BackgroundIn Vietnam, dengue has been endemic for many years, with most cases reported in children. Recently, epidemiological data show an increasing frequency in adults, especially for severe dengue. An unprecedented post-COVID-19 surge resulted in an exceptionally high number of hospitalized dengue cases. We aim to describe the clinical phenotypes and outcomes in Vietnamese adults with severe dengue during the 2022 outbreak and explore host-related factors associated with disease variability and severity, through a retrospective study.FindingsA total of 891 cases were included, with mean age 29 ± 10 years. 284/891 (31.9%) patients had a BMI ≥ 25 kg/m2, and 240/891 (26.9%) had comorbidities. The predominant severe clinical phenotype was dengue shock syndrome (DSS): 737/891 (82.7%) patients. 107/891 (12%) DSS cases were associated with other severe manifestations. Severe hemorrhage accounted for 90/891 (10.1%) patients. Among cases with organ involvement (211/891 - 23.7%), hepatic impairment was observed in 196/891 (22%) patients, renal impairment 25/891 (2.8%), cardiac impairment 14/891 (1.6%) and neurological impairment 13/891 (1.5%). 250/737 (33.9%) DSS patients developing ≥ 1 episode of recurrent shock. They were younger than those without recurrent shock (25.3 vs 28.4 years, p = 0.007). Factors associated with recurrent shock episodes were: having BMI ≥ 25 (OR: 1.65; 95% CI: 1.18; 2.3), day of illness ≤ 5 (OR: 2.16; 95% CI: 1.51; 3.09) and prior COVID-19 infection (OR: 2.57; 95% CI: 1.62-4.06). Indicators for the "associated severe phenotypes" (DSS associated with severe hemorrhage, with organ impairment, or both) were older age (p = 0.018) and presence of comorbidities (p < 0.001) compared to the DSS alone phenotype. Overall, 98.1% of patients had a good recovery.ConclusionsUnderstanding the variability and complexity of severe dengue clinical manifestations, along with the different host factors associated with these features, will contribute to formulating suitable treatment guidelines for this at-risk population.