Previous research has shown that disruptions in maternal or infant gut microbiota may contribute to adverse outcomes such as preterm birth, gestational diabetes, and maternal obesity. Now, new evidence from a large-scale Finnish cohort study suggests that subtle differences in the gut microbiota of mothers and their babies could signal a higher risk of respiratory tract infections (RTIs) in early life. The findings, published in Pediatric Research, highlight the potential for microbiota-based strategies to strengthen infant immunity.
Respiratory infections are among the most common illnesses in infancy. Even healthy, full-term babies typically experience four to ten episodes in their first year. While many infections are mild, they can disrupt family life, cause missed work for parents, increase healthcare visits, and in some cases require urgent care. Scientists have long suspected that the gut microbiome, a complex community of microorganisms in the digestive tract, plays a role in shaping immune defense. Animal studies have hinted at this connection, but human data have been inconsistent.
The new study is based on the population-based Helsinki cohort, which included more than 1,000 full-term, normal-weight infants. Among them, 18% developed at least one RTI requiring medical attention within the first six months. To probe microbial links, researchers conducted a nested case-control study of 178 infants with RTIs and 143 controls, along with fecal samples from 136 mothers of affected infants and 125 mothers of controls. Families kept detailed weekly online diaries of symptoms and medical visits, providing unusually precise documentation. Stool samples were collected from mothers at delivery and from infants at three and six weeks of age, then analyzed using 16S rRNA sequencing.
The results showed major differences in microbial composition. Mothers of infants who developed RTIs had higher levels of opportunistic bacteria such as Citrobacter, Enterobacter, and Enterococcus, but lower levels of Clostridium. This pattern points to maternal microbial instability as a potential independent risk factor.
In infants, overall microbial diversity did not predict RTI risk, but specific bacterial signatures did. At three weeks, those who later developed RTIs had higher levels of families such as Rikenellaceae, Prevotellaceae, and Verrucomicrobiaceae, and genera including Alistipes, Akkermansia, Faecalibacterium, Peptoniphilus, and Serratia. By six weeks, persistent elevation of Prevotellaceae and reduced abundance of Anaerostipes, a butyrate-producing genus linked to gut balance and immune regulation, were observed. Sensitivity analyses reinforced these associations, revealing higher levels of other butyrate producers (Pseudobutyrivibrio, Faecalibacterium, Roseburia) and Proteus, along with lower Veillonella and Anaerostipes.
Clinically, about one-third of RTIs occurred in the first three months of life, with ear infections (otitis media) dominating this period. The median illness lasted 11 days, nearly half of infants required medical consultation, and 14% needed emergency care. The findings underscore the substantial health burden of RTIs even in otherwise healthy populations.
One major observation was that nearly all infants in the cohort were breastfed, which resulted in high levels of Bifidobacterium; however, RTIs still occurred. This suggests that while Bifidobacterium is beneficial, other bacterial groups and the timing of microbial development may be equally critical. Early appearance of adult-type butyrate producers such as Faecalibacterium and Roseburia could represent “premature microbiota maturation,” paradoxically increasing vulnerability to infection.
The current findings add to mounting evidence that maternal and infant microbiota play a crucial role in shaping early immune resilience. Although more research is needed to confirm mechanisms, the study points toward future preventive strategies, including maternal microbiota modulation or targeted probiotics, that could reduce the risk of respiratory infections during a baby’s most vulnerable months.
Reference
Hyvönen S, Saarikivi A, Mälkönen J, Solasaari T, Korpela K, de Vos WM, et al. The association of maternal and infant early gut microbiota with respiratory infections in infants. Pediatr Res. 2025 Aug 20;1–14.