Subjects were enrolled from the Early DENgue (EDEN) study, a dengue investigation conducted at a primary healthcare clinic in Singapore, for which local ethical approval had been granted, and informed consent from patients obtained. Participation required a PCR diagnosis of fever with duration less than 3 days (for the details of the PCR diagnosis, see [22] ). The enrolled dengue cases were either of serotype 1 or 3. Ten dengue positive subjects (n = 10, 3 males) were selected to represent the most severe cases of dengue by the criteria of a platelet counts below 30 (x 10 3 /ml; range 8-30, mean 20.5). Their mean age was 43.2 years (range 24-67). The mean fever was 38.3uC (range 37.7-39.1) at the first visit (Time Point 1), with a mean duration of 43 hours (range 14-72) from the onset of the fever. The second visit (Time Point 2) occurred at 80 to 96 hours after the first visit, mean fever was 37.1uC (range 36.2-38.7). Dengue negative patients were enrolled with the same criteria (fever with no respiratory infection symptoms), but were PCR negative for dengue. Ten subjects were taken with (n = 10, 4 males) a mean age of 43.2 years old (range 24-67). Their mean fever was 38.4uC (range 37.6-39.4) with a mean duration 27 hrs (range 8-60) at the first visit (Time Point 1). The convalescence sample was collected at the third visit which was 3 to 4 weeks later (Time Point 3). At each time point, a 2.5 ml blood sample was collected in PAXgene tubes for RNA analysis. A 10 ml blood sample was collected, serum was separated within 5 hrs and stored at 280uC. Serum IP-10 and I-TAC concentrations were measured using ELISA kits from R&D Systems as per manufacturers instructions.