SEARCH

SEARCH BY CITATION

Keywords:

  • atopic eczema/dermatitis syndrome;
  • allergic asthma;
  • allergic rhinitis;
  • encasings;
  • house dust mite;
  • random regression;
  • short form 36

Abstract

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

Background:  Environmental control has been put forward as an integral part of the management of house dust mite (HDM) allergy in sensitized patients. To validate this statement allergic disorders involved in HDM allergy – allergic asthma, rhinitis and atopic eczema/dermatitis syndrome (AEDS) – should be taken together and studied in terms of the efficacy of environmental control. Because a generic quality of life questionnaire exceeds the border of disease, this may be used as major outcome parameter.

Research objective:  To study the effects of bedding encasings in HDM allergic patients with asthma, rhinitis and AEDS.

Material and methods:  A total of 224 adult HDM allergic patients with rhinitis and/or asthma and/or dermatitis were randomly allocated impermeable or nonimpermeable encasings for mattress, pillow and duvet. Short form 36 (SF-36) was filled in at baseline and after 12 months.

Results:  Lower physical (P = 0.01) and emotional (P < 0.001) sumscores were seen in females. Also, the presence of asthma resulted in lower physical sumscore (P = 0.01). However, no effect was seen of encasings on either sumscore.

Conclusion:  Bedding encasings do not improve quality of life in a mixed population of subjects with combinations with rhinitis, asthma and atopic dermatitis and sensitized to HDMs.

Environmental control has been put forward as an integral part of management of house dust mite (HDM) allergy in sensitized patients (1, 2). Analysing the various methods in a randomized-controlled clinical trial (RCT) has been proven difficult. So far, only application of chemical substances and physical barriers has been appropriately tested in a RCT. The results of studies to the efficacy of encasings on both symptoms of asthma and atopic eczema/dermatitis syndrome (AEDS) have been conflicting; in rhinitis only one randomized trial has been performed with negative results (3–10). Comparison of effects in different diseases will be hampered by differences in clinical presentation and outcome measures. However, when studying the effects of an intervention in patients with atopic disease, one may easily encounter subjects with multiple atopic disorders (11). To test the hypothesis that the use of encasings is effective in rhinitis, asthma and AEDS, ideally a common outcome measure should be used, capturing all the different aspects of these diseases.

The growing interest in quality of life research in the last decades has provided us with new tools for the evaluation of disease. The availability of generic quality of life questionnaires enables us to address the question whether encasings are effective in patients with HDM allergy, irrespective of their affected organ whereas disease-specific questionnaires only inform us about one selected organ. The use of a generic quality of life questionnaire, a common outcome for different diseases, may be particularly appropriate for these patients with more than one atopic disorder. In particular, the generic short form 36 (SF-36) serves our purpose as this instrument has been used in the evaluation of allergic rhinitis, asthma and atopic dermatitis (12–17). We studied the effect of encasings in HDM allergic patients with one or more atopic disorder. Our goal was to evaluate the effects of encasings on allergic complaints of asthma, rhinitis and AEDS by means of SF-36.

Patients

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

Patients took part in a double-blind, placebo-controlled, multicentre trial to study the effect of bedding encasings on complaints of allergic rhinitis and/or asthma and/or AEDS. Participating centres were the Allergology departments of the University Hospitals of Groningen and Rotterdam and the Dermatology department of the University Hospital Utrecht. The study was approved by the Medical Ethics Committees of all three University Hospitals and all patients gave written informed consent. Participants were adult HDM allergic patients suffering from atopic rhinitis, atopic asthma and/or AEDS in varying degrees of severity. House dust mite allergy was assessed by skin test and/or radioallergosorbent test (RAST) (18, 19). In- and exclusion criteria are described in Table 1. Patients were diagnosed as having rhinitis, asthma or AEDS according to preset criteria described elsewhere (20). Follow-up consisted of baseline visits and visits after 12 months. Before each visit nasal medication, both antihistaminics and nasal sprays, was stopped and replaced by acrivastine; acrivastine was stopped 3 days before baseline and follow-up visits. Class 3 and 4 topical corticosteroids for the skin were replaced by class 1 and 2 corticosteroids. Asthma medication was continued but all relevant medication was stopped before lung function tests. The mean PC20 showed room for improvement at baseline measurements (Z. Tempels, personal communication). Exacerbations were treated by the general practitioner or the specialist of the patient. After these visits a trained student visited the patient at home to obtain dust samples of the mattress, bedroom floor and living room floor. All measurements took place in autumn (September until November 1997, 1998 and 1999) since this is the HDM season in the Netherlands; also we avoided interference by pollen because pollen disappear at the beginning of September.

