| Home Endotoxin Exposure and Wheeze in Infants: Correction for Bias Due to Exposure Measurement Error Nora Horick,1 Edie Weller,1 Donald K. Milton,2,3 Diane R. Gold,2,3 Ruifeng Li,4 and Donna Spiegelman1,4 1Department of Biostatistics, and 2Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA; 3Channing Laboratory, Harvard Medical School, Boston, Massachusetts, USA; 4Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA Abstract
Exposure to elevated levels of endotoxin in family-room dust was previously observed to be significantly associated with increased wheeze in the first year of life among a cohort of 404 children in the Boston, Massachusetts, metropolitan area. However, it is likely that family-room dust endotoxin was a surrogate for airborne endotoxin exposure. Therefore, a related substudy characterized the relationship between levels of airborne household endotoxin and the level of endotoxin present in house dust, in addition to identifying other significant predictors of airborne endotoxin in the home. We now reexamine the relationship between endotoxin exposure and wheeze under the assumption that the level of airborne endotoxin in the home is the exposure of interest and that the amount of endotoxin in household dust is a surrogate for this exposure. We applied a measurement error correction technique, using all available data to estimate the effect of endotoxin exposure in terms of airborne concentration and accounting for the measurement error induced by using house-dust endotoxin as a surrogate measure in the portion of the data in which airborne endotoxin could not be directly measured. After adjusting for confounding by lower respiratory infection status and race/ethnicity, endotoxin exposure was found to be significantly associated with a nearly 6-fold increase in prevalence of wheeze for a one interquartile range increase in airborne endotoxin (95% confidence interval, 1.2-26) among the 360 children in households with dust endotoxin levels between the 5th and 95th percentiles. Key words: asthma, endotoxin, measurement error, regression calibration, wheeze. Environ Health Perspect 114:135-140 (2006) . doi:10.1289/ehp.7981 available via http://dx.doi.org/ [Online 12 August 2005]
Address correspondence to D. Spiegelman, Department of Epidemiology, Harvard School of Public Health, 677 Huntington Ave., Boston, MA 02115 USA. Telephone: (617) 432-0205. Fax: (617) 566-7805. E-mail: stdls@channing.harvard.edu We thank K. McGaffigan and D. Sredl for assistance with data management and analysis, and the research assistants who collected questionnaire information and dust and air samples and who assayed samples. We especially thank the caregivers of the children who participated in the study. This work was supported by National Institute for Environmental Health Sciences (NIEHS) grant R01 ES-07036, National Institute of Allergy and Infectious Diseases/NIEHS grant R01 AI/EHS-35786, and NIEHS Center grant 2P30ES00002 and by a gift from BioWhittaker (Walkersville, MD) . The authors declare they have no competing financial interests. Received 31 January 2005 ; accepted 11 August 2005.
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