Modeling human health risks of airborne endotoxin in homes during the winter and summer seasons

Endotoxin, a component of gram-negative bacterial cell walls, is a pro-inflammatory agent that induces local and systemic inflammatory responses in normal subjects which can contribute to the risk of developing asthma and chronic obstructive lung diseases. A probabilistic approach linking models of exposure, internal dosimetry, and health effects was carried out to quantitatively assess the potential inhalation risk of airborne endotoxin in homes during the winter and summer seasons. Combining empirical data and modeling results, we show that the half-maximum effect of the endotoxin dose (ED50) was estimated to be 707.9 (95% confidence interval (CI): 308.8-1287.0) endotoxin units (EU) for body temperature change, 481.8 (95% CI: 333.2-630.3) EU for elevation of neutrophils, and 1174.5 (95% CI: 816.0-1532.9) EU for elevation of the cytokine, interleukin-6. Our study also suggests that airborne endotoxin in homes may pose potential risks, and a higher risk for elevation of neutrophils and cytokine interleukin-6 appeared in winter season than in summer. Our study offers a risk-management framework for discussion of future studies of human respiratory exposure to airborne endotoxin.