Differentiating Secondary Dengue Using IgG/IgM Antibody Ratio: A Cross-sectional Study

Introduction: Dengue is a viral infection with diverse clinical manifestations. Infection in most of the patients is subclinical. It may also present as undifferentiated fever, severe dengue like Dengue Haemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS). Secondary dengue infection predisposes to severe dengue, a serious threat to the community as they increase morbidities and mortality. The diagnosis of secondary infection is either by Polymerase Chain Reaction (PCR) to detect the serotype or dengue IgG/IgM antibody ratio. A ratio of more than 1.1 is evidence of secondary dengue. Aim: To find out the prevalence of secondary dengue by measuring the dengue anti-IgG/IgM ratio by Enzyme Linked Immunosorbent Assay (ELISA) test. Materials and Methods: This cross-sectional observational study was conducted at Government Kilpauk Medical College, Chennai for a period of six months from July 2021 to December 2021. Sample size was 450 calculated at 95% confidence level, (CI 28.3-38.3) with 33.3% as prevalence. Blood samples were collected and Nonstructural Protein 1 (NS1) antigen assay was done. The IgG and IgM antibodies assays were done for NS1 antigen positive individuals. The IgG/IgM ratio was calculated in patients who were positive for both IgG and IgM. Statistical analysis was done with Statistical Package for Social Sciences (SPSS) version 20.0. Percentage, mean and standard deviation were calculated. Results: Total of 450 patients were included, out of which 194 were NS1 antigen positive, 106 were males and 88 females with the mean age 25±14.85 years. NS1 antigen was positive in 89.17%. Two-tailed Fisher’s-exact test showed a significant proportion of patients among NS1 positive were positive for both IgG and IgM. An IgG/IgM ratio of >1.1 was found in 62.04%. The association between IgG/IgM ratio of >1.1 and thrombocytopenia was significant [p-value=0.00504, Odd’s ratio (OD) =3.316]. Conclusion: Dengue IgG/IgM antibody ratio of more than 1.1 on the third day of symptom onset and the platelet count assist in the early diagnosis of secondary dengue thereby helps clinicians to initiate the appropriate treatment at the right time, reduce mortality rate and decrease the economic burden of the country.