Mycobacterium tuberculosis pathogen load and associated inflammatory responses define infection severity in HIV-associated TB and interact with age to predict mortality.

BackgroundSepsis pathobiology is shaped by both pathogen load and host characteristics, yet pathogen load is rarely measurable in clinical cohorts. Severe HIV-associated tuberculosis (TB), a leading cause of critical illness in Africa, provides a unique model in which Mycobacterium tuberculosis bacilli load can be quantified. We investigated how pathogen load and age influence sepsis pathophysiology and mortality in this high-risk population.MethodsWe conducted a prospective cohort study of adults admitted with severe HIV-associated TB. Systemic bacillary load was estimated from multiple routinely collected TB diagnostics. Blood-based sepsis markers were summarised using principal components analysis, and pathophysiological processes were evaluated using directed acyclic graphs and regression modelling.FindingsAmong 519 patients with microbiologically confirmed TB, 75 (14.5%) died by day 28. Two major axes of host response were identified: PC1, capturing IL-6, CRP, and procalcitonin; and PC2, reflecting venous lactate, aspartate aminotransferase, and cytopenias. Both strongly correlated with bacilli load (PC1 r=0.46; PC2 r=0.43; both p