Co-exposure to elevated levels of endotoxin from house dust and ambient air pollutants appears to have a synergistic impact on respiratory health, a US study suggests.
The study measured endotoxin levels from bedding and bedroom samples and average particulate matter (PM2.5), ozone and nitrous dioxide levels at the homes of 6,488 participants.
It found PM2.5, ozone and nitrous dioxide levels were positively associated with ER visits for asthma in the past 12 months even though the levels were well below the local air quality standards.
Co-exposure to elevated levels of house dust endotoxin and PM2.5 increased the odds of an ER visit for asthma five-fold (OR 5.01) compared to endotoxin alone (OR 1.98) or PM2.5 alone (OR 1.29).
The association applied equally to all participants or to children.
The researchers said in the AJRCCM that there were various mechanisms by which house dust endotoxin and ambient air pollutants might synergistically affect asthma outcomes.
“Simultaneous exposure to endotoxin and ambient air pollutants has been reported to synergistically produce oxygen free radicals in the lung through the activation of xanthine oxidase. This can cause acute lung injury with neutrophil influx and increased production of inflammatory cytokines,” they said.
“Post-exposure to ambient air pollutants may also increase endotoxin-induced production and storage of mucin glycoproteins and endotoxin-induced metaplasia.”