes and an adhesive-membrane system (A-book). Vacuumed reservoir dust samples were collected from floors at the end of 1 week. Der p 1 was measured in all samples by enzyme-linked immunosorbent assay, except A-books, in which it was measured by Halogen immunoassay.

RESULTS

All four methods intercorrelated moderately (r range = 0.40-0.64, P = 0.04), except between allergen in reservoir dust (as microg/m2 and microg/g dust) and settling dust by Petri dishes (P = 0.2). Reservoir allergen, expressed as microg/m2, did not correlate with any measure, except reservoir allergen expressed as microg/g (r = 0.39, P = 0.04). No differences in these associations occurred between bedrooms and living rooms.

CONCLUSIONS

While the four methods examined correlated moderately, all have practical advantages and difficulties. No method can be considered as ideal for measuring individual exposure. For practicality, use of vacuum cleaner and Petri dish methods are recommended.

House dust mite allergen in US beds: results from the First National Survey of Lead and Allergens in Housing

BACKGROUND

Although exposure to house dust mite allergen is a major risk factor for allergic sensitization and asthma, nationwide estimates of dust mite allergen levels in US homes have not been reported.

OBJECTIVE

The purpose of this study was to estimate the prevalence of dust mite allergen in beds of US homes and to identify predictors of dust mite allergen concentration.

METHODS

Data were obtained from the first National Survey of Lead and Allergens in Housing, a cross-sectional survey of 831 permanently occupied noninstitutional housing units that permitted resident children. Dust mite allergen concentration (Der f 1 plus Der p 1) was determined from a dust sample collected from a bed. The percentages of homes with concentrations at or greater than detection, 2.0 microg/g bed dust, and 10.0 microg/g bed dust were estimated. Independent predictors of allergen concentration were assessed with multivariable linear regression.

RESULTS

The percentages of US homes with dust mite allergen concentrations at or greater than detection, 2.0 microg/g, and 10.0 microg/g were 84.2% (SE, 1.73), 46.2% (SE, 2.0), and 24.2% (SE, 2.1), respectively. Independent predictors of higher levels were older homes, non-West census regions, single-family homes, no resident children, lower household income, heating sources other than forced air, musty or mildew odor, and higher bedroom humidity.

CONCLUSION

Most US homes have detectable levels of dust mite allergen in a bed. Levels previously associated with allergic sensitization and asthma are common in US bedrooms. Predictors can be used to identify conditions under which homes are more likely to have increased dust mite allergen levels.

Effect of mattress and pillow encasings on children with asthma and house dust mite allergy

BACKGROUND

House dust mite (HDM) allergy is a frequent cause of allergic asthma in children. Reduction of exposure seems to be the most logical way to treat these patients.

OBJECTIVE

Our aim was to investigate whether mattress and pillow encasings resulted in an effective long-term control of HDM allergen levels, thereby reducing the need for asthma medication in children with asthma and HDM allergy.

METHODS

In a prospective, double-blind, placebo-controlled study 60 children (age range, 6-15 years) with asthma and HDM allergy were randomized to active (allergy control) or placebo mattress and pillow encasings. After a 2-week baseline period, follow-up was performed every 3 months for 1 year. During the entire study period, the dose of inhaled steroids was tapered off to the lowest effective dose according to well-defined criteria.

RESULTS

Fifty-two patients completed the trial, and 5 were excluded, leaving data from 47 children (26 in the active treatment group and 21 in the placebo group) for analysis. A significant perennial reduction in HDM allergen concentrations was seen only for the active treatment group. Also, a significant decrease in the dose of inhaled steroids (mean, 408 to 227 microg/d; P <.001) was found for the active treatment group only, with significant differences between groups after 9 and 12 months. After 1 year, the dose of inhaled steroids was reduced by at least 50% in significantly more children in the active treatment group than in the placebo group (73% vs 24%, P <.01).

CONCLUSION

Encasing of mattresses and pillows resulted in a significant long-term reduction in HDM allergen concentrations in mattresses and in the need for inhaled steroids in children with asthma and HDM allergy.

Effect of mattress encasings on atopic dermatitis outcome measures in a double-blind, placebo-controlled study: the Dutch mite avoidance study

BACKGROUND

House dust mite (HDM) allergen might induce and maintain atopic dermatitis (AD). Reduction of allergen load by applying encasings might improve the clinical symptoms of AD.

OBJECTIVE

We sought to investigate, in a randomized, double-blind, placebo-controlled study, whether reducing HDM allergen levels by using mattress, duvet, and pillow encasings for 12 months will result in improvement in AD symptoms.

METHODS

Patients with AD (8-50 years old and allergic to HDM), having a Leicester sign score (a dermatitis score) of at least 1% extent and a severity score of 6 points or greater, were randomly allocated to an active (n = 45) or a placebo allergen-avoidance group (n = 41). Avoidance measures consisted of applying HDM-impermeable encasings for mattresses, pillows, and duvets for the active treatment group and cotton encasings for the placebo group. Effect on allergen concentrations (Der p 1 and Der p 1 plus Der f 1), Leicester sign score extent and severity, visual analogue scale scores for itching and sleeplessness, intradermal test results, atopy patch test results, total serum IgE levels, anti-Der p 1-specific IgE levels, and total blood eosinophil counts were studied.

