To establish eligibility for inclusion in a phase 1b , randomised , double-blind , placebo-controlled , proof-of-concept trial , individuals aged 21-65 years who had had a fever ( 38C ) for less than 48 h , met at least two criteria indicating probable dengue infection , and had a positive result on a dengue point-of-care test kit or PCR assay were referred for screening at a centre in Singapore between July 30 , 2012 , and March 4 , 2013 .