Table 1.  Inclusion and exclusion criteria
Inclusion criteriaExclusion criteria
  1. RAST, radioallergosorbent technique.

Age 8–50 yearsPets at home and positive skin test (index ≥0.7) (18, 19) and/or RAST ≥2 for the pet
Not pregnant or breast-feedingDaily use of inhalation steroids ≥1600 mcg/day (adults) or ≥800 mcg/day (children)
No encasings or willing to remove them for the period of the studyDaily use of oral steroids
Allergic rhinitis and/or asthma and/or atopic eczema/dermatitis syndromeDaily use of cyclosporine
RAST class ≥2 and/or intracutaneous skin test index ≥0.7 for house dust miteRegular use of antibiotics for upper or lower airway infection
≥200 ng Der p1 of F1 in dust sample of mattressRegular use of oral steroids for exacerbation of asthma

End-points of the study

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

Generic quality of life was measured by means of the SF-36. We used the translation of Aaronson of the MOS SF-36, originally developed by Ware and coworkers (21–25). The SF-36 consists of 36 questions divided over eight subscales, covering both physical and mental health. Physical health subscales are physical functioning, role physical functioning, bodily pain and general health; mental health subscales are mental health, role mental functioning, social functioning and vitality. Questions are stated in both yes/no form and multiple choice. Sumscore was calculated for each subscale and transformed to a percentage of the total possible score. After transforming subscale scores average score was taken for physical subscales (physical sumscore) and for emotional subscales (emotional sumscore). The reliability in two general population samples as reported by Aaronson using Cronbach's α varied from 0.76 to 0.92 while the item discriminant validities varied from 0.09 to 0.64.

The SF-36 was administered to the patient before tests were performed. Trained personnel instructed the patient according to the guidelines, defined by the designers of the questionnaires. All patients filled in their questionnaires in a private room without the presence of other persons.

Blinding and randomization procedures

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

If a patient was considered eligible, he or she was taken into the randomization procedure: initials, date of birth and the measures of all pillows, duvets and mattress(es) were faxed to the Julius Centre for Patient-oriented Research. Each patient was assigned a research number. Research number and measures were sent by the Julius Centre to the manufacturer of the encasings, HAL, Haarlem, the Netherlands. A carton box, containing all encasings, was sent to the research centre, with the research number written on the outside of the box. Patients were instructed to take the box home and apply the encasings after baseline visits in absence of the research staff. We did not check if the encasings were in use since that would have compromised the blinding.

Statistical analysis

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

Categorical variables were analysed with chi-square test. anova was used to compare continuous variables. Data were analysed using Statistical Analysis Systems (SAS) statistical programme. The levels and the dispersion of the data were represented by mean values and standard deviations, respectively. To analyse longitudinal data Random Regression Modelling (RRM) for continuous data was applied. The RRM is a highly flexible and proper approach for repeated measurements. The RRM enables to model change across time and at both group and individual level. The qualities of RRM above and beyond to multivariate anova for repeated measurements is that RRM is not restricted to modelling time as fixed effect; on the contrary, in RRM both the number of measurements across time and the moments of measurement may vary. Time-constant and time-varying variables can be entered in RRM. The structural form of the within subject covariance matrix of manova for repeated measurements is assumed to meet the criteria of ‘compound symmetry’, that is to say that the variances and covariances are assumed to be constant across time. The RRM, however, is utmost flexible in that variances and covariances across time may assume other kinds of error structure. In this study, it is assumed to be unstructured (fully parameterized). In addition, RRM can handle missing data if the missing data can be assumed to be missing at random (26). This implies that patients who were missing at a given measurement moment, were not excluded from analysis.

