As population aging accelerates, infectious diseases have become a major factor affecting the health, quality of life, and survival outcomes of older adults. Immunosenescence, chronic low-grade inflammation (inflammaging), and dysbiosis of the respiratory and gut microbiota are considered important mechanisms underlying increased susceptibility to infection and a higher risk of severe disease in older adults. However, the interactions among these factors and their impact on infection-related outcomes remain incompletely understood.

Building upon a previously established pilot cohort of older adults, this study aims to further identify and validate key biological characteristics and risk factors associated with infectious diseases through large-scale population follow-up. A large prospective cohort of older adults will be established, while retrospective healthcare data collected since 2019 will also be integrated. Demographic information, comorbidities, medication history, infection-related clinical data, and biological specimens, including blood, urine, fecal, and respiratory samples, will be collected for long-term longitudinal follow-up. By integrating immunological assessments, immune repertoire analyses, microbiome profiling, and other multi-omics technologies, this study will systematically evaluate the effects of immunosenescence, respiratory and gut microbiome alterations, and environmental and climatic factors on the occurrence, severity, and prognosis of infectious diseases in older adults. The study aims to identify key biomarkers and microbial signatures associated with infection risk and to develop risk prediction and early warning models for infectious diseases in older adults, thereby providing scientific evidence for precision prevention, optimized clinical management, and public health decision-making in aging populations.

Inclusion Criteria:

- General Cohort Inclusion Criteria

1. Adults aged 60 years or older who are in generally good health, defined as having no severe organ dysfunction that significantly affects daily living activities (e.g., decompensated heart, liver, or kidney failure), adequate nutritional status (without significant wasting or malnutrition), and the ability to communicate and comply with study procedures.
2. Male or female.
3. Able to understand the study and voluntarily provide written informed consent.

Infection Cohort Inclusion Criteria

1. Adults aged 60 years or older, regardless of sex.
2. Patients with an infectious disease diagnosed by a qualified clinician.

Exclusion Criteria:

• General Cohort Exclusion Criteria

  1. Refusal to participate in this study.
  2. Any other condition that, in the opinion of the investigator, makes the participant unsuitable for enrollment.

Infection Cohort Exclusion Criteria

1. Final primary diagnosis is a non-infectious disease (e.g., connective tissue disease, malignancy, or other non-infectious conditions).
2. Positive culture results determined by the treating clinician to represent colonization or contamination rather than true infection.
3. Refusal to participate in this study.
4. Critically ill patients or those unable to cooperate with specimen collection procedures.
5. Any other condition that, in the opinion of the investigator, makes the participant unsuitable for enrollment.

Adults aged 60 years and older