Figure 4

Abnormal antibody response observed in sequential samples in dengue patients. Sera were collected at the indicated days and the titers of antibodies were measured as previously described [71]. (A) Primary dengue virus infection. These samples were determined to be from secondary patients by the IgM/IgG ratio recorded at the early acute stage. There is no robust amplification in IgG, indicating that these patients should be recategorized as primary infections. (B) Secondary dengue virus infection. These samples were determined to be from primary dengue patients by the IgM/IgG ratio recorded at the early acute stage. These samples demonstrate IgG amplification, indicating that these patients should be considered secondary patients. IgM/IgG ratios, obtained at the acute stage, cannot accurately distinguish between primary and secondary virus exposure in dengue patients.