RESULTS

The active encasings reduced the Der p 1 allergen concentration in the mattress after 12 months with a factor 2.1 (P =.007) and the Der p 1 plus Der f 1 allergen concentration with a factor of 2.5 (P =.005); no significant change in allergen concentrations in mattresses was seen in the placebo group. Although the decrease in allergen load was significant, no differences in treatment-induced changes were seen between the placebo and active groups.

CONCLUSIONS

Use of HDM-impermeable encasings resulted in a significant decrease in Der p 1 and Der p 1 plus Der f 1 allergen concentrations. However, this reduction in allergen load did not result in significant changes in clinical parameters between the groups. Reduction of allergens in other environments (work, school, and outdoors) might be equally important in improving symptoms of AD.

Prevention of sensitization to house dust mite by allergen avoidance in school age children: a randomized controlled study

BACKGROUND

Sensitization to dust mites predisposes to asthma and allergic rhinitis, and prevention of this sensitization might reduce the rising prevalence of these disorders.

OBJECTIVE

To test the effectiveness of dust mite avoidance measures on the development of sensitization to dust mites in children.

METHODS

As part of a multicentre study (Study of Prevention of Allergy in Children of Europe), 242 children, aged 5-7 years, in three European countries (United Kingdom, Greece and Lithuania), were randomized to prophylactic group (n = 127) and control group (n = 115). At randomization these children were required to have a family history of atopy and positive skin test to an aeroallergen but not to house dust mite. Children in the prophylactic group were provided with dust mite impermeable mattress covers and advice on environmental measures to reduce exposure to dust-mite allergen. Control group children were given non-specific advice. After 12 months a standardized questionnaire was completed and skin prick tests were performed.

RESULTS

Ten children in the prophylactic group and 19 in the control group were lost to follow-up. Three of 117 (2.56%) children in the prophylactic group and nine of 96 (9.38%) in the control group developed sensitization to dust mites. Logistic regression analysis confirmed an independent effect of prophylactic measures (adjusted odds ratio (OR): 0.14, 95% confidence interval (CI): 0.03-0.79, P = 0.03). Fifteen children need to be treated to prevent sensitization in one child.

CONCLUSION

Dust mite sensitization can be reduced in school age children with simple mite avoidance measures.

Evaluation of Petri dish sampling for assessment of cat allergen in airborne dust

BACKGROUND

Dust reservoir sampling is the most commonly used method for assessment of indirect allergen exposure. Because assessment of personal exposure using person-carried pumps is time-consuming and expensive we evaluated the Petri dish sampling method for measurement of airborne cat allergen in classrooms.

METHODS

Petri dish sampling was evaluated in three study parts. Part I: by comparison between Petri dish sampling and personal air sampling in 44 classrooms with many (> or = 20%) and few (< or = 10%) cat owners and by additional Petri dish sampling in 40 pet-free homes. Part II: by sampling with duplicate Petri dishes in 28 classrooms. Part III: by sampling in three classrooms at four sampling heights during different sampling times. All samples were analyzed for cat allergen (Fel d 1) content with a monoclonal antibody two-site ELISA (enzyme linked immunosorbent assay), using signal amplification when necessary.

RESULTS

There was a significant correlation between Petri dish sampling and personal air sampling (r = 0.66; P < 0.0001). Levels were five-fold higher in classes with many cat owners than in classes with few cat owners, regardless of method. A corresponding difference was found in the homes. Duplicate sample values were in fair agreement (Bland-Altman test) and were correlated (r = 0.77; P < 0.0001). Cumulative levels collected weekly in one Petri dish were lower than using five daily Petri dishes, regardless of sampling height.

CONCLUSIONS

Petri dish sampling can be useful as an alternative method to personal air sampling of airborne allergens.

Effectiveness of occlusive bedding in the treatment of atopic dermatitis--a placebo-controlled trial of 12 months' duration

BACKGROUND

Several studies on avoidance of house-dust-mite (HDM) and cat allergens have been carried out, most of them in asthmatic patients and only a few in patients with atopic dermatitis (AD). No study so far has focused on which subgroup of AD patients benefits from avoidance measures.

METHODS

Forty adult patients with AD completed the 12-month avoidance study. They were divided into an active treatment (n = 22) and a placebo (n = 18) group. Active treatment comprised use of polyurethane-coated cotton encasings for bedding, and placebo use of cotton covers. Patients came for regular checkups during the 12-month period, when eczema severity was assessed and blood samples were analyzed for total IgE, HDM- and cat-specific IgE and soluble CD30 (sCD30) in serum. Dust samples were collected from mattresses before treatment and after 3, 6, and 12 months, and analyzed for content of HDM and cat allergen.

RESULTS

Eczema severity decreased significantly in both groups (P < 0.001), with a more pronounced decrease in patients with active covers. The HDM exposure decreased significantly in the active treatment group (P < 0.001), and the levels of HDM-specific IgE were reduced (P<0.05). Exposure to cat allergens was unchanged in the active treatment group but decreased, albeit not significantly (P=0.19), in the placebo group. sCD30 levels were significantly reduced in both groups (P<0.001). Patients not sensitized to HDM allergens benefited from the bedcovers as much as sensitized patients.

CONCLUSIONS

Occlusive bedding significantly reduced HDM exposure in bed (P<0.001) and eczema severity, and sCD30 levels decreased significantly (P<0.001). Patients not sensitized to HDM and not exposed to HDM allergens benefited equally from use of the bedcovers, a result which could be due to a reduction of other important allergens, superantigens, or irritants in bed. We therefore recommend the use of bedcovers as part of treatment for AD.