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Quantitation of dust mites and allergen in small dust samples

1999; Elsevier BV; Volume: 104; Issue: 3 Linguagem: Inglês

10.1016/s0091-6749(99)70349-0

1097-6825

Larry G. Arlian, Marjorie S. Morgan, John F. Goelz,

Contact Dermatitis and Allergies

Exposure to mites and allergen involves multiple variables such as the concentration or quantity of allergen in each reservoir, the activity in the home that renders mite allergens airborne and inhalable, and the time an individual spends in areas with mite allergen. Central to exposure are the amounts of mites and allergen in each of the reservoirs in the home; hence it is critical that the best method of reporting these levels is used so that their relevance to sensitization and provocation of allergy symptoms can be evaluated and mite and mite allergen mitigation strategies can be used, if necessary. Mite and allergen levels have traditionally been reported as the number of mites or the amount of allergen per gram of dust collected by vacuum sampling of a finite surface area rather than by reporting the total mite or allergen content per sampled area. However, the total quantity of dust collected during sampling of a given surface area is greatly variable, yet it is important for evaluating exposure and identifying whether there is a mite allergen problem. In this study we investigated the total amount and concentration of mites and allergens on specific surfaces as well as the relationship between mite and allergen levels in various locations within homes. Dust samples were obtained from 19 homes in Houston, Tex, and from 24 homes in Dayton, Ohio, during July and August 1997 (high mite season). In each home dust was collected by vacuuming an upholstered couch or chair located in the family room and an unencased, regularly used mattress, pillow(s), and carpet next to the bed in the bedroom, as previously reported.1Arlian LG Bernstein D Bernstein IL Friedman S Grant A Lieberman P et al.Prevalence of dust mites in the homes of people with asthma living in eight different geographic areas of the United States.J Allergy Clin Immunol. 1992; 90: 292-300Abstract Full Text PDF PubMed Scopus (176) Google Scholar The entire surface of the pillows and 1 m2 of area of the other sites was vacuumed for 2 minutes to collect the sample. The number of mites (alive and dead) in a 50-mg aliquot of each sample was determined by our standard method.1Arlian LG Bernstein D Bernstein IL Friedman S Grant A Lieberman P et al.Prevalence of dust mites in the homes of people with asthma living in eight different geographic areas of the United States.J Allergy Clin Immunol. 1992; 90: 292-300Abstract Full Text PDF PubMed Scopus (176) Google Scholar If mattresses > pillows. Furthermore, there was no correlation between the mite densities in the various sampling sites (r 2 < 0.0032).Table ITotal number of mites (live + dead) per gram of dust or per total surface area of the pillow, total weight of pillow dust (in milligrams), and amount of allergen (nanograms of Dermatophagoides group 2 allergen [Der 2]) collected from 19 homes in Houston, Tex (subjects 01-19), and from 24 homes in Dayton, Ohio (subjects 21-44)SubjectsTotal mites/g dustPillow 1Pillow 2CouchBedroom carpetMattressNo. of mitesDust (mg)Der 2 (ng)No. of mitesDust (mg)Der 2 (ng)018030012063710611765511960240072040125964151155626203140600140738636270315514118604620880801366325112653550534020080472141330*ND063206801740509050236190166078606801480100795018594583185720848026016073352630190280920960138017118155120132102006201602218634871088496011380400607520723537116ND12100104014024298592924119ND13140608051235122904614607001207360818616204831554066018032545152614943740616220920900223681778329350136117120620204028692020371814040160694927821698026619601900420021169124389147211605240100120ND330ND2202020102011200232020402300NSNSNS24801600014810340ND256040120010NDNSNSNS26NS2016071142NDNSNSNS27140560300963NDNSNSNS2894010002601240NDNSNSNS29401600783ND671ND30NSNS140041ND181003120401600134NDNSNSNS323206020030NDNSNSNS33601801601140NDNSNSNS34120401601273288992NSNSNS35200NS203502375053638012080050ND320ND37180NS600500NSNSNS382205204801520NDNSNSNS390100100650NDNSNSNS40200NS281ND071ND41560NS500130NDNSNSNS42100640NS1320NDNSNSNS4390042020120NDNSNSNS444060NS140NDNSNSNS*Sample