Clinical Epidemiology Unit

Does ecasing bedding reduce house dust mite allergen and improve asthma in allergic asthmatics?

Dr Shyamali Dharmage
Assoc Prof Michael Abramson
Dr Nick Freezer
Dr Frank Thien
Prof Haydn Walters

Funded by: Department of Human Services

The efficacy of encasement of bedding in the control of house dust mite allergens and asthma is controversial.
Aim: To evaluate the impact of encasement of bedding with impermeable covers on asthma outcomes in mite sensitised adults.
Methods: A group of 33 young adults with current asthma and positive skin tests to house dust mite were randomised into either an intervention group whose pillows, mattresses and doonas were encased with impermeable covers, or a control group who received cotton covers. Before and, 3 and 6 months after encasement, dust samples were collected from the bedding and assayed for Der p 1. Clinical outcomes included quality of life, lung function, bronchial hyper-reactivity to methacholine, symptoms, medications and peak flow rates. Differences between groups were examined using repeated measures analysis of variance. 
Results: Baseline Der p 1 levels in both active and placebo groups were comparable and high (19.2 Vs 18.2 mcg/g of dust). There was a significant reduction in Der p 1 levels in the active group from 19.2 to 7.2 mcg/g of dust, but not in the placebo group. Quality of life improved in both the intervention and control groups, but there was no significant difference in the improvements between the groups. There was no significant change in FEV1, FVC, PD20, daytime or nocturnal symptoms, requirements for reliever or preventer medications, or peak flows.
Conclusions: Encasement of bedding was found to significantly reduce the Der p 1 levels, but this reduction was not sufficient to produce worthwhile clinical improvement among adults with asthma who were sensitised to house dust mites.

Publications:

Dharmage S, Bailey M, Raven J, Cheng A, Thien F, Rolland J, Abramson M, Walters EH. Residential characteristics influence the Der p1 levels in Melbourne homes. Clin Exp Allergy 1999;29:461-469.

Dharmage S, Bailey M, Raven J, Mitakakis T, Cheng A, Rolland J, Guest D, Thien F, Abramson M, Walters EH. A reliable and valid home visit report for studies of asthma in young adults. Indoor Air 1999;10:188-92.

Dharmage SC, Bailey M, Raven J, Mitakakis T, Thien FCK, Forbes AB, Guest D, Abramson M, Walters EH. Prevalence and residential determinants of fungi within homes in Melbourne, Australia. Clin Exp Allergy 1999; 29:1481-90.

Dharmage S, Bailey M. et al. Seasonal variation in level of Der p 1 and fungi in Melbourne homes. Respirology 1999; 4(S):A19.

Dharmage SC, Bailey M, Wharton C, Raven J, Cao D, Rolland J, Thien F, Light L, Freezer N, Walters EH. Does encasement of bedding improve asthma in atopic adults with asthma? Respirology 2000;5(Suppl):A13