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A systematic review and meta-analysis of interventions used to reduce exposure to house dust and their effect on the development and severity of asthma

C Macdonald, A Sternberg, and PR Hunter.

Review published: 2007.

CRD summary

The review assessed the effectiveness of household dust reduction interventions on the development or severity of asthma. The authors concluded that there was insufficient evidence of effectiveness in existing atopic disease, but that interventions from birth were useful in preventing diagnosed asthma. Limited study quality coupled with questionable data analysis methods, mean the authors' conclusions should be interpreted with caution.

Authors' objectives

To assess the effectiveness of household dust reduction interventions on the development or severity of asthma.


MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) were searched from inception to 2007 without language restrictions; search terms were reported. The Institute of Scientific Information database of global conference proceedings was searched from 2002.

Study selection

Randomised controlled trials (RCTs) that compared any household dust reduction intervention to a control group with placebo (where practical) or no intervention were eligible for inclusion if they provided a measurement of atopic disease. Studies that recruited known atopic participants needed to use either a clinical diagnosis or positive skin prick test to a known trigger allergen. Studies with antenatal participants had to have a first-degree relative with a clinical diagnosis of atopic disease (or disease confirmed by skin prick test). Eligible interventions were: allergen-impermeable bedding; household cleaning products/equipment; education programmes; and changes/repairs to the home environment.

Populations studied were either prenatally at high risk for atopy or were children or adults with asthma. Interventions aimed to achieve improvement or prevention and included use of allergen-impermeable bedding, vacuum cleaners or education, or were multicomponent in nature. Most control groups received no intervention. The main outcomes of interest included physician-diagnosed asthma, parent-reported wheeze and measures of lung function.

Two authors selected studies for inclusion. Disagreements were resolved via a third reviewer.

Assessment of study quality

Study quality was assessed using the Jadad scale (for a score out of 5). The criteria assessed were quality of randomisation, blinding and descriptions of withdrawals and drop-outs. The authors did not state how the validity assessment was performed.

Data extraction

Data were extracted to calculate relative risks (RR) for dichotomous outcomes or effect size for continuous outcomes, along with 95% confidence intervals (CI). It was unclear whether or not the effect sizes used were standardised.

The authors stated neither how data were extracted for the review nor how many reviewers performed the data extraction.

Methods of synthesis

Meta-analyses of pooled relative risks or effect sizes were performed using either random-effects or fixed-effect models. Heterogeneity was assessed using Cochran's Q. The authors reported that they tested for bias (but no further details were provided).

Results of the review

Fourteen studies were included in the review, although three were studies at different follow-up points of the same RCT population, which made the total sample size 4,536 participants (range 30 to 937). All trials scored 2 or 3 on the Jadad scale, with a mean of 2.4. Most studies were not blinded. Duration of follow-up ranged from six months to seven years.

Prevention of asthma: Interventions reduced levels of physician-diagnosed asthma (RR 0.79, 95% CI 0.66 to 0.94, p=0.009; five studies). There was no evidence of statistical heterogeneity. There were no significant changes in the levels of patient-reported wheeze (five studies). Significant heterogeneity was seen (p=0.005).

Improvement in diagnosed asthma: Intervention reduced the number of days ill with asthma (effect size -0.36, 95% CI -0.59 to -0.13, 2 studies) but did not improve lung function (three studies).

Authors' conclusions

There was insufficient evidence to suggest implementation of hygiene measures in an attempt to improve outcomes in existing atopic disease. Interventions from birth in those at high risk of atopy were useful in prevention of diagnosed asthma, but not parental-reported wheeze.

CRD commentary

The review addressed a clear question and was supported by appropriate inclusion criteria. Attempts to identify all relevant studies in any language were undertaken by searching electronic databases and conference proceedings. Suitable methods were employed to reduce the risks of reviewer error and bias for the process of study selection; the authors did not report on whether such methods were used to assess study quality and extract data, so the possibility of reviewer error and bias affecting these processes could not be ruled out. Assessment of study quality was limited to use of the Jadad scale, and results suggested most studies were not of good quality. Sufficient study details were provided and appropriate meta-analysis techniques appeared to have been used to pool the data. However, the authors did not report on what type of effect size was used for their analyses of continuous variables and heterogeneity tests were sometimes either not reported or not conducted. The use of a test for bias was also uninformative without further details reported. The interventions used in studies in the meta-analyses appeared to be diverse in nature and the study durations were varied. It was, therefore, questionable whether pooling in this way was the most appropriate method of synthesis. In light of both the quality of the included studies and the questionable methods used to pool the data, the authors' conclusions should be interpreted with caution.

Implications of the review for practice and research

Practice: See Authors' conclusions.

Research: The authors stated that it was necessary to standardise the reporting of results of studies of interventions aimed at reducing the severity of asthma symptoms.


Not stated.

Bibliographic details

Macdonald C, Sternberg A, Hunter PR. A systematic review and meta-analysis of interventions used to reduce exposure to house dust and their effect on the development and severity of asthma. Environmental Health Perspectives 2007; 115(12): 1691-1695. [PMC free article: PMC2137102] [PubMed: 18087584]

Indexing Status

Subject indexing assigned by NLM


Asthma /etiology /pathology /prevention & control; Dust /prevention & control; Environmental Exposure /prevention & control; Humans; Randomized Controlled Trials as Topic



Database entry date


Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.

CRD has determined that this article meets the DARE scientific quality criteria for a systematic review.

Copyright © 2014 University of York.

PMID: 18087584


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