At trial end, no overall differences in respiratory symptoms, lung function or quality of life were observed 1 year after children with moderate–severe asthma and HDM sensitisation were all given a mite-occlusive mattress cover and then received either feather upper bedding (pillow and quilt) or standard bedding care. This null finding could reflect a true lack of effect or other contributing factors may have produced a false negative result.
Statistical power was adequate to detect at least a 20% reduction in the risk of frequent wheeze and trial participant retention was high. Interventions for children with asthma that are possibly mediated through allergen reduction will appear ineffective if the type of asthma is not carefully characterised and children not sensitised to the putative allergen are included. However, here, 100% of trial participants were sensitive to one or both of the two HDM species tested at baseline and all had troublesome persistent asthma based on the level of symptoms required for entry into the study. Other components of the bedding environment may also have been influential. However, a high proportion of children in both groups slept on an occlusive mattress cover () and further adjustment for pillow and mattress cover types did not alter the findings. Asthma medication type and use did not differ between groups, and adjustment for this did not alter the results; therefore medication is unlikely to have contributed to these results. Differences in laundry practices may have contributed. Non-compliance with the use of feather bedding may have contributed to the null finding.
A quarter (27 of 94) of feather group children reported using synthetic pillows at trial end and one-third were not sleeping with the feather pillow and quilt (). Analysis by compliance rather than intention to treat raised the possibility that feather bedding use was associated with reduced respiratory symptoms and better lung function, a result in line with the observational epidemiological findings.1–6 15 23 26 27
However, this analysis by compliance is not conclusive because it suffers from the same potential selection bias problem as the observational studies in those children with more severe asthma who may have been less likely to maintain feather bedding use.
This study found that child sleep position influenced bedding–wheeze associations, with a protective effect of feather bedding being observed in children who slept in the supine but not the prone position. Although based on small numbers, this issue was examined a priori and the findings are consistent with previous observations that among children who slept supine, feather quilt use was associated with less frequent wheeze compared with synthetic quilt use.14
Thus, it is also possible that an interactive effect between sleep position and the bedding–wheeze association may have contributed to the null result when all sleeping positions are combined together.
Environmental Der p 1 aeroallergen levels did not differ significantly between the groups. However, both groups received mattress encasings which constituted at least some intervention and, consistent with the intention of the trial, no other measures such as regular laundry were additionally used.
In the high mite environment of Sydney, surface allergen may have accumulated similarly from non-bedding sources onto both types of bedding. In this environment, additional interventions such as frequent washing of bedding or the use of air filters could be evaluated.
Finally it should be noted that the findings from this study pertain to children with asthma and HDM sensitisation, not the child population generally. Thus a null result from this therapeutic intervention does not rule out a potential protective effect of feather bedding in relation to the inception of asthma.
In conclusion, no differences in respiratory symptoms or lung function were observed 1 year after children with moderate–severe asthma and HDM sensitisation were all given a mite-occlusive mattress cover and then received either feather upper bedding (pillow and quilt) or standard bedding care. The findings have implications for the policy and the design of future trials of bedding interventions for child asthma. These findings do not provide support for previous recommendations that feather bedding should be avoided for children with asthma.15
Child sleep position should be considered in the design phase and a pre-RCT washout period, to detect if parents will comply with the bedding intervention, may also be required. The potential benefit of upper bedding interventions in childhood asthma necessitates that further evaluations be undertaken with an emphasis on maintaining long-term compliance, additionally considering sleep position and focusing on the micro environment immediately adjacent to the airway of the sleeping child.