Sample collection
Four hundred and thirty-nine hospitalized suspected adult dengue patients, 13 years of age or older were recruited from three different hospitals, namely Hospital Universiti Sains Malaysia (HUSM), Hospital Raja Perempuan Zainab II (HKB), and Hospital Sungai Buloh (HSB). Among these, 185 confirmed dengue patients were from HUSM and HKB and were recruited between 2008 and 2010. Both hospitals are located in the state of Kelantan. Another 96 patients were confirmed dengue patients from HSB (recruited between 2010 and 2012), located in the state of Selangor. Blood samples were collected on the first day of admission, and the clinical data were retrieved from standardized case report forms after the patients were discharged. Laboratory confirmation, namely an