Within-Home versus Between-Home Variability of House Dust Endotoxin in a Birth Cohort Joseph H. Abraham,1,2,3 Diane R. Gold,1,2 Douglas
W. Dockery,1 Louise Ryan,1 Ju-Hyeong Park,4 and
Donald K. Milton1,2,5 1Harvard School of Public Health, Boston, Massachusetts, USA; 2Channing
Laboratory, Department of Medicine, Brigham and Women’s Hospital and
Harvard Medical School, Boston, Massachusetts, USA; 3Johns Hopkins
Bloomberg School of Public Health, Baltimore, Maryland, USA; 4Division
of Respiratory Disease Studies, National Institute for Occupational Safety
and Health, Morgantown, West Virginia, USA; 5University of Massachusetts
Lowell, Lowell, Massachusetts, USA Abstract Endotoxin exposure has been proposed as an environmental determinant of allergen responses in children. To better understand the implications of using a single measurement of house dust endotoxin to characterize exposure in the first year of life, we evaluated room-specific within-home and between-home variability in dust endotoxin obtained from 470 households in Boston, Massachusetts. Homes were sampled up to two times over 5-11 months. We analyzed 1,287 dust samples from the kitchen, family room, and baby’s bedroom for endotoxin. We fit a mixed-effects model to estimate mean levels and the variation of endotoxin between homes, between rooms, and between sampling times. Endotoxin ranged from 2 to 1,945 units per milligram of dust. Levels were highest during summer and lowest in the winter. Mean endotoxin levels varied significantly from room to room. Cross-sectionally, endotoxin was moderately correlated between family room and bedroom floor (r = 0.30) , between family room and kitchen (r = 0.32) , and between kitchen and bedroom (r = 0.42) . Adjusting for season, the correlation of endotoxin levels within homes over time was 0.65 for both the bedroom and kitchen and 0.54 for the family room. The temporal within-home variance of endotoxin was lowest for bedroom floor samples and highest for kitchen samples. Between-home variance was lowest in the family room and highest for kitchen samples. Adjusting for season, within-home variation was less than between-home variation for all three rooms. These results suggest that room-to-room and home-to-home differences in endotoxin influence the total variability more than factors affecting endotoxin levels within a room over time. Key words: dust endotoxin, endotoxin, intraclass correlation, variance components. Environ Health Perspect 113: 1516-1521 (2005) . doi:10.1289/ehp.7632 available via http://dx.doi.org/ [Online 5 July 2005] Address correspondence to D. Milton, Department of Work Environment, School of Health and Environment, University of Massachusetts-Lowell, 1 University Ave., Lowell, MA 01854 USA. Telephone: (978) 934-4850. Fax: (978) 452-5711. E-mail: Donald_Milton@uml.edu We thank D. Sredl for assistance with data management, the study research assistants, and especially the participants of the Home Allergens and Asthma Study. This study was supported by the National Institute of Environmental Health Sciences (NIEHS) grant R01 ES-07036 and NIEHS Center grant 2P30ES00002. J.H.A. received training support from National Institutes of Health/National Heart, Lung, and Blood Institute grant HL07427-23. The authors declare they have no competing financial interests. Received 1 October 2004 ; accepted 5 July 2005. The full version of this article is available for free in HTML or PDF formats. |