Determining the optimum cut-off IgM/ IgG ratio for predicting secondary dengue infections: An observational hospital based study from Central India.

Purpose: The present study was conducted to determine an optimum cut-off IgM/IgG ratio for differentiating between primary and secondary Dengue. The calculated cut-off was used to estimate the relative prevalence of primary and secondary Dengue in central India during the 2021 outbreak.

Methods: To differentiate between primary and secondary Dengue, optimum cut-off IgM/IgG ratio was determined using ROC curve analysis and Area under the curve (AUC) was calculated. For this 84 IgM positive samples were selected during the study period and Dengue IgM and IgG testing was performed.

Results: Based on sero-positivity for IgG antibodies, we observed a prevalence of 77.4% for secondary Dengue during this outbreak. IgM/IgG ratio of 1.59 delivered a sensitivity of 100% and specificity of 90.8%. Comparison of clinical characteristics revealed significant differences in rigors (p ​= ​0.04) and haemorrhagic manifestations (p ​= ​0.01) between the two types of infection.

Conclusions: This study revealed an overwhelming predominance of secondary Dengue during the reported outbreak, which hints at increasing endemicity in this region and raises the risk of severe clinical manifestations. An optimal IgM/IgG cut-off ratio, tailored according to the endemicity of this geographical region, is therefore suggested in this study.