The data could also reflect that the French Side has the capability/system to test more regularly for Chikungunya than does the Dutch Side.

I know several residents on the island over the past few years who have had more than one Dengue-like illness in a short period of time. While not impossible that both were Dengue subtypes, it is more likely that they also had Chikungunya before anyone was looking for it. It has probably been on St. Maarten longer than the documented cases show, and likely will be in the Caribean region for a while.