NS1 Rapid Card Test for Dengue Detection: Insights from the 2023 Outbreak in Bangladesh.

Background: Dengue poses a serious public health challenge in Bangladesh, with the 2023 outbreak resulting in over 1700 deaths, the highest on record. Despite apparent symptoms, many patients tested negative on the NS1 rapid antigen test, the primary diagnostic tool. This study assesses the reliability of the NS1 rapid test results by analyzing its sensitivity, specificity, and predictive values using RT-PCR as the gold standard. It also explores how viral serotypes and secondary infections may impact test performance, especially in NS1-negative cases. Methods: This cross-sectional study recruited febrile patients at two tertiary hospitals in Dhaka, Bangladesh, within 24 hours to 7 days of fever onset. Patients were selected based on physician-advised NS1 antigen testing, without restrictions on age, sex, or occupation. NS1 antigen test reports were collected from hospitals, and RNA testing via RT-PCR was conducted on all samples. Additional IgG and IgM tests were carried out for NS1-negative, RT-PCR-positive cases, and serotyping was performed on all RT-PCR-positive samples. Results: Of the 194 samples tested, 65 (33.5%) were RT-PCR positive for dengue. Among these, 25 (38.5%) were NS1-negative. Most RT-PCR-positive cases were male (67.7%), with the 16-45 age group most affected. Symptoms like body aches (83.1%) and headaches (70.8%) were common. The predominant serotype was DEN-2 (97.5% in NS1-positive and 84% in NS1-negative cases), known for lower NS1 sensitivity. NS1 test sensitivity, specificity, PPV, and NPV were 61%, 97%, 91%, and 83%, respectively. Early IgG positivity in NS1-negative cases suggested secondary infections. Conclusion: Despite the high specificity of NS1 rapid tests, moderate sensitivity demands alternative diagnostics like RT-PCR, which are crucial for better dengue management, especially in the presence of DEN-2 infections and associated secondary infections in Bangladesh.