The RRM estimates the trend (of any kind) across time for every patient on the basis of individual data, augmented by time trend being for all patients together and the effects of all covariables in the model, including centre as a confounding variable.

The analysis strategy was as follows:

Model 1 comprised fixed terms such as linear time trend and treatment condition without any interaction; only the intercept was considered to vary randomly. Model 2 was identical to model 1 but different in that in this model the quadratic time trend was added. In model 3, linear time trend was added as random term to model 1. Model 4 equals model 2 including linear time trend as random term. Model 5 is different from model 4 only in that in the first mentioned model quadratic time trend was added as random term. Models 6–10 were similar to models 1–5 consecutively; however, the interaction of linear time trend and treatment was entered. Models 11–15 corresponded to models 6–10, only now the interaction of quadratic time trend and treatment was included. All 15 models were applied on both the sumscore of all physical subscales of the SF-36 (FF) and on the sumscore of all emotional subscales of the SF-36 (EF). Since the distributions of the sumscore of both FF and EF were skewed to the right, log-value was calculated of FF and EF after transformation being log(101 – FF) or log(101 – EF), respectively. The models were fitted by maximizing the likelihood function for the data. The likelihood function (L) measures the likelihood of the parameters given the data and is defined by the density function of the observations. Akaike's information criterion (AIC) makes allowance for the number of parameters fitted; AIC enables to make comparisons between models fitting the same fixed effects (27). In addition, Schwarz's information criterion (SIC) takes into account the number of fixed effects, the number of covariance parameters and the number of observations (28). Models with larger values of AIC and SIC indicate better fits. To statistically test for fixed effects of the models the difference of −2 restricted log-likelihood ratios for the respective models is estimated along with the corresponding degrees of freedom. Testing for random effect runs as follows: the P-values of the models with degrees of freedom belonging to the respective models were averaged.

General results

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

At baseline 224 patients entered the study. All baseline parameters were equally distributed between both groups (Table 2). Loss to follow-up is described in Fig. 1; no significant differences were found between the impermeable and nonimpermeable encasing group. Mean baseline scores on SF-36 physical and emotional subscales were not significantly different in both groups, neither were both sumscores; in comparison with the general Dutch population, the scores on the subscales were significantly lower on almost every subscale (Table 3). Most patients suffered from rhinitis (85), rhinitis and asthma (62) or rhinitis, asthma and AEDS (31); 20 patients had rhinitis and AEDS, five had asthma and AEDS, 13 suffered from only asthma and eight patients had only AEDS.

Table 2.  Baseline parameters
 Impermeable encasing group (N = 113)Nonimpermeable encasing group (N = 111)
  1. * Results are expressed as mean (SD).

  2. † Results are expressed as number of patients (%).

  3. ICT, intracutaneous skin test; a ratio (allergen wheal diameter divided by histamine wheal diameter) ≥0.7 is positive; VAS, visual analogue scale 0–100 mm, 0 representing no complaints, 100 very severe complaints; AEDS, atopic eczema/dermatitis syndrome.

Age*31.5 (8.1)33.4 (8.2)
Male†41 (18.3)39 (17.4)
Smokers†23 (10.3)17 (7.6)
Rhinitis†100 (44.6)98 (43.8)
Asthma†53 (23.7)58 (25.9)
AEDS†31 (13.8)33 (14.7)
VAS rhinitis*48.4 (29.7)50.3 (29.6)
ICT*1.2 (0.35)1.3 (0.37)
Blood eosinophils (106/l)*293 (220)286 (195)
image

Figure 1. Patients enrolled, randomized and withdrawn from trial.

Download figure to PowerPoint

Table 3.  General score on SF-36 subscales
 National study (N = 1742)This study (N = 224)P-valueAR (n = 85)AR + AA (n = 62)AR + AA + AEDS (n = 31)
  1. Results are expressed as mean (SD).

  2. * Only GH was significantly different between AR and AR + AA + AEDS (P = 0.004).

  3. PF, physical functioning; RP, role physical functioning; BP, bodily pain; GH, general health; MH, mental health; RE, role emotional functioning; SF, social functioning; VT, vitality; SF-36, short form 36.

