Attenuated clinical presentation but severe laboratory evolution: a longitudinal analysis of dengue infection in older adults hospitalized in Northern Vietnam

OBJECTIVES: Older adults with dengue often present with atypical symptoms yet experience worse outcomes. We aimed to characterize age-related differences in clinical presentation, longitudinal laboratory dynamics, and in-hospital outcomes among hospitalized dengue patients in Northern Vietnam. METHODS: We conducted a prospective longitudinal observational study at a national tertiary infectious disease hospital in Hanoi. Adult patients with laboratory-confirmed dengue were stratified into two groups: older adults (≥60 years) and younger adults (<60 years). Clinical features, daily laboratory parameters, interventions, and outcomes were compared. Multivariable quadratic linear mixed-effects models, adjusted for comorbidities, were used to characterize nonlinear platelet recovery trajectories over the course of illness. RESULTS: A total of 444 patients were included (227 older adults, 217 younger adults). Older adults presented with lower admission temperatures and fewer classic symptoms but exhibited deeper nadir thrombocytopenia, higher peak aspartate aminotransferase (AST) levels, and a greater need for platelet transfusions. After adjustment for hypertension and diabetes, advanced age remained an independent predictor of more profound thrombocytopenia. In contrast, the association with higher peak AST was attenuated to a marginal trend after adjustment. Quadratic mixed-effects modeling demonstrated that age ≥60 years was associated with a distinct recovery curvature (P<0.001 for the age×day² interaction), independent of hypertension or diabetes. CONCLUSIONS: Older adults with dengue exhibit a distinct phenotype characterized by milder initial symptoms but severe laboratory abnormalities and a higher treatment burden. Longitudinal monitoring of laboratory trajectories, rather than relying solely on symptom-based assessment, is essential to optimize risk stratification and management in this vulnerable population.