Indoor pest allergens associated with upper respiratory infections
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Key takeaways:
- Mouse allergens were associated with infections plus reduced lung function and eosinophilic inflammation.
- Disparities in these infections may drive disparities in asthma exacerbations.
WASHINGTON — Concentrations of indoor pest allergens were consistently associated with upper respiratory infections, according to an abstract presented at the American Academy of Allergy, Asthma & Immunology Annual Meeting.
These concentrations also may contribute to disparities in asthma exacerbations, Darlene Bhavnani, PhD, MPH, infectious disease epidemiologist, department of population health, Dell Medical School at the University of Texas at Austin, said during her presentation.
Disparities in asthma, allergen exposure
“The racial and ethnic disparities in asthma morbidity are very well documented by now, but the underlying causes of these disparities are not,” Bhavnani said.
However, Bhavnani noted that upper respiratory infections are major triggers for asthma exacerbations.
“If there are these racial and ethnic disparities in asthma exacerbations, and many of these exacerbations are triggered by viruses, what role then do these viruses play in the disparities we see?” she said.
Using a nationally representative survey, Bhavnani and her colleagues found that Black and Mexican American children of school age with asthma were twice as likely to report upper respiratory infections as white children of the same age with asthma.
“It’s possible, with this in mind, that the racial disparities that we see in upper respiratory viral infection may help to explain the disparities in asthma exacerbation,” Bhavnani said.
But this hypothesis led the researchers to question what drives these racial and ethnic differences in upper respiratory infections and whether contextual factors may increase susceptibility to these infections.
“What we do know is that communities of color are more commonly exposed to indoor pest allergens, both in the home and at school, and are more often sensitized to these allergens,” Bhavnani said.
Allergen exposure also could impair viral defense mechanisms, she added.
Study design, results
“That raises the next question of whether indoor allergens actually affect one’s susceptibility to upper respiratory infection,” Bhavnani said.
The researchers investigated whether exposure to higher concentrations of indoor allergens was associated with four outcomes:
- having an upper respiratory infection;
- having an upper respiratory infection with cold symptoms;
- having an upper respiratory infection, cold symptoms and pulmonary eosinophilic inflammation, defined as fractional exhaled nitric oxide higher than 20 ppb; and
- having an upper respiratory infection, cold symptoms and reduced lung function, defined as percent predicted FEV1 of less than 80%.
The researchers included eosinophilic inflammation and reduced lung function because they are commonly associated with asthma exacerbations, Bhavnani said.
Data came from 90 children (60% boys; 92% Black; 92% using public insurance) with persistent asthma who participated in the Environmental Control as Add-on Therapy for Childhood Asthma study, conducted in 2017 and 2018.
“They were all atopic, so they had some sensitization to indoor allergens,” Bhavnani said.
The study included clinic visits at baseline and months 0, 2, 4 and 6, with spirometry and FeNO measurements. Also, nasal mucus samples were tested for rhinovirus, respiratory syncytial virus, influenza, coronavirus, adenovirus, parainfluenza and human metapneumovirus.
During home visits at baseline and months 3 and 6, the researchers collected air and floor dust samples from the children’s bedrooms. The air samples were tested for mouse allergen, and the dust samples were tested for cockroach, cat and dog allergen.
“Each one of our participants was observed between one and three times,” Bhavnani said.
The 191 observations detected respiratory virus 27% of the time.
Concentrations of mouse allergen were associated with symptomatic upper respiratory infections (OR = 1.24; 95% CI, 0.9-1.72), upper respiratory infections plus reduced lung function (OR = 1.58; 95% CI, 1.1-2.27) and upper respiratory infections plus pulmonary eosinophilic inflammation (OR = 1.42; 95% CI, 0.98-2.04).
“Odds ratios are all greater than one,” Bhavnani said. “With the increasing severity of outcome, we see the increasing strength of the association.”
Similarly, concentrations of cockroach allergen were associated with symptomatic respiratory infection (OR = 1.3; 95% CI, 0.98-1.71) and upper respiratory infection plus reduced lung function (OR = 1.79; 95% CI, 1.05-3.03).
“A doubling in cockroach allergen concentration actually increased the odds of an upper respiratory infection with colds by about 20%,” Bhavnani said.
Additionally, doubling of cockroach allergen concentrations increased odds for upper respiratory infection, colds and eosinophilic inflammation by about 30%, she continued.
“And it increased the odds of an upper respiratory infection, cold and reduced lung function by about 45%,” Bhavnani said. “As these end points increase in severity, so does the strength of the odds ratio.”
The results for cat and dog allergen were inconsistent, the researchers said.
When the researchers examined whether there were differences between the children who were sensitized to indoor allergens and those who were not, they found stronger associations among the children who were sensitized to cockroach and mouse, but again, not necessarily to cat and dog.
Bhavnani also cautioned that these differences are not necessarily statistically significant and that the study had several limitations.
“These were low concentrations of allergens and a moderate sample size that might have limited our ability to detect many associations,” she said.
Also, the researchers tested for rhinovirus A and B but not C.
“Rhinovirus C is actually associated with asthma exacerbations that are commonly found in children with upper respiratory infection, so this could have actually led to some misclassification of our outcomes,” Bhavnani said.
Still, she continued, failure to detect rhinovirus C most likely would lead to a bias toward the null, making the odds ratios derived from this study more conservative.
“Finally, data were collected from a low-income and Black population in a single inner-city setting,” Bhavnani said. “This potentially limits the generalizability of our findings to other populations.”
Conclusions, next steps
Based on these findings, the researchers concluded that there were consistent associations between concentrations of indoor pest allergens and upper respiratory infections including upper and lower respiratory symptoms.
Also, they said, these differences in concentrations of pest allergens may add to the disparities in the risks for experiencing upper respiratory infections, upper respiratory symptoms and, subsequently, viral-associated asthma exacerbations.
“Multiracial and multiethnic cohort studies are really needed with sufficient power to further investigate this hypothesis,” Bhavnani said.
While this study looked at the impact of viral infections on these disparities, bacterial infections may have a role too, Bhavnani said.
“It’s quite possible that these bacterial communities differ between those living in areas and homes that are disadvantaged compared to other communities,” she said.
“It would be interesting to look at the impact of microbes in the environment as well as the normal microbiota that someone carries to see whether they affect some of the results that we’re seeing,” she said.