Dengue virus serotype 4-leading serotype epidemic and its clinical and molecular characteristics in Vung Tau, South Vietnam, 2020-2021.

Dengue cases are reported annually in Vung Tau province, southern Vietnam; however, data on viral and host factors associated with disease severity are limited, particularly during epidemics driven by specific serotypes. We investigated the prevalence of dengue virus (DENV), its molecular epidemiology, and clinical-laboratory correlates of severity in patients with suspected dengue at Vung Tau General Hospital between September 2020 and May 2021. Among 1435 suspected cases, 639 (44.5%) were classified as DENV infection-negative, 60 (4.2%) presented with primary infection and 736 (51.3%) with secondary infection. DENV serotyping indicated that DENV-4 was the most prevalent serotype (50 patients, 37.6%), followed by DENV-2 (41, 30.8%), DENV-1 (39, 29.3%), and DENV-3 (3, 2.3%). Phylogenetic analysis revealed DENV-1 genotype I, DENV-2 genotype II (cosmopolitan) and genotype V (Asian I), and DENV-4 genotype I. Notably, DENV-4 exhibited two coexisting clades, suggesting that variations in clade distribution may have contributed to the epidemic. Although parameters commonly associated with dengue severity, such as white blood cell counts, platelet counts, and liver enzyme levels (AST and ALT), were comparable across serotypes, hemoglobin and hematocrit levels were elevated in DENV-4 infections compared with other serotypes. This elevation may indicate a higher risk of plasma leakage, a key feature of severe dengue, underscoring the potential clinical significance of DENV-4 during this epidemic. These findings highlight the epidemiological and clinical importance of DENV-4 and provide evidence for refining dengue control strategies in endemic areas.