weight was not determined.ND, Der 2 was not determined; NS, no sample was collected. Open table in a new tab ND, Der 2 was not determined; NS, no sample was collected. The quantity of dust collected by thoroughly vacuuming the pillow surfaces in both Dayton and Houston was very small. The Houston pillows yielded a mean of 378 mg of dust. The mean total number of mites on these pillow surfaces was 136 ± 37 (range = 0 to 1007) with 27 of the 38 pillows (71%) having 2 μg of Der 2 allergen on the entire surface (mean = 662 ± 228 ng). Likewise, most pillow samples (27/32) from Dayton homes contained 10-year-old pillow contained 1273 mites. If this pillow is excluded as an outlier, the mean number of mites recovered from the remaining 31 pillows was 7 ± 2 with a range 0 to 71. Twenty-five of 32 pillows (78%) had fewer than 10 mites on their surfaces and all but this outlier had fewer than 75 mites per pillow surface (Table I). Our results indicate that mite breeding in specific sites in homes is independent of other sites and that dispersal of allergen from site to site does not result in a uniform distribution throughout the home. Therefore the levels of mite and allergen in one location within a home cannot be used to predict the levels in other areas or to determine occupant exposure to allergens. Most studies report mite and allergen density (concentration) as the amount per gram of collectable dust, although considerably less than 0.2 g of dust is usually recovered by vacuuming the entire pillow surface.2Frederick JM Warner JO Jessop WJ Enarder I Warner JA Effect of a bed covering system in children with asthma and house dust mite hypersensitivity.Eur Respir J. 1997; 10: 361-366Crossref PubMed Scopus (92) Google Scholar, 3Kemp TJ Siebers RW Fishwick D O’Grady GB Fitzharris P Crane J House dust mite allergen in pillows [letter].BMJ. 1996; 313: 916Crossref PubMed Scopus (66) Google Scholar, 4Hallum C Simpson B Houghton N Simpson A Craven M Custovic A et al.Mite allergens in feather and synthetic pillows [abstract 719].J Allergy Clin Immunol. 1999; 103: S188Google Scholar The practice of extrapolating and reporting dust mite and allergen concentrations per gram of dust when sampled areas or surfaces yield considerably less than 1 g of dust leads to the reporting of exaggerated mite and allergen levels on surfaces where there are few mites and little allergen. For example, one study2Frederick JM Warner JO Jessop WJ Enarder I Warner JA Effect of a bed covering system in children with asthma and house dust mite hypersensitivity.Eur Respir J. 1997; 10: 361-366Crossref PubMed Scopus (92) Google Scholar reported averages of 10.85 and 27.58 μg of Der p 1 per gram of dust on pillow surfaces from 2 cohorts of homes. However, the same data analyzed in terms of the actual dust collected per total pillow surface (0.084 and 0.063 g, respectively) resulted in means of 0.91 and 1.74 μg of Der p 1 for the entire surface. Another study3Kemp TJ Siebers RW Fishwick D O’Grady GB Fitzharris P Crane J House dust mite allergen in pillows [letter].BMJ. 1996; 313: 916Crossref PubMed Scopus (66) Google Scholar reported mean concentrations of Der p 1 of 22.28 and 8.24 μg/g, whereas the actual micrograms per pillow were 1.0 and 0.13 for synthetic and feather pillows, respectively. In our study, when the concentration was expressed per gram, 24 of 37 Houston pillows exceeded 100 mites per gram, yet only 2 pillows had > 1 g of collectable surface dust. Most had <0.5 g of dust (mean = 378 mg) and <100 mites on the entire surface. The results are even more striking for the Dayton pillows, where the mean number of mites per pillow was only 7 ± 2 (excluding 1 outlier) but extrapolated it was 137 mites per gram. Twenty-five of the 32 pillows had <10 mites on the entire pillow surface. On the basis of the data presented here and the few data reported in the literature, we are recommending that, as a standard, the actual number of mites and the total quantity of allergen be reported when less than 0.5 g of dust is collected from a sampled surface. For pillow surfaces the total mite number and allergen amount should be reported. We thank Camona Woodford and Dolores Rodriguez for helping to collect the dust samples and Jacqueline Neal, Christine Rapp, and DiAnn Vyszenski-Moher for performing the mite counts.