Endotoxin exposure-response relationships for various asthma phenotypes in dental healthcare workers

Introduction
In dental healthcare settings health teams are exposed to variable levels of airborne endotoxin concentrations from dental unit waterlines (DUWLs). Endotoxin exposures in various workplace settings have been shown to be an important predictor of the development and progression of occupational airways disease. The aim of this study was to characterise the endotoxin exposures in dental healthcare workers as well as the clinical endpoints of interest and to define the exposure-response relationships taking into consideration potential confounders.

Methods
A cross sectional study of dental healthcare workers in five academic dental institutions in South Africa was conducted. Personal air samples (n = 413) in various dental jobs were collected. A self-administered, modified ECRHS questionnaire eliciting the health and employment history was used to evaluate 454 subjects. Sera was analysed for atopic status, specific IgE to composite latex (k82) and to 8 recombinant latex proteins. Pre- and post-bronchodilator testing was conducted to assess airway reversibility. Multivariate logistic regression models were used to analyse for various outcomes in relation to exposure metrics.

Results
Cumulative endotoxin exposures (>51.12 EU/m3-year) was an important predictor of work-related ocular-nasal symptoms (OR = 3.82, 95% CI: 1.01 – 14.41) in non-atopic workers. Borderline significant associations were also observed between current airborne endotoxin concentrations (>5.83 EU/m3) and asthma-related symptoms (OR = 2.24, 95% CI: 0.97 – 5.17) as well as suboptimal lung function (FEV1<80% predicted) (OR = 8.02, 95% CI: 0.94 – 68.35) in non-atopic workers. Dental workers using latex gloves and concurrently exposed to low-grade elevated (> 5.83 EU/m3) endotoxin exposures were at increased risk (OR = 2.59, 95% CI: 1.20 – 5.60) of presenting with latex sensitisation.

Discussion
Endotoxin exposures from DUWLs play an important role in the manifestation of non-atopic asthma. Low-grade elevated endotoxin levels increase the risk of sensitisation to latex among dental healthcare workers using latex gloves.