In a recent study published in The Lancet Microbe, researchers conducted a systematic review to assess the association between infant gut microbiota composition and childhood respiratory disorders.
Study: the association between early life gut microbiota and childhood respiratory disease: a systematic review. Image credit: Orawan Pattarawimonchai/Shutterstock
background
Childhood respiratory disorders such as asthma and recurrent wheezing have caused considerable mortality and morbidity among children. Previous studies using animal models have reported on the role of the infant gut microbiota in lung immunological development and in establishing vulnerability to asthma and respiratory infections in humans.
About the study
In the present study, the researchers systematically reviewed the existing literature to explore the association between the composition of the gut microbiome in infancy (less than one year of age) as measured by genomic sequencing and the development of childhood respiratory disorders such as respiratory infections, asthma or recurrent wheezing.
The systematic review was conducted following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Data were obtained from databases such as Cochrane, MEDLINE, Web of Science, Scopus and Embase for full-text articles in English published between 1 January 2010 and 27 April 2021, using terms of search such as gut, childhood, respiratory disease and microbiota.
For in vitro-type studies, if they included non-primary research, or if the outcome exposure was irrelevant to the primary research question, they were excluded from the systematic review. Two reviewers examined and critically appraised the data independently, and a third reviewer resolved disagreements. We assessed the methodological quality of all studies, using the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) checklist for metagenomic data and the NOS (Newcastle-Ottawa Scale) for ‘bias assessment.
results
A total of 7347 studies were initially identified from the databases and one potentially eligible study from other sources, from which 2589 duplicate articles were excluded. Of the remaining 4759 titles and abstracts selected, 4648 were excluded based on the eligibility criteria. As a result, we assessed the full text of 111 studies and excluded 100 studies.
The reasons for exclusion were: (i) they were not peer-reviewed or original research (n=42), (ii) in vitro studies (n=7), (iii) the infant gut microbiome was not exposure (n=17). ), (iv) the outcome was not respiratory disease (n=17), (v) the gut microbiome was not assessed before the onset of respiratory disease (n=7), (vi) the gut microbiome was first assessed after 1 year of age (n = 2), (vii) microbiome was not assessed by next-generation sequencing, or (viii) small patient subset (n = 5), sample size below five participants (n = 3).
Finally, 11 studies were considered for the systematic review including cohort studies (n=8) and case-control studies (n=3) and the average sample size across studies comprised 319 individuals. 16S ribosomal ribonucleic acid (rRNA)-targeted amplicon sequencing was performed in all studies to determine the gut microbiome. Four studies, one study and six studies were of poor quality, fair quality and good quality, respectively.
Two (of seven) studies reported that a greater α-diversity gut microbiota during the first 12 months of age was significantly associated with absence of atopic wheezing at 1 year of age and absence of asthma at five or six years of age. One study reported a positive association between the maturity of the gut microbiome at five weeks of age and the risk of asthma among children aged six to eleven. In contrast, two of the included studies reported that an immature gut microbiome at one year of age was associated with an increased risk of asthma at five or six years.
In addition, an association was observed between lower abundance of Lachnospira at three months of age, but higher abundance of Lachnospira at one year of age and atopic wheezing and asthma between one and six years of age. One study showed similar associations for Veillonella species, while two studies reported the opposite.
An association was observed between higher abundance of Rhodotorula and Candida and lower abundance of Malassezia at one month of age and higher abundance of Pichia kudriavzevii at three months of age and atopic wheezing and asthma at four or five years of age. age However, another study found no such associations. One study demonstrated a higher incidence of lung disorders at one year of age in cases of lower Bifidobacterium abundance and higher Enterococcus and Klebsiella abundance at one week of age.
The results of the study were heterogeneous; however, in general, a lower abundance of Bifidobacterium species in stool samples obtained between one and three months of age and a lower abundance of Faecalibacterium, Roseburia and Ruminococcus species in stool samples obtained between three months and one year of age were associated with atopic wheezing and asthma between one and six years.
Overall, the study results demonstrated an association between low α-diversity and the abundance of specific gut microbiota (Faecalibacterium, Bifidobacterium, Roseburia and Ruminococcus) with respiratory diseases in childhood. However, results were inconsistent and further research with larger sample populations and standardized and uniform outcomes, follow-up periods, and analysis tools is warranted to identify targets for preventing childhood respiratory disease.