Dengue IgM ELISA Dataset from Trinidad and Tobago: Analytical Evaluation of Borderline Serological Results and Seroprevalence Estimation

Background: Dengue remains a major public health concern in tropical and subtropical regions, where serological assays are widely used for diagnosis and epidemiological surveillance. However, borderline enzyme-linked immunosorbent assay (ELISA) IgM results represent a frequent source of diagnostic uncertainty and may substantially influence estimates of disease prevalence. This study evaluated the impact of different analytical approaches to borderline ELISA results on dengue IgM seroprevalence among patients with suspected dengue infection in Trinidad and Tobago. Methods: A retrospective laboratory-based study was conducted using 161 consecutive serum samples submitted for routine dengue serology. Dengue virus-specific IgM antibodies were detected using the EUROIMMUN Anti-Dengue Virus ELISA (IgM). Samples were analysed in four independent laboratory batches (31, 29, 53, and 48 specimens). Sero-prevalence was calculated using three predefined analytical strategies: (i) conservative (borderline results classified as negative), (ii) exclusion (borderline results omitted from analysis), and (iii) liberal (borderline results classified as positive). Exact 95% confidence intervals (CIs) were calculated using the Clopper–Pearson method. Batch-to-batch reproducibility was evaluated using Cochran's Q heterogeneity test. Results: Of the 161 serum samples analysed, 20 (12.4%) were positive, 29 (18.0%) were borderline, and 112 (69.6%) were negative. Under the conservative analytical approach, the estimated dengue IgM seroprevalence was 12.4% (20/161; 95% CI: 7.7%–18.6%). Excluding borderline samples increased the estimated seroprevalence to 15.2% (20/132; 95% CI: 9.6%–22.6%), whereas classifying all borderline samples as positive yielded a prevalence of 30.4% (49/161; 95% CI: 23.4%–38.3%). Batch-specific seroprevalence estimates ranged from 10.3% to 15.1%, with no significant heterogeneity among analytical batches (Q = 0.41, p = 0.94; I² = 0%), demonstrating excellent reproducibility across laboratory runs. Conclusions: The estimated seroprevalence of dengue IgM was highly dependent on the analytical treatment of borderline ELISA results. Conservative classification provided the most cautious and reproducible estimate of recent dengue infection, while liberal interpretation substantially increased the apparent disease burden. These findings emphasize the importance of transparent reporting and standardized interpretation of equivocal serological results to improve the accuracy and comparability of dengue surveillance data, and support evidence-based public health decision-making.