Imported cases of chikungunya, dengue, and Zika in mainland France

Enhanced surveillance for chikungunya, dengue, and Zika ended on November 30, 2023. The number of imported dengue cases identified in 2023 is the highest since this surveillance program began in 2006. More than two-thirds of imported dengue cases reported travel to the French departments in the Americas (Guadeloupe, French Guiana, Martinique) affected by dengue epidemics this year.

In total, 2,019 imported dengue cases were identified through this surveillance, including 1,760 in departments where the presence of Aedes albopictus has been documented. 30 cases of chikungunya (n=27 in departments colonized by Aedes albopictus) and 9 cases of Zika (n=9 in colonized departments) were also reported.

List of departments with documented presence of Aedes albopictus as of May 1, 2023

Ain, Aisne, Allier, Alpes de Haute-Provence, Alpes-Maritimes, Ardèche, Ariège, Aude, Aveyron, Bas-Rhin, Bouches-du-Rhône, Cantal, Charente, Charente-Maritime, Cher, Corrèze, Corse-du-Sud, Côte d’Or, Deux-Sèvres, Dordogne, Doubs, Drôme, Essonne, Gard, Gers, Gironde, Haute-Corse, Haute-Garonne, Hautes-Alpes, Haute-Loire, Hautes-Pyrénées, Haute-Savoie, Haut-Rhin, Hauts-de-Seine, Haute-Vienne, Hérault, Ille-et-Vilaine, Indre, Indre-et-Loire, Isère, Jura, Landes, Loir-et-Cher, Loire, Loire-Atlantique, Loiret, Lot, Lot-et-Garonne, Lozère, Maine-et-Loire, Mayenne, Meurthe-et-Moselle, Nièvre, Paris, Puy-de-Dôme, Pyrénées-Atlantiques, Pyrénées-Orientales, Rhône, Saône-et-Loire, Savoie, Seine-et-Marne, Seine-St-Denis, Tarn, Tarn-et-Garonne, Val-de-Marne, Var, Vaucluse, Vendée, Vienne, Yvelines, Val-d’Oise.

Locally acquired dengue cases in mainland France

Nine local dengue transmission outbreaks have been identified, resulting in a total of 45 dengue cases in mainland France. For each outbreak, entomological and epidemiological investigations were immediately launched, along with vector control measures.

In the Provence-Alpes-Côte d'Azur region:

• An outbreak involving 4 dengue cases was identified in Gardanne in the Bouches-du-Rhône department (13); the onset of symptoms for these cases occurred between the second half of July and mid-August.

• An outbreak involving 2 cases was identified in Nice in the Alpes-Maritimes (06); the onset dates of symptoms for these cases range from early August to mid-September.

• An outbreak of 10 cases has been identified in Boulbon in the Bouches-du-Rhône (13); the onset dates for these cases range from late July to late September.

• One case was identified in Antibes in the Alpes-Maritimes (06), with symptoms beginning in late September.

In Occitanie:

• An outbreak of 11 cases has been identified within a limited area of Perpignan in the Pyrénées-Orientales (66); the onset dates for these cases range from late July to mid-August.

• A cluster of 9 cases was identified in Gagnières in the Gard (30). The onset dates for these cases range from late August to late September.

• A cluster of 3 cases was identified in Montpellier in the Hérault (34), with symptom onset dates ranging from mid-September to late September (Note: The third case was initially identified as an imported case but was subsequently reclassified as a locally transmitted case based on epidemiological data and additional analyses conducted by the National Reference Center for Arboviruses).

In Auvergne-Rhône-Alpes:

• An outbreak involving 2 cases was identified in Bourg-lès-Valence in the Drôme department (26); the onset dates of symptoms ranged from late August to mid-September.

In Île-de-France:

• An outbreak involving 3 cases was identified in Limeil-Brévannes (94). Symptoms in these cases began in September.

Thanks to the epidemiological investigations conducted, the imported case responsible for the transmission was identified in 3 of the 9 clusters investigated. For two clusters, the primary imported case had traveled to Martinique, and for one cluster, the primary imported case had traveled to Guadeloupe.

For 7 of the 9 local outbreaks, the dengue virus serotype was identified. It was serotype 2 (DENV-2) for 4 outbreaks, serotype 1 (DENV-1) for 2 outbreaks, and serotype 3 (DENV-3) for 1 outbreak.

The maximum distance between the residences of cases within the same transmission cluster did not exceed 950 meters.

Enhanced surveillance aims to rapidly identify cases of dengue, chikungunya, and Zika in mainland France during the active season of the vector, the Aedes albopictus mosquito. Early case identification helps limit the risk of local transmission of these diseases through rapid intervention by vector control services (LAV).

Detailed data on arbovirus surveillance in mainland France in 2023 will be presented in an article in the BEH.