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Effects on patients with asthma of eradicating visible indoor mould: a randomised controlled trial
  1. M L Burr,
  2. I P Matthews,
  3. R A Arthur,
  4. H L Watson,
  5. C J Gregory,
  6. F D J Dunstan,
  7. S R Palmer
  1. Department of Epidemiology, Statistics and Public Health, Cardiff University, Cardiff, UK
  1. Correspondence to:
    Dr M L Burr
    Department of Epidemiology, Statistics and Public Health, Neuadd Meirionnydd, Heath Park, Cardiff CF14 4YS, UK; burrml{at}


Background: It is not clear whether associations between respiratory symptoms and indoor mould are causal. A randomised controlled trial was conducted to see whether asthma improves when indoor mould is removed.

Methods: Houses of patients with asthma were randomly allocated into two groups. In one group, indoor mould was removed, fungicide was applied and a fan was installed in the loft. In the control group, intervention was delayed for 12 months. Questionnaires were administered and peak expiratory flow rate was measured at baseline, 6 months and 12 months.

Results: Eighty-one houses were allocated to the intervention group and 83 to the control group; 95 participants in 68 intervention houses and 87 in 63 control houses supplied follow-up information. Peak expiratory flow rate variability declined in both groups, with no significant differences between them. At 6 months, significantly more of the intervention group showed a net improvement in wheeze affecting activities (difference between groups 25%, 95% CI 3% to 47%; p = 0.028), perceived improvement of breathing (52%, 95% CI 30% to 74%; p<0.0001) and perceived reduction in medication (59%, 95% CI 35% to 81%; p<0.0001). By 12 months the intervention group showed significantly greater reductions than the controls in preventer and reliever use, and more improvement in rhinitis (24%, 95% CI 9% to 39%; p = 0.001) and rhinoconjunctivitis (20%, 95% CI 5% to 36%; p = 0.009).

Conclusions: Although there was no objective evidence of benefit, symptoms of asthma and rhinitis improved and medication use declined following removal of indoor mould. It is unlikely that this was entirely a placebo effect.

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  • Funding was received from Asthma UK (grant number 01/025), the Medical Research Council (grant number G9900679) and the Welsh Office of Research and Development (grant number S01/001).

  • Competing interests: None declared.

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