Effects on patients with asthma of eradicating visible indoor mould: a randomised controlled trial

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.

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.

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).

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.