Preliminary report of an autochthonous chikungunya outbreak in France, July to September 2017.

In August 2017, an autochthonous chikungunya case was reported in south-east France. By mid-September, eight additional autochthonous cases were found in the index case's neighbourhood, where the chikungunya virus vector was observed. Genomic characterisation identified an East-Central South African (ECSA) lineage strain, probably from the Central African region and carrying an adaptive mutation facilitating transmission by . The event confirms we need early case detection and response to contain chikungunya in Europe.