Improved and customized dengue serodiagnostics through combined NS1/IgM testing and novel dual-cut-off IgG ELISA

Background Accurate diagnostics of dengue virus (DENV) infection are essential for patient management, outbreak control, and vaccine implementation. Serological testing plays a key role, especially when molecular assays are unavailable or viremia subsides; yet, cross-reactivity with other flaviviruses remains a challenge. This study examined the diagnostic accuracy of four Euroimmun ELISAs, including a newly developed dual-cut-off IgG ELISA. Methods The Dengue Virus NS1 ELISA, Anti-Dengue Virus Type 1–4 ELISA (IgM), Anti-Dengue Virus Type 1–4 ELISA (IgG; native antigen/gE-based), and the novel Anti-Dengue Virus NS1 ELISA 2.0 (IgG; recombinant NS1-based, with an alternative higher cut-off for flavivirus-endemic regions) were analyzed. Sensitivity was determined using sera from 22 Vietnamese patients with RT-PCR-confirmed DENV infection, collected during acute (t1, 1–6 dpo), early convalescent (t2, 4–9 dpo), and late convalescent (t3, 13–19 dpo) phases. Specificity was assessed with samples from 500 healthy German blood donors (HBD) and 40 patients each with West Nile virus (WNV) or Zika virus (ZIKV) infection. Results Sensitivities were 90.5%/70.0%/0% (t1/t2/t3) for NS1, 33.3%/85.0%/77.3% for IgM, 66.7%/100%/100% for IgG, and 33.3%/65.0%/100% vs. 19.1%/50.0%/100% for IgG 2.0 (standard vs. alternative cut-off). Combined NS1/IgM testing achieved 100% sensitivity in single acute-phase samples. Combined IgM and IgG 2.0 testing confirmed recent infection by IgM/IgG seroconversion or ≥4-fold IgG increase in 85.7% of paired samples. Overall specificity was 85.7% (HBD/WNV/ZIKV: 95.0%/50.0%/5.0%) for IgG, compared to 95.7% (98.2%/95.0%/65.0%) and 99.5% (99.8%/97.5%/97.5%) for IgG 2.0 using standard and alternative cut-offs, respectively. Conclusions Euroimmun ELISAs support customized, highly accurate and versatile diagnostic strategies applicable to various dengue testing contexts. Combining NS1 and IgM ELISAs may offer a practical alternative to molecular assays during acute infection. The native antigen/gE-based IgG ELISA enables early sensitive IgG detection, although with limited specificity. With minimal cross-reactivity, the NS1-based dual-cut-off ELISA 2.0 (IgG) reliably captures DENV-specific IgG dynamics and enhances differentiation from other flaviviruses, which could provide an advantage in the use for convalescent-phase diagnostics, epidemiological surveillance, and pre-vaccination screening.