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.”
“Likewise, initial exposure to ambient air pollutants can cause acute airway and lung injury and secondarily enable endotoxin to cross the epithelial barrier and exert toxic effects, causing the epithelial cells to produce inflammatory cytokines.”
They said children were particularly vulnerable due to the immaturity of their lungs and narrower airways.
Commenting on the research, Monash University’s Professor Michael Abramson and Associate Professor Yuming Guo said the findings were both biologically and epidemiologically plausible.
“We agree with the authors that further prospective cohort studies are needed to confirm whether similar interactions can be demonstrated in patients with other conditions such as chronic obstructive pulmonary disease, and would add bronchiectasis, cystic fibrosis and idiopathic pulmonary fibrosis,” they wrote in the journal.
“The confirmation of health effects at concentrations below current standards emphasises the importance of adequately protecting our patients with chronic lung diseases. If anything, after considering other recent studies, ambient air quality standards need to be further strengthened.”
They said strategies to reduce air pollution such as greater use of electric vehicles were warranted along with household measures to reduce endotoxin level such as cleaning, choice of flooring and keeping animals outside.
“At a time when some politicians appear determined to ignore the evidence and water down long standing protections to public health, demonstration of new interactions between indoor and outdoor air pollutants serve as an important reminder of how much still remains to be understood.”