[Frontiers in Bioscience E4, 56-73, January 1, 2012]

Domestic endotoxin exposure and asthma in children: epidemiological studies

Donna Carole Rennie1,2, Joshua Allan Lawson2, Ambikaipakan Senthilselvan3, Philip James Willson2, James Arnold Dosman2

1College of Nursing, University of Saskatchewan, Saskatoon, Saskatchewan, Canada, 2Canadian Centre for Health and Safety in Agriculture, University of Saskatchewan, Saskatoon, Saskatchewan, Canada, 3Department of Public Health Sciences, School of Public Health, University of Alberta, Edmonton, Alberta, Canada

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Characteristics of endotoxin
3.1. What is endotoxin?
3.2. Endotoxin assay
3.3. Endotoxin and the response in the lung
3.4. Domestic endotoxin
3.4.1. Gram-negative sources
3.4.2. Collection of domestic endotoxin
3.4.3. Indoor environmental covariates of domestic endotoxin
4. Epidemiological studies
4.1. Background to epidemiological evidence
4.2. Cohort studies
4.3. Case control studies
4.4. Cross-sectional studies
4.5. Panel studies
5. Strengths and limitations of epidemiological studies
5.1. Measurement of endotoxin
5.1.1. Methods of sampling
5.1.2. Concentration or load? Selection of site in home for collection of vacuumed dust for endotoxin: Measuring respiratory outcomes
5.3. Assessing interactions
5.3.1. The role of atopy
5.3.2. Other environmental exposures
5.3.3. Gene environment interactions
6. Conclusions
7. Recommendations for future research
8. References

1. ABSTRACT

Homes contain low but measurable concentrations of endotoxin that have been linked to household conditions such as the presence of animals, smoking, crowding, and farm living. While endotoxin exposure in early life appears to have a protective effect for childhood asthma; the evidence from prospective cohort studies of young children suggests that endotoxin exposure contributes to early development of wheeze. Higher domestic endotoxin levels are linked to greater asthma severity in school age children unless children are farm residents where, higher doses of farm-related endotoxin seem to offer some protection against asthma. Currently there are inconsistencies between epidemiological studies examining the role of endotoxin and children's respiratory health that may be due, in part, to selection bias of study populations, timing between measurement of endotoxin levels and the assessment of asthma symptoms. Although there is good evidence to demonstrate that endotoxin exposure in homes is associated with wheeze in children, and less likely to be associated with asthma, understanding the mediating roles of atopy, genetic and other environmental factors requires further and extensive exploration.