Microbiome of upper airway could affect asthma severity

There may be a link between bacteria that live in the upper airway and the severity of asthma symptoms among children with mild to moderate asthma, according to a new study published in the journal Nature Communications.

The study was conducted in conjunction with a clinical trial involving 214 children ages 5 to 11 with mild to moderate asthma. The trial, called Step Up Yellow Zone Inhaled Corticosteroids to Prevent Exacerbations, was conducted as part of AsthmaNet, a national network of medical centers conducting asthma research funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health.

The clinical trial's purpose was to determine whether quintupling the dose of an inhaled corticosteroid at the first signs of worsening asthma was better than keeping a low dose of the same medication. The trial found no benefit to the larger dose, and those results were published in The New England Journal of Medicine in 2018.

During that trial, the researchers also collected nasal mucus samples from the children to study their upper airway microbiomes. Samples were collected at the beginning of the trial, when all the participants had controlled asthma, as well as at the first early signs that asthma control was slipping.

The researchers found that children who experienced early warning signs that their asthma was going to flare up were more likely to have bacteria associated with disease, including Staphylococcus, Streptococcus, and Moraxella bacterial groups, living in their upper airways. In contrast, airway microbes dominated by Corynebacterium and Dolosigranulum bacteria were associated with periods of good health, when asthma was well-controlled.

In the study, researchers also found  that children whose airway microbial communities switched from being dominated by Corynebacterium and Dolosigranulum bacteria to being dominated by Moraxella bacteria were at the highest risk of worsening asthma symptoms compared with children whose microbial communities made any other kind of shift.

In the U.S., more than 6 million children under age 18 have asthma, or about one in 12. It is the leading chronic pediatric disease and the top reason for missed school days, according to the Asthma and Allergy Foundation of America.

Based on the results, the researchers said they plan to conduct studies in mice with carefully controlled airway microbiomes to see if the researchers can uncover a causal role for bacteria in asthma severity. In addition, such experiments could allow them to test different interventions that might deliberately alter the upper airway bacteria in a way that could be protective.