Association between immunosenescence and high bacterial load in elderly patients with pulmonary tuberculosis: A retrospective cohort study conducted in Southwest China, 2013-2020

PURPOSE: This study aimed to characterize the clinical and pathogen features of TB in the elderly through comparison with non-elderly patients, and to identify risk factors for high transmissibility in this population. METHODS: We enrolled 1,332 consecutive inpatients aged ≥65 years with active pulmonary tuberculosis between 2013 and 2020, along with a matched group of non-older tuberculosis patients. Multivariable logistic regression identified independent predictors of sputum smear positivity in the elderly cohort. RESULTS: Older TB patients are mostly male (70.3%) and often have diabetes (25.8%). They show significant immune decline (lower lymphocytes, T-cells, IFN-γ; 29.6% IGRA false-negative rate), poor nutrition (lower BMI, albumin, hemoglobin), and increased inflammation (higher CRP, ESR, IL-6). They are more likely to test positive on sputum smear (29.7% vs. 19.0%, P < 0.001) and molecular tests, but have much lower rifampicin resistance (5.4% vs. 18.0%, P < 0.001). Retreatment (aOR 2.29), cavitary disease (aOR 5.31), and diabetes (aOR 2.03) were the main factors linked to sputum smear positivity. CONCLUSIONS: Older TB patients exhibit immune senescence associated with high IGRA false-negative rates, poorer nutrition, more inflammation, higher bacillary loads, and less drug resistance than younger patients. These associations warrant further investigation. Rapid identification of prior treatment, cavitary disease, or diabetes remains crucial for transmission control.