This study plans to collect 106,667 fecal samples from Chinese infants and children under 6 years old, with multi-dimensional stratification based on geographic location, mode of delivery, antibiotic exposure, and developmental stage. Fecal gut microbiota will be profiled to construct a gut microbiome atlas, establish quantitative analytical models linking geographic regions, physiological phenotypes and microbial signatures, and identify key microbial biomarkers associated with core healthy phenotypes.

The human gastrointestinal tract harbors vast and diverse microbial communities collectively termed the "gut microbiota", widely known as the human body's "second genome". Research has demonstrated that during the colonization and maturation of gut microbiota in early infancy, these microbes participate in multiple core physiological processes including immune system maturation, nutrient absorption and metabolism, and nervous system development. Infancy represents a critical window for the establishment of intestinal microecology. Disturbances from adverse environmental factors such as antibiotic administration, inappropriate dietary patterns, and environmental pollution may trigger dysbiosis of microbial composition, which in turn elevates the long-term risk of developing obesity, allergic disorders, asthma, autism spectrum disorders and other diseases.

The formation and dynamic shifts of childhood gut microbiota are shaped not only by early-life exposures including mode of delivery, breastfeeding status and antibiotic use, but also by subsequent dietary patterns, living environments and socioeconomic status. For instance, high-fat diets reduce the abundance of beneficial gut bacteria, whereas Mediterranean-style diets support intestinal health; antibiotic treatment markedly diminishes microbial diversity and impairs community stability; urban-rural disparities also drive profound differences in gut microbial composition.

To date, domestic research on gut microbiota among infants and children has largely consisted of regional, small-cohort studies, lacking large-scale baseline datasets covering diverse geographic regions, age brackets and health statuses across China. This gap partially hinders the accumulation of scientific evidence for pediatric intestinal health research and disease prevention and control, and restricts the formulation of localized nutritional intervention strategies.

Accordingly, this study aims to conduct a large-cohort investigation covering infants and children aged 0 to 6 years nationwide. Through metagenomic sequencing and microbial isolation and culture of fecal specimens, we will construct gut microbiota atlases stratified by age, geographic region and health profile. The research will focus on associations between representative core gut taxa (e.g., Bifidobacterium) and indicators including children's nutritional status, immune development, allergic manifestations, gastrointestinal function and physical growth. We will also characterize microbial succession patterns during critical developmental windows in early life. Multivariate modeling and machine learning algorithms will be applied to screen microbial biomarkers strongly correlated with specific health conditions, and further dissect their underlying biological mechanisms.

This project is led by a professional research team with extensive experience in intestinal microecology. The team has previously completed gut microbiota profiling and analysis for thousands of infant subjects, obtained ethical approval and secured third-party laboratory qualification, laying a solid research foundation. Findings from this study will provide data support for early identification and intervention of common childhood illnesses, and deliver vital scientific evidence for developing personalized nutritional and health management strategies tailored to gut microecological signatures in Chinese children.

Inclusion Criteria:

1. Infants and children aged 0-6 years, regardless of gender.
2. Volunteers willing to participate in fecal sample collection and baseline health information gathering during the study period.
3. Legal guardians must agree to participate in the study and provide a signed written informed consent.

Exclusion Criteria:

1. Presence of congenital developmental anomalies, including but not limited to congenital cardiovascular malformations and chromosomal aneuploidy.
2. Immune system functional disorders, such as Severe Combined Immunodeficiency.
3. Diagnosis of hereditary diseases, such as genetic disorders caused by chromosomal abnormalities.
4. Any condition deemed unsuitable for participation by the investigator, including but not limited to failure to meet compliance assessment standards.

A total of 106,667 Chinese infants and children aged 0 to 6 years will be enrolled across all 34 provincial-level administrative regions of China