Linking endotoxin to asthma severity through personal exposure assessment
A paper was recently published (JACI; Rabinovitch et al., November, 2005) that demonstrated for the first time a significant association between breathing zone endotoxin exposures and asthma severity in children. This relationship, however was not observed with indoor fixed-location monitoring. While this associative finding by itself was precedent setting, the underlying advances in personal exposure science that made this finding possible have been substantial. This presentation will address the rationale and science behind recent key elements that have advanced the characterization of personal aerosol exposure to environmental triggers of asthma worsening, including endotoxin and environmental tobacco smoke.
At the outset, it was obviously critical that an accurate personal aerosol monitoring system was needed of sufficiently low burden to be carried by small, elementary-age children for 24 hr periods in a longitudinal study framework. It became clear that faithful protocol compliance (actually wearing the monitor) was critical for species such as endotoxin that are elevated in the inhaled personal cloud due to source proximity. The periods when the monitor were not worn effectivelyreduced the strength of the associations (exposures to health outcomes), as the monitor then became a fixed-location sampler. Also important was the ability to identify the associated level of environmental tobacco smoke (ETS) exposure. Not only did the presence of ETS violate the study protocol, the aqueous extraction efficiency of the endotoxin from the Teflon exposure sampler filter was reduced with large ETS contributions, potentially affecting the accuracy of the endotoxin analyses. The reduced extraction efficiency also stressed the capability of the endotoxin assay for the already-small sample collections provided by low-flowrate personal exposure samples.
Information will be presented on key design features of the personal exposure sampler, the compliance monitoring system, and non-destructive identification of the contribution of ETS to the aerosol collections. The exposure data will be discussed, along with a summary of the supporting data from these sampling system component/supporting devices will be discussed. A new technology ultra-miniature (<200g) personal aerosol exposure technology being developed for future childrens' personal exposure studies will also be highlighted that should enhance compliance and permit more robust longitudinal designs.