Autochthonous dengue outbreak in Nîmes, South of France, July to September 2015

Abstract

In August and September 2015, seven locally acquired cases of dengue virus type 1 (DENV-1) were detected in Nîmes, south of France, where Aedes albopictus has been established since 2011. Epidemiological and entomological investigations allowed to steer vector control measures to contain transmission. An imported case from French Polynesia with onset fever on 4 July was identified as primary case. This outbreak occurred from 8 August to 11 September in a 300 m radius area. Six sprayings to control mosquitos were performed in the affected area. We describe the first considerable dengue outbreak in mainland France where only sporadic cases of autochthonous dengue were recorded previously (2010, 2013 and 2014). The 69 day-period between the primary case and the last autochthonous case suggests multiple episodes of mosquito infections. The absence of notification of autochthonous cases during the month following the primary case's symptoms onset could be explained by the occurrence of inapparent illness. Recurrence of cases every year since 2013, the size of the 2015 outbreak and continuing expansion of areas with presence of Ae. albopictus highlight the threat of arboviral diseases in parts of Europe. Thus, European guidelines should be assessed and adjusted to the current context.

Keywords: France; dengue virus; epidemiology; outbreaks; vector-borne infections; viral infections.