Reducing the risk of local dengue transmission in France

France operates a national enhanced-surveillance system for dengue, chikungunya and Zika, running each May-November in administrative districts (départements) where the invasive mosquito Aedes albopictus is established. Aedes albopictus, whose European range is expanding with climate change, was present in 67 of 96 mainland French départements by 2022, and France records the highest number of autochthonous (locally transmitted) dengue cases among EU countries.

The system aims to detect imported and autochthonous cases as early as possible and trigger public health responses to limit onward transmission, through raising awareness among health professionals and the public, systematic testing and notification, entomological investigation, and vector control.

Dengue has been a mandatory notifiable disease in France since 2006. Clinicians and laboratories report cases to Regional Health Agencies, which relay data to Santé publique France; laboratory diagnostic databases are reviewed daily to catch unreported cases. Each autochthonous case triggers an epidemiological investigation, door-to-door surveys covering up to 1,000 households within a 150-250m radius, and entomological control (breeding-site destruction and targeted larvicide/adulticide treatment within 150-200m of case locations).

Between 2010 and 2021, France recorded 48 locally transmitted dengue cases across 19 separate transmission events; during the 2022 season alone, 65 locally transmitted cases were recorded, a record high, including the largest documented dengue transmission event in Europe (34 cases across Saint-Jeannet and Gattières). A national assessment of invasive-species costs (InvaCost database) attributed 36% of all invasive-species costs in France, at least EUR 410 million between 1993 and 2018, to Aedes mosquitoes, of which 79% was health-related damage and 13% vector-control spending. No quantitative estimate exists of cases or deaths averted by the surveillance system itself.

Cited evaluations describe the system as sensitive enough to detect autochthonous transmission and efficient enough to limit its spread, though a long reporting delay for imported cases has been identified as a main driver of onward transmission. Door-to-door surveys are reported to be well received by residents, and targeting awareness campaigns at the individual-community level is described as more effective than campaigns run at the broader NUTS3 regional level.