Clinical and Virological insights into acute primary Dengue infection from a Northeast Indian frontier state: A cross sectional study

PURPOSE: Dengue virus (DENV) is a major public health concern in India, with rising reports of dual-serotype infections associated with severe clinical outcomes. Tripura has witnessed a significant spike in Dengue cases, suggesting the co-circulation of multiple serotypes. This study aimed to assess the acute primary Dengue infections in Tripura and evaluate the association of clinical features, viral load, and NS1 sample O.D. ratio with such infections. METHODS: A prospective cross-sectional study was conducted from April 2023 to March 2025 across all eight districts of Tripura. NS1-positive, IgG-negative patients with acute febrile illness (≤5 days) were included. A subset of samples underwent viral load estimation and serotyping via qRT-PCR and multiplex PCR. Data were analyzed using SPSS v21. Student's t-test and ROC curve analysis were applied to assess associations. A p-value <0.05 was considered statistically significant. RESULTS: Among 506 primary Dengue cases, 102 underwent qRT-PCR; Among 91 positive samples, DENV2 was the predominant circulating serotype (80.2%). 19.8% showed concurrent dual-serotype infections, predominantly DENV-1/2. These infections had significantly higher viral loads (6.36 ± 0.96 log copies/ml) and NS1 O.D. ratios (21.6 ± 6.2) compared to mono-serotype cases. ROC analysis confirmed both log viral load and NS1 O.D. ratio as having strong association with dual serotype Dengue co-infection. CONCLUSION: Dual-serotype Dengue infections are emerging in Tripura. Elevated viral load and NS1 O.D. ratio have significant association with concurrent infection by dual serotypes in the region. Larger, long-term regional studies are needed for broader validity.