PF93.1 (11.8)85.2 (15.8)<0.0186.9 (16.6)84.0 (14.3)81.6 (15.2)
RP86.4 (27.6)78.0 (33.2)<0.0181.5 (31.4)74.6 (37.2)75.8 (33.8)
BP80.9 (19.4)80.5 (20.3)>0.0579.9 (21)82.0 (20.0)76.6 (20)
GH78.2 (17.3)63.8 (21.3)<0.0167.2 (22)*61.5 (20.1)54.2 (19.6)*
VT70.7 (16.4)64.8 (19.3)<0.0165.9 (20.6)64.9 (16.8)60.5 (22.6)
SF87.8 (19.1)84.9 (20.1)<0.0186.0 (20.6)85.9 (21.3)84.3 (14.4)
RE85.4 (30.0)86.6 (29.1)>0.0586.3 (29.2)83.9 (31.8)88.2 (28)
MH78.7 (15.2)79.1 (14.7)>0.0579.2 (14.7)79.4 (15.5)80.4 (15)

Random regression modelling

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

We applied all 15 models described above on the physical sumscore (FF) and the emotional sumscore (EF). For the physical sumscore model 1 was by far the best fitting model (data not shown); model 3 was the best model for emotional sumscore (data not shown). When considering the results of both models in detail, a few aspects strike the eye immediately (Table 4). Treatment – the use of encasings on mattress, pillow and duvet – has no effect in this analysis. Less surprising was the finding that females indicated to have a lower physical and emotional sumscore (scores were log-transformed after subtraction of the sumscore as described in the statistical paragraph), which is in line with earlier results of this study (20). The negative effect of asthma – presence of asthma resulted in lower physical sumscores – is also in line with earlier findings (20). The linear time trend is significant in physical sumscore but the effect (estimate −0.01) is negligible.

Table 4.  Results of best fitting model for physical and emotional sumscore of SF-36
 Estimate*SEt-valueP-value95% CI
  1. * Estimate: unstandardized regression coefficient adjusted for centre.

  2. CI, confidence interval; SF-36, short form 36; AEDS, atopic eczema/dermatitis syndrome; SE, standard error of the estimate.

Physical sumscore
 Intercept0.990.156.79<0.0010.70–1.27
 Linear time trend−0.010.00−3.130.002−0.01 to 0.00
 Treatment0.030.050.650.51−0.07 to 0.13
 Sex0.140.052.530.010.03–0.24
 Age0.000.000.990.320.00–0.01
 AEDS0.050.060.880.38−0.06 to 0.17
 Asthma0.130.052.560.010.03–0.23
 Rhinitis−0.030.08−0.320.75−0.19 to 0.14
Emotional sumscore
 Intercept1.280.1111.8<0.0011.07–1.50
 Linear time trend0.000.00−1.670.10−0.01 to 0.00
 Treatment0.040.040.950.34−0.04 to 0.11
 Sex0.100.042.550.010.02–0.18
 Age0.000.000.390.700.00–0.01
 AEDS0.040.040.850.39−0.04 to 0.12
 Asthma−0.030.04−0.860.39−0.10 to 0.04
 Rhinitis−0.080.06−1.290.20−0.20 to 0.04

Discussion

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

The goal of this study was to evaluate the effect of encasings in HDM allergic patients by means of a general quality of life questionnaire, the SF-36. In an earlier study encasings had no effect on clinical outcome measures-like visual analogue scale or daily symptom score in spite of a significant reduction on allergen exposure (10). In this study, we could not demonstrate any effect of encasings on quality of life scores assessed by SF-36; we did find a negative impact of asthma and sex. This was also in line with the result of an earlier study (20). Before accepting these results, potential limitations of this study have to be addressed. First, lack of effect could be due to inefficacy of the encasings. However, as reported elsewhere the results of the dust samples at baseline and after 12 months clearly showed a significant threefold reduction in favour of the impermeable encasing group (6, 10). Secondly, allergens from other sources may modulate the effects of intervention in multisensitized subjects. Interference by other relevant allergens has been avoided by evaluation of patients outside the pollen season and by not allowing pets in case of sensitization to pets. Allergy to moulds or cockroach was not investigated since this is not an important problem in the Netherlands (30). In contrast, neither dust mite exposure from other sources in the house, nor exposure to other allergens outside the house was controlled in this study. Perhaps the use of encasings as a mono-intervention does not sufficiently reduce allergen exposure to ameliorate symptoms. It is also possible that the HDM is not responsible for eliciting symptoms although all patients had a positive skin test. The relation between atopic eczema and HDM allergy is still a matter of controversy although Tupker could induce skin responses in patients with AEDS after bronchial provocation with HDM (31). Bronchial provocation with HDM can induce a response in asthma patients, but since we only performed challenge tests with methacholine and adenosine, it is possible that in some of our asthma patients HDM does not elicite a bronchial response. However, we assume that we included subjects with asthma because of HDM exposure, knowing that the degree of allergic sensitization and the degree of bronchial hyperreactivity may predict the bronchial response to allergens (29). The diagnosis of rhinitis could only be obtained if a suggestive history was followed by a positive nasal challenge test with HDM allergen; so, in this patient group we are certain that allergen exposure was responsible for nasal complaints.

