Figure 2. DENV IgM ELISA endpoint titers, by serotype, of paired patient serum samples acquired at 2–4 time points after symptom onset, 2013–2018. A–C) Serum samples from returning travelers with residence in Germany: DENV-1 positive (A, B); DENV-2 positive (C). D–F) Serum samples from residents of DENV-endemic country Sri Lanka: DENV-2 positive (D, E); DENV-4 positive (F). Data lines indicate average titers; error bars indicate SDs. The antigens in the ELISA were Equad proteins (i.e., envelope protein from each DENV serotype with 4 amino acid changes T76R, Q77E, W101R, and L107R). DENV, dengue virus.