Seasonal variations in asthma impact the upper respiratory tract microbiome

The risk of asthma exacerbation after respiratory illness is notably increased in the fall when a specific network of bacteria colonizes the upper respiratory tract.

When specific networks of bacteria are present in the upper respiratory tract microbiome during respiratory illness, especially during a fall, the risk of an exacerbation is increased in children with asthma, according to a study published in the journal Journal of Allergy and Clinical Immunology.

Susan V. Lynch, PhD, and colleagues also found that interactions between specific bacterial networks and host gene expression increased the risk of exacerbation. “The seasonal variation in asthma exacerbations, with a marked increase in incidence in the fall, is a well-described phenomenon,” says Dr. Lynch. “This may be due to the seasonal dynamics of the upper respiratory tract microbiota. We further considered that season-specific interactions between discrete groups of upper respiratory tract microbes and epithelial gene expression may increase the risk of asthma exacerbation following fall respiratory disease. .

The study evaluated nasal samples from children (ages 6-17) with exacerbation-prone asthma who participated in the Mechanisms Underlying Asthma Exacerbations Prevented and Persistent With Immune-based Therapy (MUPPITS-1) trial. . Specimens were collected at a baseline visit and within 3 days of the onset of any symptoms of upper respiratory disease. For pathological events, the patient was considered to have an exacerbation if systemic corticosteroids or hospitalization were required.

Respiratory diseases and asthma exacerbations showed seasonal trends

Among the 208 children with asthma enrolled in MUPPITS-1, there were 164 respiratory illnesses and 143 asthma exacerbations, both of which showed seasonal patterns, with the highest incidence during the fall-winter seasons. The bacterial composition of the nasal microbiota varied seasonally in baseline and respiratory disease samples. In the spring, an increase Moraxella taxa was observed, while in the fall there was an increase Staphylococcus species.

Seasonal variation in fungal species was only found in disease samples, with enrichment for Malassezia and in the spring and for candidiasis and Cladosporium in autumn. Among disease samples, season-specific links to nasal microbiota, virus detection, and exacerbations were observed. During the fall, respiratory illnesses and subsequent exacerbations have been associated with members of the pathogenic bacterium Moraxella and Haemophilus, which were found to be enriched in patients with virus-positive respiratory disease and in those that progressed to exacerbations. Similar associations were not observed for other seasons. Additionally, neither baseline fungal composition nor disease was related to exacerbation risk.

“The airway microbiota is dynamic and exhibits seasonal dynamics,” says Dr. Lynch. “It is only when this aspect is taken into account in statistical models that the main microbial-host interactions related to the risk of asthma exacerbation following respiratory disease are discovered. Specifically, fall asthma exacerbations appear to be related to upper respiratory microbiota, while those experienced in other seasons appear to be due to other exposures. (Figure).”

Bacterial microbiota varied according to the age of the children

When examining the reference samples, the composition of the nasal bacterial microbiota differed by age. Older children had nasal enrichment of several Staphylococcus and Corynebacterium members, while younger children showed enrichment for Moraxella, Haemophilusand Allioococcus taxa. Bacterial composition of nasal microbiota at baseline was not correlated with time to respiratory illness, but was correlated with time to exacerbation.

Similarly, the fungal composition of the nasal microbiota varied with age. Malassezia taxon were associated with older children, whereas distinct members of Ascochyte, Malassezia, Cladosporiumand Verticillium were common in young children. Baseline fungal communities were not associated with time to first illness; however, the enrichment of Cladosporium operational taxonomic unit (OTU) 8 was associated with longer duration of respiratory disease.

“Our study shows that the risk of asthma exacerbation following respiratory disease is significantly increased in the fall when a specific network of co-associated bacteria, including Streptococcus and Hemophilus, colonizes the upper respiratory tract,” says Dr. Lynch. “This indicates that season-specific exposures can precipitate asthma exacerbations and that in the fall, bacterial colonization of the upper respiratory tract influences the risk of post-respiratory disease exacerbation in children aged school.”

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