Finally, one could speculate that the instrument used, the SF-36, might have been a less adequate choice in terms of responsiveness to change and that a disease-specific questionnaire might have been a better option. Although generic instruments are less-sensitive in detecting treatment effects, our results are backed up by separate analyses using medical outcome measures in children and adults with AEDS and in rhinitis (6, 10, 20, 32).

As discussed earlier, the choice of outcome measure was linked to and warranted by the aims of this study. We chose to evaluate the intervention in this mixed population instead of focusing on a distinct group of subjects with rhinitis, asthma or atopic dermatitis for the following reasons. Not only would the latter approach lower the number of eligible patients, but more importantly, we considered these patients with combined atopic disorders as representative of the allergic subjects seen and treated in daily practice. In addition, according to position papers environmental control has been advocated to subjects allergic to HDMs in general.

The commonly accepted statement that environmental control is an integral part of the management in patients sensitized to HDMs has been based on early observations that children with asthma and allergy to HDMs recover at HDM-free high altitudes (33). Moreover, it appeared that a long-term stay in hospital induced a decrease in bronchial hyperreactivity in asthmatic subjects allergic to HDMs (34). It may be possible, however, that the beneficial effects of an allergen-free environment cannot be obtained by HDM reducing measures in our daily environment (34). Our study corresponds with both a recent meta-analysis of 29 trials in 939 asthmatic patients, showing that neither physical methods (15 trials), chemical methods (nine trials) nor a combination of methods (five trials) resulted in improvement of asthma, and a recent study by Woodcock (35, 36). The observation that women had a lower physical and emotional sumscore is in line with other studies (21). The linear time trend was significant but the actual effect is negligible. The finding that the presence of asthma negatively influences quality of life is an extension and confirmation of an analysis on the baseline data of this set (20). We therefore conclude that further studies are warranted to evaluate the effects of environmental control in HDM-allergic patients.

Conclusion

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

The application of encasings does not have a beneficial effect on asthma, rhinitis or AEDS in subjects allergic to HDM as measured with the generic SF-36 questionnaire.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References

This project was supported by the Dutch Asthma Foundation, project number 32.98.14. The project was part of the Dutch Mite Avoidance Study (DUMAS) supported by a SGO grant. Authors are indebted to Ms S. A. Hendriks MD, Ms J. Broeshart MD, Ms A. J. van Oorschot-van Nes, Ms L. Havekes and Ms D. van der Naald for their invaluable contribution to the project. They also want to thank H. de Groot MD, PhD, for his valuable comments to earlier versions of this article.

