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House dust mite allergen in pillows

^a Wellington Asthma Research Group, Department of Medicine, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand

Correspondence to: Mr Siebers.

For many years asthmatic patients have been told to avoid using feather filled pillows on their beds, although there is no evidence to support this practice. Strachan and Carey's case-control study is the first to have directly challenged this assumption.¹ This study showed that, after exclusion of asthmatic subjects whose bedding had been changed because of their disease, pillows with synthetic fillings were a risk factor for severe asthma. In the light of this finding, we have compared pillows with synthetic and feather fillings for their content of Der p I, the major allergen of the house dust mite Dermatophagoides pteronyssinus.

Methods

and results

In December 1995 we took dust samples from nine pairs of pillows and analysed them for Der p I. Each pair consisted of one feather filled pillow and one filled with polyester fibre; these had been used together on the same adult bed for more than six months to ensure that the environmental exposures of the pillows in each pair were similar. The pillow fillings were encased in closely woven cotton fabric. Two of the subjects in our study slept with the polyester filled pillow on top, four with the feather filled pillow on top, and three had no preference. We took dust samples with a portable Hitachi CV-2500 vacuum cleaner with a sock attachment, vacuuming each pillow for three minutes on each side, a total of six minutes per pillow. We sieved the dust collected to remove fluff and large particles and weighed the resulting fine dust. We then analysed this dust for Der p I content using monoclonal antibody enzyme linked immunosorbent assay (ELISA).² The between batch coefficient of variation of the assay is <15% in our laboratory.

Levels of Der p I are usually given as µg Der p I per gram of fine dust. It is arguable that for pillows, which have direct contact with the head for several hours at a time, total Der p I is the important measure. We therefore measured total Der p I as well as µg Der p I/g fine dust for each pillow. We analysed the results with two-tailed paired Student's t tests after log transforming the data.

There was no significant difference in the total weights of fine dust obtained from polyester filled pillows (mean weight 0.065 g (95% confidence interval 0.021 g to 0.108 g)) and feather filled pillows (0.060 g (0.026 g to 0.145 g)). Table 1 shows the geometric means of the total weight of Der p I and µg Der p I/g fine dust obtained. Paired analysis showed that the polyester filled pillows contained significantly more total weight of Der p I (mean ratio 8.05 (95% confidence interval 1.69 to 38.2), P = 0.015) and significantly higher µg Der p I/g fine dust (mean ratio 3.57 (1.13 to 11.27), P = 0.034) than the feather filled pillows.

Table 1--Geometric means of total and relative weight of house
dust mite allergen Der p I in fine dust taken from pillows with
synthetic and feather fillings
----------------------------------------------------------------
                                                Mean ratio
                        Pillow filling
---------------------------------------------(95% confidence
                                           interval) of weights
                     Synthetic Feather     (synthetic: feather)
----------------------------------------------------------------
Weight of Der p I:
 Total (µg)          1.01     0.13      8.05 (1.69 to 38.2)
 Relative
  (µg/g fine dust)  22.28     6.24      3.57 (1.13 to 11.27)

Discussion

In New Zealand 81% of patients with severe asthma have a positive skin prick test to house dust mite allergen,³ and exposure to mite allergen is a factor in triggering attacks of asthma in asthmatic subjects.⁴ Strachan and Carey suggested that pillows with synthetic fillings may release volatile organic compounds which may influence the airway response to inhaled allergens.¹ While this may be true, they were perhaps assuming that the allergen load in feather fillings is as great or greater than that in synthetic fillings. Our results, and the fact that the differences are large enough to be detected with such a small sample, imply that this assumption is not valid. Further studies are needed to confirm our findings, and then to determine whether pillows with synthetic fillings preferentially retain allergen or support greater infestation with mites.

Funding: The Health Research Council of New Zealand.

Conflict of interest: None.

1. Strachan DP, Carey IM. Home environment and severe asthma in adolescence: a population based case-control study. BMJ 1995;311:1053-6. [Abstract/Free Full Text]
2. Luczynska CM, Arruda LK, Platts-Mills TAE, Miller JD, Lopez M, Chapman MD. A two-site monoclonal antibody ELISA for the quantification of the major Dermatophagoides spp. allergens Der p1 and Der f1. J Immunol Methods 1989;118:227-35. [Medline]
3. Stone L, Sawyer G, Tohill S, Miles J, Lewis S, Beasley R. Skin prick sensitivity to common allergens in patients admitted with acute asthma in Wellington hospitals [abstract]. Aust NZ J Med 1996 (in press).
4. Sporik R, Chapman MD, Platts-Mills TAE. House dust mite exposure as a cause of asthma. Clin Exp Allergy 1992;22:897-906. [Medline]

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