Variation of Endotoxin Concentrations by Location within Homes

Abstract

RATIONALE: Multiple studies have reported on relationships between home endotoxin exposure and subsequent allergic risk but little is known about the variation of endotoxin within homes. METHODS: We studied the homes of a geographically-based birth cohort of 249 infants. Dust samples were obtained from 5 locations in each home when the infants were 1 month old and in 98 homes when the infants were 6 months old. Endotoxin was measured in eluted dust samples with a recombinant factor C assay and expressed as endotoxin units (EU) per mg of dust. The data were analyzed to learn how well concentrations correlated between locations within homes and whether the concentrations changed over time. RESULTS: The mean endotoxin levels were 3.58, 15.6, 19.1, 4.71, and 15.5 EU/mg for the child's bed, child's bedroom floor, living room floor, mother's bed and mother's bedroom floor, respectively. Correlations of the concentrations between the 5 locations ranged from .24 to .59 and while modest all correlations were significant (p<0.001). However, of the 10 possible pair-wise comparisons of the endotoxin concentrations by location, all differed significantly (P<0.05) except for the pair of the child's and mother's bedroom floors (P=0.99). Comparison of the 1 and 6 month values in 98 homes showed a significant increase from 3.32 to 5.42 EU/mg (p=0.001) in the child's bed but no other significant changes. CONCLUSIONS: There are large variations in endotoxin concentration between different locations within homes suggesting that one endotoxin measurement from a single site provides limited information concerning endotoxin exposure.