Importance of case definition to monitor ongoing outbreak of chikungunya virus on a background of actively circulating dengue virus, St Martin, December 2013 to January 2014

Since 5 December 2013, chikungunya virus (CHIKV) has been demonstrated to circulate in the Caribbean, particularly on Saint Martin. This region is facing a concomitant dengue virus (DENV) outbreak. Of 1,502 suspected chikungunya cases, 38% were confirmed chikungunya and 4% confirmed dengue cases, with three circulating serotypes. We report in addition 2.8% CHIKV and DENV co-infections. This study highlights the importance of the case definition for clinicians to efficiently discriminate between DENV infection and CHIKV infection.