References

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Patients
  5. End-points of the study
  6. Blinding and randomization procedures
  7. Statistical analysis
  8. Results
  9. General results
  10. Random regression modelling
  11. Discussion
  12. Conclusion
  13. Acknowledgments
  14. References
  • 1
    Custovic A, Chapman M. Risk levels for mite allergens. Are they meaningful? Allergy 1998;53: 7176.
  • 2
    Marks GB. House dust mite exposure as a risk factor for asthma: benefits of avoidance. Allergy 1998;53: 108114.
  • 3
    Kniest FM, Liebenberg B, Ahr A. Mattress-encasings as a barrier for mites and airborne dust. J Aerosol Sci 1992;23: S551554.
  • 4
    Kniest FM, Young E, VanPraag MC, Vos H, Kort HS, Koers WJ et al. Clinical evaluation of a double-blind dust-mite avoidance trial with mite-allergic rhinitic patients. Clin Exp Allergy 1991;21: 3947.
  • 5
    Tan BB, Weald D, Strickland I, Friedmann PS. Double-blind controlled trial of effect of housedust-mite allergen avoidance on atopic dermatitis. Lancet 1996;347: 1518.
  • 6
    Oosting AJ, De Bruin-Weller MS, Terreehorst I, Tempels-Pavlica Z, Aalberse RC, De Monchy JG et al. Effect of mattress encasings on atopic dermatitis outcome measures in a double-blind, placebo-controlled study: The Dutch mite avoidance study. J Allergy Clin Immunol 2002;110: 500506.
  • 7
    Cloosterman SG, Schermer TR, Bijl-Hofland ID, Van Der Heide S, Brunekreef B, Van Den Elshout FJ et al. Effects of house dust mite avoidance measures on Der p 1 concentrations and clinical condition of mild adult house dust mite-allergic asthmatic patients, using no inhaled steroids. Clin Exp Allergy 1999;29: 13361346.
  • 8
    Rijssenbeek-Nouwens LH, Oosting AJ, De Monchy JG, Bregman I, Postma DS, De Bruin-Weller MS. The effect of anti-allergic mattress encasings on house dust mite-induced early- and late-airway reactions in asthmatic patients. A double-blind, placebo-controlled study. Clin Exp Allergy 2002;32: 117125.
  • 9
    van der Heide S, Kauffman HF, Dubois AE, de Monchy JG. Allergen-avoidance measures in homes of house dust mite-allergic asthmatic patients: effects of acaricides and mattress encasings. Allergy 1997;52: 921927.
  • 10
    Terreehorst I, Hak E, Oosting AJ, Tempels-Pavlica Z, de Monchy JG, Bruijnzeel-Koomen CA et al. Evaluation of impermeable covers for bedding in patients with allergic rhinitis. N Engl J Med 2003;349: 237246.
  • 11
    Leynaert B, Neukirch F, Demoly P, Bousquet J. Epidemiologic evidence for asthma and rhinitis comorbidity. J Allergy Clin Immunol 2000;106: 201205.
  • 12
    Bousquet J, Duchateau J, Pignat JC, Fayol C, Marquis P, Mariz S et al. Improvement of quality of life by treatment with cetirizine in patients with perennial allergic rhinitis as determined by a French version of the SF-36 questionnaire. J Allergy Clin Immunol 1996;98: 309316.
  • 13
    Bousquet J, Bullinger M, Fayol C, Marquis P, Valentin B, Burtin B. Assessment of quality of life in patients with perennial allergic rhinitis with the French version of the SF-36 Health Status Questionnaire. J Allergy Clin Immunol 1994;94: 182188.
  • 14
    Bousquet J, Knani J, Dhivert H, Richard A, Chicoye A, Ware JE Jr et al. Quality of life in asthma: I. Internal consistency and validity of the SF-36 questionnaire. Am J Respir Crit Care Med 1994;149: 371375.
  • 15
    Molen vander T, Postma DS, Schreurs AJ, Bosveld HE, Sears MR, Meyboom de Jong B. Discriminative aspects of two generic and two asthma-specific instruments: relation with symptoms, bronchodilator use and lung function in patients with mild asthma. Qual Life Res 1997;6: 353361.
  • 16
    Kiebert G, Sorensen SV, Revicki D, Fagan SC, Doyle JJ, Cohen J et al. Atopic dermatitis is associated with a decrement in health-related quality of life. Int J Dermatol 2002;41: 151158.
  • 17
