This prospective observational cohort study aims to investigate the relationship between immunosenescence and infectious diseases in older adults. Individuals aged 60 years and older, including elderly patients with infections and healthy controls, will be enrolled and followed longitudinally.

Clinical information, laboratory test results, and health assessment data will be collected. Biological specimens, including peripheral blood, urine, stool, sputum, and nasopharyngeal swabs, will be obtained during enrollment and follow-up. Participants will undergo regular assessments of health status, infection events, and aging-related clinical characteristics.

The study will evaluate age-related changes in immune function, immune cell composition, immune receptor repertoires, epigenetic characteristics, metabolic profiles, and respiratory and gut microbiota. By integrating clinical and multi-omics data, the study aims to identify biomarkers associated with immunosenescence, susceptibility to infection, disease severity, and clinical outcomes in older adults.

The results are expected to improve understanding of the mechanisms linking aging, immune dysfunction, and infectious diseases, and to support the development of predictive models and preventive strategies for infection management and healthy aging in elderly populations.

Inclusion Criteria for the Healthy Control Group

1. No clinical symptoms suggestive of infection, including fever, cough, dyspnea, fatigue, or myalgia.
2. No abnormal physical signs, including lymphadenopathy, hepatomegaly, splenomegaly, or skin rash.
3. Normal laboratory test results, including complete blood count (CBC), C-reactive protein (CRP), and liver and renal function tests.
4. Healthy adults without underlying chronic diseases, no history of infectious diseases within the previous 6 months, and generally normal cognitive function.
5. Male or female.
6. Able to understand the study procedures and voluntarily provide written informed consent.

Inclusion Criteria for the Infection Group 1.Age: 60 years or older; no gender restrictions. 2. Clinically diagnosed with an infectious disease by the treating physician. 3. The participant provides informed consent and signs the relevant documents.

-------------- Exclusion Criteria for the Healthy Control Group

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

Exclusion Criteria for the Infection Group

1. Final primary diagnosis is a non-infectious disease (e.g., connective tissue disease, tumor, or other conditions).
2. Positive culture results are determined by the clinician to be due to colonization or contamination rather than infection.
3. Refusal to participate in the study.
4. Patients in critical or severe conditions who are unable to cooperate with sample collection.
5. Other conditions deemed unsuitable for inclusion as determined by the researchers.

Adults aged 60 years and older