CXCL9 and Dengue hemorrhagic fever: Unlike the secondary infection arm of the cohort that identified high levels of some chemokines in cases progressing to DHF, no significant differences were found in plasma CCL17, CXCL5, CXCL8 and CXCL9, CCL2, CXCL10 and CXCL9 levels between clinical groups (Additional file 3: Fig. S6D–J).