    Lundberg L, Johannesson M, Silverdahl M, Hermansson C, Lindberg M. Health-related quality of life in patients with psoriasis and atopic dermatitis measured with SF-36, DLQI and a subjective measure of disease activity. Acta Derm Venereol 2000;80: 430434.
  • 18
    Niemeijer NR, Fluks AF, de Monchy JG. Optimization of skin testing: II. Evaluation of concentration and cutoff values, as compared with RAST and clinical history, in a multicenter study [see comments]. Allergy 1993;48: 498503.
  • 19
    Niemeijer NR, Goedewaagen B, Kauffman HF, de Monchy JG. Optimization of skin testing: I. Choosing allergen concentrations and cutoff values by factorial design [see comments]. Allergy 1993;48: 491497.
  • 20
    Terreehorst I, Duivenvoorden HJ, Tempels-Pavlica Z, Oosting AJ, de Monchy JG, Bruijnzeel-Koomen CA et al. The unfavorable effects of concomitant asthma and sleeplessness due to the atopic eczema/dermatitis syndrome (AEDS) on quality of life in subjects allergic to house-dust mites. Allergy 2002;57: 919925.
  • 21
    Aaronson NK, Muller M, Cohen PD, Essink-Bot ML, Fekkes M, Sanderman R et al. Translation, validation, and norming of the Dutch language version of the SF-36 Health Survey in community and chronic disease populations. J Clin Epidemiol 1998;51: 10551068.
  • 22
    Keller SD, Bayliss MS, Ware JE Jr, Hsu MA, Damiano AM, Goss TF. Comparison of responses to SF-36 Health Survey questions with one-week and four-week recall periods. Health Serv Res 1997;32: 367384.
  • 23
    Ware JE Jr, Sherbourne CD. The MOS 36-item short-form health survey (SF-36): I. Conceptual framework and item selection. Med Care 1992;30: 473483.
  • 24
    Ware JE Jr, Keller SD, Gandek B, Brazier JE, Sullivan M. Evaluating translations of health status questionnaires. Methods from the IQOLA project. International Quality of Life Assessment. Int J Technol Assess Health Care 1995;11: 525551.
  • 25
    Ware JE Jr, Kemp JP, Buchner DA, Singer AE, Nolop KB, Goss TF. The responsiveness of disease-specific and generic health measures to changes in the severity of asthma among adults. Qual Life Res 1998;7: 235244.
  • 26
    Little GRD. Statistical analysis with missing data. New York: John Wilkey and Sons, 1987.
  • 27
    Akaike H. A new look at the statistical model identification. IEEE trans automat contr 1974;AC-19: 716723.
  • 28
    Schwarz G. Estimating the dimension of a model. Ann Stat 1978;6: 461464.
  • 29
    Beaumont F, Kauffman HF, de Monchy JG, Sluiter HJ, de Vries K. Volumetric aerobiological survey of conidial fungi in the North-East Netherlands: II. Comparison of aerobiological data and skin tests with mould extracts in an asthmatic population. Allergy 1985;40: 181186.
  • 30
    Tupker RA, DeMonchy JG, Coenraads PJ, Homan A, van der Meer JB. Induction of atopic dermatitis by inhalation of house dust mite. J Allergy Clin Immunol 1996;97: 10641070.
  • 31
    Cockcroft DW, Murdock KY, Kirby J, Hargreave F. Prediction of airway responsiveness to allergen from skin sensitivity to allergen and airway responsiveness to histamine. Am Rev Respir Dis 1987;135: 264267.
  • 32
    Guyatt GH, King DR, Feeny DH, Stubbing D, Goldstein RS. Generic and specific measurement of health-related quality of life in a clinical trial of respiratory rehabilitation. J Clin Epidemiol 1999;52: 187192.
  • 33
    Peroni DG, Boner AL, Vallone G, Antolini I, Warner JO. Effective allergen avoidance at high altitude reduces allergen-induced bronchial hyperresponsiveness. Am J Respir Crit Care Med 1994;149: 14421446.
  • 34
    Platts-Mills TA, Tovey ER, Mitchell EB, Moszoro H, Nock P, Wilkins SR. Reduction of bronchial hyperreactivity during prolonged allergen avoidance. Lancet 1982;2: 675678.
  • 35
    Gotzsche PC, Johansen HK, Burr ML, Hammarquist C. House dust mite control measures for asthma. Cochrane Database Syst Rev 2001;12: CD001187.
  • 36
    Woodcock A, Forster L, Matthews E, Martin J, Letley L, Vickers M et al. Control of exposure to mite allergen and allergen-impermeable bed covers for adults with asthma. N Engl J Med 2003;349: 225236.